IRC 6166 Estate Tax Installment: Closely Held Business

1. Overview: The Estate Liquidity Problem and IRC 6166

Quick Reference: IRC 6166 at a Glance

The core problem: Federal estate tax is due in full within 9 months of the decedent's date of death (verify at IRS.gov and in current IRC text). Closely held business interests and farm assets are illiquid: they cannot be quickly converted to cash without destroying the enterprise or triggering a forced sale at distressed prices. This mismatch between the estate tax due date and asset liquidity has been the central estate planning challenge for family business owners for decades.
What IRC 6166 provides: IRC 6166 allows the executor of a qualifying estate to elect to defer payment of the portion of federal estate tax attributable to a qualifying closely held business interest, paying interest only for the first 5 years and then paying principal and interest in up to 10 equal annual installments over the following years -- a maximum total deferral of up to 14 years from the original estate tax due date. The deferred amount carries a preferential reduced 2% interest rate on the first tier of deferred tax, making the cost of deferral significantly lower than commercial borrowing in many environments. All period and rate statements in this guide are hedged to current IRC text and IRS.gov; verify before advising any client.
Post-OBBBA context: The One Big Beautiful Bill Act (OBBBA, Pub. L. 119-21, July 4, 2025) permanently set the basic exclusion amount (BEA) at $15 million per person, indexed for inflation. This significantly raises the estate tax threshold for most clients and removes many estates from the estate tax system entirely. However, for closely held business owners with gross estates above the applicable exclusion amount, the liquidity problem remains acute: a $50 million family business that is 80% closely held still faces estate tax on the taxable portion, and cash to pay that tax must come from somewhere. IRC 6166 remains the primary statutory solution for those clients. Verify the current indexed BEA at IRS.gov and in the IRC 2010 guide (see Related Guides).
What IRC 6166 does not provide: IRC 6166 covers only federal estate tax. It does not extend the time to pay state estate or inheritance taxes (which remain governed by applicable state law); it does not eliminate the underlying estate tax liability; and it does not protect against acceleration of the full deferred balance if certain events occur (see Section 9). It is also distinct from IRC 6161, which provides a discretionary 12-month hardship extension that requires IRS approval and is not limited to closely held business interests but does not provide the same long-term deferral benefit.
OBBBA did not amend IRC 6166: The OBBBA made no direct amendments to IRC 6166. All mechanics described in this guide -- the 35% test, the qualification rules, the payment schedule, the interest rate tiers, the acceleration events, and the security requirements -- remain under pre-OBBBA law as in effect and as potentially modified by subsequent regulatory guidance. Verify the current status of all IRC 6166 provisions at IRS.gov.

2. Eligibility: The 35% Test

Warning: The 35% Test Is Against ADJUSTED Gross Estate -- Not Gross Estate

The IRC 6166 eligibility threshold requires that the value of the closely held business interest exceed more than 35 percent of the ADJUSTED gross estate -- that is, the gross estate reduced by deductions allowable under IRC 2053 (claims against the estate, mortgages, debts, and administration expenses) and IRC 2054 (losses during estate administration). Practitioners who incorrectly test the closely held interest as a percentage of the unadjusted gross estate will overstate the qualifying percentage and may incorrectly advise a client that the estate qualifies when it does not.

The deductions available under IRC 2053 and IRC 2054 can be substantial and can significantly reduce the adjusted gross estate, thereby increasing the percentage that the closely held business interest must represent in order to clear the 35% threshold. This computation must be performed precisely, with confirmed values for all deductible claims and expenses, before advising the client to rely on IRC 6166 eligibility. Verify all components of the adjusted gross estate computation at IRS.gov and under current IRC 2053 and IRC 2054 guidance.

2.1 The Statutory Threshold

Under IRC 6166(a)(1) (hedge: verify at IRS.gov and in current IRC text), an executor may elect to pay estate tax in installments if the value of the decedent's interest in a closely held business (as defined in IRC 6166(b)(1)) exceeds more than 35 percent of the adjusted gross estate. Note the statutory phrasing: the interest must represent MORE THAN 35 percent of the adjusted gross estate -- a decedent whose closely held business interest represents exactly 35 percent of the adjusted gross estate does not qualify. Verify the statutory threshold at IRS.gov.

2.2 Definition of Adjusted Gross Estate

For purposes of the IRC 6166(a)(1) threshold (hedge: verify at IRS.gov and in current IRC text), the adjusted gross estate is the gross estate (the total value of all property includible in the gross estate under IRC 2031 through IRC 2046) reduced by the deductions allowable under IRC 2053 (expenses, indebtedness, and taxes) and IRC 2054 (losses). The resulting figure is the denominator in the 35% fraction; the closely held business interest value (numerator) must exceed 35% of this denominator. Because IRC 2053 deductions -- which include mortgages, debts, administration expenses, and claims against the estate -- reduce the denominator, they can make it easier (by increasing the ratio) or harder (by reducing the absolute denominator threshold) to meet the test depending on the facts. Verify the current definition and computation of adjusted gross estate under IRC 6166(a)(1) at IRS.gov.

2.3 Timing of the Valuation

The value of the closely held business interest is determined as of the decedent's date of death (or the alternate valuation date under IRC 2032, if elected). Valuations of closely held interests typically require a qualified appraisal by a business valuation specialist. Because the 35% threshold is a hard eligibility gate, the valuation must be complete and defensible before the executor makes the IRC 6166 election (or a protective election; see Section 5). Verify the applicable valuation standards and IRS appraisal requirements at IRS.gov.

2.4 Only Qualifying Interests Count Toward the 35%

Not every business interest in the gross estate qualifies as a "closely held business interest" for IRC 6166 purposes. Only interests that satisfy the definition in IRC 6166(b)(1) are eligible (see Section 3). An estate may include multiple business interests -- some qualifying and some not -- and only the qualifying interests may be counted toward the 35% threshold. Furthermore, when multiple interests in different businesses are involved, the aggregation rules of IRC 6166(c) (see Section 4) must be satisfied before those interests can be combined to meet the threshold. Verify the current rules at IRS.gov.

3. Definition of "Interest in a Closely Held Business"

Warning: Passive Assets Inside an Entity Reduce the Qualifying Interest Value

Under IRC 6166(b)(8) and IRC 6166(b)(10) (hedge: verify at IRS.gov and in current IRC text), if a closely held business entity holds passive assets (assets that are not active trade or business assets), the value of the decedent's interest that is treated as a qualifying closely held business interest is reduced proportionately to exclude the passive asset portion. If passive assets represent a significant portion of the entity's total value, the effective qualifying interest may be reduced below the 35% adjusted gross estate threshold even if the total entity interest exceeds that threshold on its face.

This is one of the most frequently overlooked issues in IRC 6166 eligibility analysis. Practitioners advising clients on the election must audit the entity's assets for passive holdings (including excess cash, investment securities not used in the trade or business, and non-operating real estate) and apply the IRC 6166(b)(8)/(b)(10) reduction before concluding that the 35% threshold is met. Verify the current passive asset rules and their interaction with the 35% test at IRS.gov and under current IRC 6166(b)(8) and (b)(10) guidance.

3.1 Sole Proprietorship

Under IRC 6166(b)(1)(A) (hedge: verify at IRS.gov and in current IRC text), any interest in a trade or business carried on as a sole proprietorship qualifies as a closely held business interest. The entire net value of the sole proprietorship's trade or business assets, properly reduced for business liabilities, is the qualifying interest. Assets of the sole proprietorship that are not used in the active trade or business are subject to the passive asset rules (see above). Verify the applicable standards for sole proprietorship qualification and asset characterization at IRS.gov.

3.2 Partnership Interests

Under IRC 6166(b)(1)(B) (hedge: verify at IRS.gov and in current IRC text), a partnership interest qualifies as a closely held business interest if either: (a) 45 or fewer partners held interests in the partnership; or (b) the decedent held 20 percent or more of the total capital interest in the partnership. Both the 45-partner threshold and the 20% capital interest threshold are hedged to current IRC 6166(b)(1)(B) and IRS.gov; verify the current thresholds and how "total capital interest" is computed at IRS.gov before advising a client. Family attribution rules under IRC 267(c) may aggregate the interests of certain family members with the decedent's interest for purposes of the 20% test; verify the applicable attribution rules at IRS.gov.

3.3 Corporation Interests

Under IRC 6166(b)(1)(C) (hedge: verify at IRS.gov and in current IRC text), stock in a corporation qualifies if either: (a) 45 or fewer shareholders held stock in the corporation; or (b) the decedent held 20 percent or more of the total value of the voting stock of the corporation. Both thresholds are hedged to current IRC 6166(b)(1)(C) and IRS.gov; verify the current thresholds and how voting stock is measured at IRS.gov. The attribution rules of IRC 267(c) may also apply to aggregate family members' stock with the decedent's for the 20% test; verify at IRS.gov.

3.4 Family Attribution Rules

Under IRC 6166(b)(2) (hedge: verify at IRS.gov and in current IRC text), for purposes of determining the number of partners or shareholders and the decedent's percentage interest, certain family attribution rules apply. The interests of the decedent's spouse, children, grandchildren, and parents may be treated as the decedent's under applicable attribution rules, potentially allowing the decedent to satisfy the 20% capital or voting interest threshold even if the decedent's direct ownership was below 20%. Verify the current family attribution rules and which relationships are covered at IRS.gov and under applicable IRC provisions.

3.5 Holding Companies and Passive Assets

IRC 6166(b)(8) (hedge: verify at IRS.gov and in current IRC text) addresses holding companies and the passive asset reduction. When a closely held business entity itself holds interests in other entities, or holds assets that are not used in an active trade or business, those "passive assets" must be excluded from the qualifying closely held business interest value. The reduction is made proportionately based on the ratio of passive assets to total assets. IRC 6166(b)(10) contains related rules for certain tiered-entity situations; verify the full scope of the passive asset rules at IRS.gov and under current IRC 6166(b)(8) and (b)(10) before completing the 35% test computation.

4. Aggregation of Multiple Business Interests (IRC 6166(c))

4.1 Same Trade or Business

Under IRC 6166(c) (hedge: verify at IRS.gov and in current IRC text), if the decedent held interests in the same trade or business conducted through more than one entity (for example, a sole proprietorship and a related partnership that together operate a single business), those interests may be aggregated and treated as a single closely held business interest for purposes of the 35% test. Verify what constitutes the "same trade or business" under IRC 6166(c) and applicable Treasury regulations and IRS guidance at IRS.gov.

4.2 Two or More Different Businesses

If the decedent held interests in two or more separate and distinct closely held businesses, those interests may be aggregated for IRC 6166 purposes ONLY if the decedent held 20 percent or more of the qualifying interest in each separate business (hedge: verify the current 20% threshold and aggregation conditions under IRC 6166(c) and IRS.gov). This is a higher bar than simply holding qualifying interests in multiple businesses. An estate that holds minority interests in several businesses -- each below 20% -- would generally not be able to aggregate those interests to meet the 35% threshold unless family attribution raises each individual interest above 20%. Verify the aggregation rules in full at IRS.gov.

4.3 Strategic Implications for Pre-Death Planning

Understanding the IRC 6166(c) aggregation rules is important for pre-death planning as well. A business owner who holds fragmented minority interests in multiple entities that together represent a substantial portion of the estate may not be able to aggregate them to meet the 35% test unless the ownership structure is consolidated or reorganized before death. Conversely, reorganizing interests to consolidate them into fewer entities (while respecting IRC 2036/2038 issues and other estate tax rules) may improve IRC 6166 eligibility. Verify any restructuring strategy against all applicable IRC provisions and IRS guidance at IRS.gov before advising a client.

5. Making the Election: Form 706 and Rev. Proc. 2011-42

5.1 Who Makes the Election

The IRC 6166 election is made by the executor of the estate -- the person responsible for filing Form 706, the United States Estate (and Generation-Skipping Transfer) Tax Return. If there is no executor appointed (for example, when an estate passes without formal probate for certain assets), the election must be made by the person in possession of the property; verify the applicable rules at IRS.gov. Only one election may be made for each estate; there is no provision for splitting the election among co-executors. Verify the current election authorization rules at IRS.gov.

5.2 Deadline: Form 706 Due Date

The IRC 6166 election must be made on or before the due date (including extensions) of Form 706 (hedge: verify at IRS.gov and in current IRC text). The standard Form 706 due date is 9 months after the decedent's date of death. A 6-month extension of time to file is available on Form 4768 (Application for Extension of Time to File a Return and/or Pay U.S. Estate (and Generation-Skipping Transfer) Taxes); if a Form 4768 extension is obtained, the election deadline is correspondingly extended to the extended due date. Verify the current Form 706 due date rules and extension procedures at IRS.gov.

5.3 How the Election Is Made

The election is made by attaching an election statement to Form 706 and completing Schedule A-1 (Section 2032A Valuation) or the applicable estate tax form schedule. Rev. Proc. 2011-42 (hedge: verify that this revenue procedure remains current and has not been superseded; check IRS.gov for any updates or supplemental guidance) provides the procedural requirements for the election statement. The statement must include: (a) the amount of estate tax to be paid in installments; (b) the number of installments; (c) the date the first installment is to be paid; and (d) the identity of the closely held business interest and its value. Verify all election statement requirements at IRS.gov and in Rev. Proc. 2011-42 (as currently in effect) before filing.

5.4 Protective Elections

When the estate's eligibility for IRC 6166 is uncertain pending final valuation of the closely held business interest, a protective election may be filed. A protective election preserves the right to make the IRC 6166 election if the business interest ultimately qualifies, without requiring the executor to commit to installment payments when eligibility is not yet confirmed. The protective election must still be filed by the Form 706 due date (including extensions). Verify the current IRS procedures for filing a protective IRC 6166 election at IRS.gov.

5.5 Late Elections

Late elections -- that is, elections filed after the Form 706 due date (including any extensions) -- are generally not available under IRC 6166 (hedge: verify at IRS.gov for any relief procedures, private letter ruling authority, or other IRS guidance that may provide relief in limited circumstances). Practitioners must calendar the Form 706 due date and any available extension dates carefully and not assume that an IRC 6166 election can be cured or made retroactively if the original deadline is missed. Verify at IRS.gov.

6. Payment Schedule: 5-Year Deferral Plus 10 Annual Installments

IRC 6166 Payment Structure at a Glance (Illustrative Only -- Verify at IRS.gov)

First 5 years (interest only): No principal is due on the deferred estate tax during the first 5 years following the original estate tax due date. Only the accrued interest on the deferred balance is payable during this period. The first interest-only payment is generally due on the regular due date of Form 706.

Years 6 through 15 (installments of principal plus interest): Beginning with the first annual installment due in the sixth year, the estate pays one of up to 10 equal annual principal installments plus accrued interest. Each installment represents approximately one-tenth of the total deferred estate tax principal, plus interest accrued on the remaining balance.

Maximum duration: Up to 14 years total from the original estate tax due date (hedge to current IRC 6166(a)(3) and IRS.gov; verify the current maximum period before advising any client). The period begins running from the original due date of the estate tax return, not from the extended due date if an extension was obtained.

First installment due date: The first installment payment (which is interest only, covering the first interest period) is generally due on the original due date of Form 706, 9 months after the decedent's date of death (verify at IRS.gov). This means the estate does not receive a complete payment holiday even during the deferral period; it must make regular interest-only payments throughout the first 5 years.

All dates and payment period calculations stated above are based on publicly available sources as of July 2026. Verify the current payment schedule requirements, exact due dates, and any grace periods at IRS.gov and under current IRC 6166(a)(3) before advising any client or preparing any payment schedule.

Illustrative Example -- Dates, Amounts, and All Computations Are Illustrative Only

Decedent D died on January 15, 2026. The Form 706 due date (9 months later) would be October 15, 2026 (verify at IRS.gov for the exact due date). The executor timely makes an IRC 6166 election. Under the illustrative schedule (hedge all dates and amounts to IRS.gov and current IRC 6166(a)(3)):

October 15, 2026 through October 15, 2030 (years 1-5): interest-only payments due annually
October 15, 2031 through October 15, 2040 (years 6-15): up to 10 equal annual principal installments plus interest

This example is illustrative only. Do not rely on these dates or this structure as controlling for any specific estate. Compute the actual payment schedule using confirmed dates, the actual deferred tax amount, and current IRS guidance at IRS.gov.

7. Interest Rates: The 2% Tier and the Standard Rate

Caution: Interest Rates Adjust -- Always Verify at IRS.gov Before Advising on the Cost of the Election

The IRC 6166 interest rates are not fixed in absolute terms; the standard rate on deferred estate tax above the 2% threshold amount is set as a percentage of the underpayment rate, which adjusts quarterly. Even the preferential 2% rate tier is subject to conditions and computation rules that must be verified against current IRS guidance. Practitioners should not advise clients on the annual cost of an IRC 6166 election using rates stated in this guide or in any secondary source without first verifying the current applicable rates at IRS.gov. A rate computation made at the time the election is filed may differ significantly from the rate applicable in later years of the installment schedule.

7.1 The Preferential 2% Rate on the "2% Amount"

Under IRC 6601(j) (hedge: verify at IRS.gov and in current IRC text), the portion of deferred estate tax that falls within the "2% amount" carries a preferential reduced rate of 2% per annum. The 2% rate applies only to the first tier of deferred estate tax, measured against an annually adjusted inflation threshold. This preferential rate is one of the most significant financial benefits of the IRC 6166 election and is generally far below commercial borrowing rates in most market environments, making the election economically attractive even beyond its liquidity benefit. Verify the current 2% rate application and the IRC 6601(j)(2) computation at IRS.gov.

7.2 The 2026 Inflation-Adjusted 2% Threshold (Illustrative Only)

The 2% rate applies to the first installment amount of deferred estate tax, up to an inflation-adjusted ceiling. Based on publicly available sources, the 2026 inflation-adjusted 2% threshold is approximately $1.94 million. IMPORTANT: This figure is ILLUSTRATIVE ONLY. The inflation adjustment changes annually. Practitioners must verify the current inflation-adjusted 2% threshold amount at IRS.gov before advising any client on how much of the deferred estate tax will qualify for the preferential 2% rate in any given year. Do not rely on the $1.94 million figure for any specific client computation without independent verification.

7.3 The Standard Rate on Amounts Above the 2% Threshold

Estate tax deferred above the 2% threshold carries interest at 45% of the underpayment rate applicable under IRC 6621 (hedge: verify the current standard rate under IRC 6601(j)(2) and at IRS.gov; never state a specific numeric percentage as a bare figure without hedging to current IRC 6621 and IRS.gov tables). The underpayment rate changes quarterly, so the standard rate on the deferred balance above the 2% threshold will fluctuate over the life of the installment schedule. Practitioners must verify the current underpayment rate and the 45% factor at IRS.gov and under IRC 6621 before advising any client on the expected cost of deferred tax above the 2% threshold. Verify at IRS.gov.

7.4 Deductibility of Interest Paid

Interest paid on deferred estate tax under IRC 6166 may be deductible on Form 1041 (the fiduciary income tax return for the estate) in the year in which the interest is paid (hedge: verify the applicable IRC provisions and IRS guidance governing the deductibility of IRC 6166 interest on Form 1041 at IRS.gov; the deductibility rules may depend on facts specific to the estate and any elections made). This deductibility feature further reduces the effective after-tax cost of the IRC 6166 election in estates where Form 1041 income is generated. Verify the current deductibility rules at IRS.gov before advising on the tax benefit of interest deductions.

8. Security for Deferred Tax: IRC 6324A Special Lien

Warning: Failure to Satisfy the IRC 6324A Lien or Bond Requirement Can Trigger Immediate Default

The security requirements for the IRC 6166 election are not optional. If the estate elects to use the IRC 6324A special lien arrangement and fails to satisfy the lien agreement requirements -- or if the value of the liened assets becomes insufficient to cover the deferred tax obligation -- the IRS may treat the installment arrangement as in default and demand immediate payment of the entire remaining deferred balance. Similarly, if the estate elects to post a bond instead of a lien and fails to maintain adequate bond coverage, the installment arrangement may be accelerated.

Practitioners must monitor the adequacy of the security arrangement throughout the 14-year installment period and should counsel the estate's representative to notify them immediately of any event that might affect the value of liened assets or the adequacy of any bond. Verify the current IRC 6324A lien requirements, default and cure provisions, and IRS procedures at IRS.gov and under Treas. Reg. 20.6324A-1 before establishing or monitoring a security arrangement.

8.1 IRC 6324A Special Lien: Overview

Under IRC 6324A (hedge: verify at IRS.gov and in current IRC text), the estate may satisfy the security requirement for the IRC 6166 election by granting the United States a special lien on specific estate property. This special lien is in lieu of any bond that would otherwise be required. The lien must cover the full amount of the deferred estate tax plus 2 years of interest on that amount (verify the exact coverage requirement at IRS.gov and under Treas. Reg. 20.6324A-1). The lien is recorded against specific identified assets (not a blanket lien on all estate property) and must be established by agreement with the IRS.

8.2 Mechanics of the Lien Agreement

Under Treas. Reg. 20.6324A-1 (hedge: verify that this regulation remains current and has not been amended; check IRS.gov for any updates), the lien agreement must: (a) identify the specific property subject to the lien; (b) be signed by each person who has an interest in the liened property; and (c) be filed with the IRS by the date the election is made. The property subject to the lien must have a value (at the time the agreement is executed) at least equal to the deferred tax plus 2 years of interest. If the value of the liened property subsequently declines below the required coverage level, the estate must provide additional security. Verify all current lien agreement requirements at IRS.gov and under applicable Treasury regulations.

8.3 Bond Alternative

Instead of the IRC 6324A special lien, the estate may post a surety bond meeting the requirements of Treas. Reg. 20.6166-1(d) (hedge: verify that this regulation remains current and that bond requirements have not been modified; check IRS.gov). The bond must be in an amount sufficient to cover the deferred tax and interest. Surety bonds typically involve ongoing premium costs and may require the estate to satisfy creditworthiness requirements with the surety provider. Whether the bond or lien is preferable depends on the specific assets available, their liquidity, and the estate's creditworthiness. Verify the current bond requirements at IRS.gov and under Treas. Reg. 20.6166-1(d).

8.4 Impact on Estate Administration

The IRC 6324A lien attaches to specific identified estate assets and remains in place throughout the installment payment period (up to 14 years). This can complicate estate administration: the liened assets generally cannot be sold, transferred, or further encumbered without IRS consent, because the lien protects the government's security interest. Estates holding illiquid assets (such as real property, partnership interests, or closely held stock) as the liened collateral must plan around this restriction in estate administration and in any ongoing business succession planning. Verify the IRS's current procedures for obtaining consent to dispose of or encumber liened assets at IRS.gov.

9. Acceleration Events Under IRC 6166(g)

Warning: Sale of More Than 50% of the Qualifying Interest Triggers Immediate Full Payment -- Buy-Sell Plans Must Account for This

Under IRC 6166(g)(1)(A) (hedge: verify the current 50% threshold and mechanics at IRS.gov and in current IRC 6166(g) text), if 50 percent or more of the closely held business interest that qualified the estate for the IRC 6166 election is sold, exchanged, or otherwise disposed of, the entire remaining deferred estate tax balance becomes immediately due and payable. This acceleration is triggered by aggregate dispositions over the life of the installment period -- not just by a single transaction. A buy-sell agreement or succession plan that contemplates a sale or transfer of ownership in the qualifying business must be reviewed against this acceleration trigger before it is executed, and practitioners must advise clients and their business advisors to monitor cumulative dispositions against the 50% threshold throughout the installment period.

The practical consequence is significant: a family that elects IRC 6166 to defer estate tax on a closely held business interest and then sells the business (or a controlling interest in it) to fund retirement or effect succession may find that the entire deferred estate tax balance -- which might represent several million dollars -- becomes immediately payable. This can reverse the liquidity benefit the election was designed to provide. Structure any planned disposition with this acceleration trigger explicitly in view, and verify the current acceleration rules at IRS.gov before advising any client.

9.1 The Statutory Acceleration Events: Not an Exhaustive List

IRC 6166(g) (hedge: verify the complete list of acceleration events and their current mechanics at IRS.gov and in the current IRC 6166(g) text) identifies several events that trigger immediate payment of the full remaining deferred estate tax balance. This guide describes the principal acceleration events for practitioner awareness but the list below is NOT exhaustive -- practitioners must verify the complete current list of acceleration events under IRC 6166(g) and IRS.gov before advising any client:

Disposition of more than 50% of the qualifying interest (IRC 6166(g)(1)(A)): Aggregate dispositions exceeding 50% of the qualifying closely held business interest (by value) trigger acceleration. Verify the current threshold and how "disposition" is defined (including gifts, sales, exchanges, and involuntary transfers) at IRS.gov.
Withdrawal of money or property exceeding statutory thresholds (IRC 6166(g)(1)(B)): Aggregate withdrawals of money or other property from the trade or business in excess of specified amounts (hedge: verify current threshold amounts at IRS.gov and under IRC 6166(g)(1)(B)) trigger acceleration. Verify at IRS.gov.
Failure to make a timely installment payment: If an installment payment is not made by its due date, the entire remaining deferred balance may become immediately due, subject to any grace period (hedge: verify the applicable grace period and cure procedures at IRS.gov and under applicable IRS guidance; the grace period rules have changed over time and must be verified against current guidance).
Other acceleration events: IRC 6166(g) contains additional acceleration events beyond those described above. Verify the complete current list at IRS.gov and under current IRC 6166(g) before advising any client that a planned transaction or distribution is safe from acceleration.

9.2 Monitoring Cumulative Dispositions

Because the 50% disposition threshold is measured cumulatively over the entire installment period, a series of small sales or transfers -- none of which individually would cross the 50% threshold -- can collectively trigger acceleration if their aggregate exceeds 50% of the qualifying interest. Practitioners should establish a cumulative disposition tracking protocol for any estate that has elected IRC 6166, documenting every transfer or disposition of the qualifying business interest and computing the running total against the 50% threshold. Verify the current IRS approach to cumulative disposition aggregation at IRS.gov.

9.3 Buy-Sell Agreements and Succession Plans

Buy-sell agreements that are activated at death (for example, an entity purchase arrangement or a cross-purchase agreement funded with life insurance) must be reviewed for their interaction with the IRC 6166(g) acceleration rules. If the buy-sell agreement requires the transfer of more than 50% of the qualifying interest to surviving partners, shareholders, or the entity itself, it may trigger acceleration of the deferred estate tax -- potentially defeating the liquidity benefit of the election entirely. Similarly, a planned succession sale to the next generation or to key employees must be structured and timed with the acceleration rules in mind. Verify at IRS.gov.

10. Interaction with IRC 2032A and Graegin Loans

10.1 IRC 2032A Special Use Valuation

IRC 2032A (hedge: verify at IRS.gov and in current IRC text) allows the executor of a qualifying estate to value qualifying farm and closely held business real property at its current use value rather than its fair market value, potentially reducing the taxable estate significantly. IRC 2032A and IRC 6166 may both be elected for the same estate and the same business; they are complementary strategies. The IRC 2032A reduction in estate value reduces the estate tax due, while IRC 6166 defers payment of the (lower) remaining estate tax. Together, they can substantially address the liquidity problem for qualifying farm and ranch estates and closely held businesses that include real property in the active business.

However, IRC 2032A carries its own recapture rules under IRC 2032A(c) (hedge: verify at IRS.gov): if the qualified heir disposes of the special-use property or ceases the qualified use within a specified period after the decedent's death, a recapture estate tax becomes due. The interaction between IRC 2032A recapture, the IRC 6166 installment payments, and any IRC 6166(g) acceleration events requires careful monitoring. See the IRC 2032A guide in the Related Guides section, and verify all interaction rules at IRS.gov.

10.2 Graegin Loans: Overview

The "Graegin loan" strategy (named for Estate of Graegin v. Commissioner, 56 T.C.M. 387 (1988) -- illustrative citation; verify the current precedential status of this and related cases and all applicable IRS guidance at IRS.gov; the IRS's scrutiny of Graegin loans has increased significantly in recent years) involves borrowing funds from the closely held business entity itself or from a related party (such as a family member or trust) to pay the estate tax, generating a substantial interest deduction on Form 1041 that offsets the income generated by the estate. The strategy can be used as an alternative or complement to IRC 6166.

In the classic Graegin loan, the estate borrows a lump sum from the closely held entity at a fixed interest rate for a long term (for example, 15 to 20 years), uses the proceeds to pay the estate tax in full (avoiding the IRC 6166 election and its acceleration risk), and deducts the prepaid interest or accrued interest on Form 1041. The deduction can generate significant income tax savings that partially offset the estate tax cost. Verify the current IRS treatment of Graegin loans, including the IRS's audit position, the requirements for the interest to be deductible, and any limitations on the deduction, at IRS.gov. IRS scrutiny of Graegin loans has increased; do not rely on the Graegin strategy without current legal research and verification at IRS.gov.

10.3 Graegin Loans vs. IRC 6166: Strategic Considerations

The choice between a Graegin loan (paying estate tax in full and deducting interest) and an IRC 6166 election (deferring estate tax at preferential rates) depends on several factors, including: (a) the estate's and beneficiaries' income tax position and ability to use the interest deduction; (b) the IRC 6166 interest rates relative to commercial borrowing rates; (c) the estate's exposure to IRC 6166(g) acceleration events (particularly planned business sales); (d) the availability and willingness of the entity to make the loan; and (e) IRS audit risk for Graegin loans in the current enforcement environment. Practitioners should model both strategies against the specific facts before recommending one over the other. This is a fact-specific analysis that requires case-by-case professional judgment; verify all applicable rules at IRS.gov.

11. Post-OBBBA Planning: Which Estates Need IRC 6166 After the $15M Exclusion?

11.1 The OBBBA $15 Million Exclusion

The One Big Beautiful Bill Act (OBBBA, Pub. L. 119-21, enacted July 4, 2025) permanently set the basic exclusion amount (BEA) for estate and gift tax purposes at $15 million per person, indexed for inflation. This is an enacted statutory fact. The current indexed amount (which changes annually) must be verified at IRS.gov and in the IRC 2010 guide (see Related Guides); this guide does not state the current indexed BEA as a controlling figure. Portability of the deceased spousal unused exclusion (DSUE) under IRC 2010(c) allows a surviving spouse to add the decedent's unused exclusion to the survivor's own exclusion, potentially shielding up to $30 million of combined value (or the combined indexed exclusion for the applicable year) from estate tax. Verify the current BEA, portability requirements, and any applicable anti-clawback rules at IRS.gov and in the IRC 2010 guide.

11.2 The Post-OBBBA Closely Held Business Candidate Profile

The OBBBA removes most small and medium-sized estates from the estate tax system entirely. The typical post-OBBBA IRC 6166 candidate is an estate with: (a) a gross estate above $15 million per person (or above the combined available exclusion when portability is factored in); (b) more than 35% of the adjusted gross estate represented by a qualifying closely held business interest; and (c) insufficient liquid assets outside the business to pay the estate tax due without liquidating or borrowing against business assets.

In practical terms, this means IRC 6166 planning in the post-OBBBA environment is focused on: large family farms with substantial land values; larger closely held manufacturing, distribution, or service businesses; family limited partnerships and operating companies where growth has pushed total value well above the exclusion; and professional practice entities (subject to the qualification rules for passive assets and the nature of the business interest). The $15 million exclusion filters out many clients who previously faced estate tax, but those who remain -- particularly business owners -- face the same liquidity challenge that IRC 6166 was designed to address.

11.3 OBBBA Made No Changes to IRC 6166

The OBBBA made no direct amendments to IRC 6166. Every aspect of the IRC 6166 election described in this guide -- the 35% test, the definition of closely held business, the aggregation rules, the payment schedule, the interest rate tiers, the lien requirements, and the acceleration events -- continues to operate under pre-OBBBA law. Practitioners should not assume that any OBBBA provision simplifies, modifies, or expands IRC 6166 eligibility or mechanics. Verify the current status of all IRC 6166 provisions at IRS.gov.

11.4 Planning Opportunities in the Post-OBBBA Environment

The significantly higher exclusion means that estates which previously faced estate tax exposure and planned accordingly may no longer need the same strategies. However, for clients whose estates will exceed the $15 million exclusion, the post-OBBBA environment presents several planning considerations: (a) ensure that IRC 6166 eligibility is embedded in the business structure while the client is still alive (monitoring the 35% test against ongoing estate growth and any restructuring); (b) confirm that buy-sell agreements and succession plans are reviewed for IRC 6166(g) acceleration compatibility; and (c) coordinate IRC 6166 with IRC 2032A elections for farm and ranch estates to maximize both deferred payment and valuation reduction benefits. Verify all planning strategies against current IRS.gov guidance and applicable IRC provisions before implementing.

12. Comparison: IRC 6166 vs. IRC 6161 vs. Graegin Loans vs. IRC 453

The following comparison summarizes the principal differences between the four primary estate liquidity strategies available to closely held business estates. All figures and periods in the table are illustrative only; verify all current rates, periods, and qualifications at IRS.gov before advising any client.

Strategy	Mechanism	Eligibility	Duration	Key Risks / Limitations
IRC 6166 Installment Payment	Statutory deferred payment of estate tax attributable to qualifying closely held business interest; interest at preferential 2% rate on first tier, then 45% of underpayment rate (verify IRC 6601(j)(2) at IRS.gov)	35% adjusted gross estate test; qualifying closely held business; executor election on Form 706 by due date	Up to 14 years (5 interest-only plus up to 10 installments); verify IRC 6166(a)(3) at IRS.gov	IRC 6166(g) acceleration events (including 50%+ disposition); IRC 6324A lien/bond requirements; passive asset reduction; no state estate tax deferral
IRC 6161 Extension	Discretionary 12-month extension of time to pay estate tax; IRS approval required; showing of reasonable cause needed	Any estate; no 35% test; IRS discretionary approval; renewable for additional periods in limited circumstances (verify at IRS.gov)	12 months per extension; maximum total extension period limited (verify at IRS.gov)	IRS approval not guaranteed; shorter duration than IRC 6166; no preferential interest rate; no long-term planning vehicle
Graegin Loan	Estate borrows from closely held entity or related party to pay estate tax in full; interest deductible on Form 1041; case-law based (hedge to Estate of Graegin v. Commissioner, 56 T.C.M. 387 (1988); verify current precedent and IRS guidance at IRS.gov)	No 35% test; requires availability and willingness of entity or related party to lend; terms must be bona fide (IRS scrutiny has increased; verify at IRS.gov)	Term of the loan (often 15-20 years); no statutory maximum	IRS audit risk (scrutiny has increased significantly); interest must be bona fide and at arm's length; risk of IRS disallowance of deduction; no statutory interest rate benefit
IRC 453 Installment Sale	Sale of business or assets in exchange for installment obligation; generates cash from which estate tax is paid; income reported as payments received (hedge to IRC 453 and IRS.gov)	No estate tax eligibility test; buyer must be willing to pay on installment terms; may trigger IRC 6166(g) acceleration if closely held interest is sold	Term of installment note; no statutory maximum for estate tax purposes	Capital gain recognition (may be at preferential rates; verify at IRS.gov); interaction with IRC 6166(g) acceleration if IRC 6166 election is also in place; loss of business by estate/heirs

This comparison is a simplified summary for educational purposes. Each strategy has additional nuances, conditions, and risks that are not fully captured in the table above. Verify all current rules, rates, and qualifications at IRS.gov before advising any client on which strategy or combination of strategies is appropriate for a specific estate.

13. Practitioner Checklist

Use this checklist at the outset of any engagement where IRC 6166 may be relevant. All items are hedged to current IRC text and IRS.gov; verify before advising any client. This is a starting point, not a substitute for case-specific analysis.

Confirm gross estate and identify all closely held business interests. Obtain preliminary inventory of the gross estate. Identify each business interest (sole proprietorship, partnership, or corporation) that may qualify as a "closely held business interest" under IRC 6166(b)(1). Note that only interests satisfying the IRC 6166(b)(1) definition (45 or fewer partners/shareholders, OR 20%+ capital/voting interest) are eligible; verify each interest against the current thresholds at IRS.gov.
Compute the adjusted gross estate correctly (after IRC 2053 and IRC 2054 deductions). The 35% test denominator is the adjusted gross estate -- not the gross estate. Deduct all amounts allowable under IRC 2053 (claims, mortgages, debts, administration expenses) and IRC 2054 (losses) to arrive at the adjusted gross estate. Use final or estimated-final figures; do not use preliminary gross estate for the eligibility computation. Verify IRC 2053 and IRC 2054 deductible amounts at IRS.gov.
Apply the passive asset reduction under IRC 6166(b)(8) and (b)(10). Before testing the closely held interest against the 35% threshold, reduce the interest value by the proportionate share of passive assets inside the entity. Obtain an asset inventory from the entity showing active trade or business assets vs. passive assets (excess cash, investment securities, non-operating real property). Verify the current passive asset reduction rules at IRS.gov.
Calculate the closely held interest as a percentage of the adjusted gross estate. After the passive asset reduction, compute the ratio of qualifying closely held interest to adjusted gross estate. Confirm the ratio EXCEEDS more than 35% (exactly 35% does not qualify). If the ratio is close to 35%, obtain a confirmed valuation before filing any election (not a protective election is available if uncertain; see below). Verify the 35% threshold at IRS.gov.
Check the IRC 6166(c) aggregation rules if multiple business interests are involved. If the estate holds interests in more than one closely held business, determine whether those interests can be aggregated. Aggregation of interests in different businesses requires a 20%+ qualifying interest in each (verify at IRS.gov under IRC 6166(c)). If aggregation is needed to meet the 35% threshold, confirm each individual interest qualifies for aggregation.
Confirm election timing: map the Form 706 due date and any 4768 extension. The IRC 6166 election must be made on or before the Form 706 due date (9 months after death) or the extended due date if Form 4768 was filed. Calendar the due date immediately at engagement start. If eligibility is uncertain, file a protective election by the due date rather than missing the deadline while awaiting final valuation. Verify the current Form 706 due date and extension rules at IRS.gov.
Determine whether protective election is needed pending valuation. If the final value of the closely held business interest has not been established (due to ongoing appraisal or valuation dispute), consider filing a protective IRC 6166 election by the Form 706 due date. The protective election preserves the right to the installment arrangement if the qualifying value is ultimately confirmed. Verify the IRS's current protective election procedures at IRS.gov.
Choose the security option: IRC 6324A special lien vs. bond. Determine which security arrangement is preferable given the estate's available assets and creditworthiness. If using the IRC 6324A lien, identify specific estate assets with sufficient value to cover the deferred tax plus 2 years of interest, confirm that all interest holders can sign the lien agreement, and confirm that those assets can remain encumbered for up to 14 years. Verify all lien requirements under Treas. Reg. 20.6324A-1 (or current regulation) at IRS.gov.
Map out the 5-year deferral plus 10-installment schedule (illustrative only). Compute an illustrative payment schedule showing: (a) the 5 annual interest-only payments; (b) the amount of each of the up to 10 principal installments; and (c) the estimated interest at the applicable 2% rate on the first tier and the standard rate on the remainder. Label the schedule "Illustrative Only" and verify all computations against current IRS.gov guidance and IRC 6166(a)(3) before finalizing.
Identify and map all potential IRC 6166(g) acceleration events in the succession plan. Review any existing buy-sell agreements, cross-purchase arrangements, redemption plans, or succession plans that involve the qualifying closely held business interest. Flag any planned transactions that could aggregate to more than 50% disposition of the qualifying interest. Revise any buy-sell or succession structure that would trigger acceleration before the installment period ends. Verify the complete current list of acceleration events at IRS.gov under IRC 6166(g).
Evaluate IRC 2032A interaction for qualifying farm and business real property. If the estate includes qualifying farm or closely held business real property, assess whether an IRC 2032A special use valuation election is also available. A combined IRC 2032A and IRC 6166 strategy can reduce both the tax base and the payment obligation. Note the IRC 2032A recapture risk if qualified use ceases. Verify all IRC 2032A requirements and recapture rules at IRS.gov.
Assess Graegin loan and IRC 453 alternatives or complements. Model the Graegin loan strategy (borrowing from the entity to pay estate tax in full and deducting interest on Form 1041) against the IRC 6166 election to determine which produces a better net outcome given the estate's and beneficiaries' income tax position. Also evaluate whether an IRC 453 installment sale of business assets or interests could generate needed liquidity, factoring in capital gain recognition and the interaction with IRC 6166(g) acceleration. Verify current rules for both strategies at IRS.gov.
Verify state estate tax installment payment provisions separately. IRC 6166 covers only federal estate tax. If the estate is subject to state estate or inheritance tax (several states still impose estate or inheritance taxes with exclusion amounts below the post-OBBBA federal $15 million threshold), check whether the applicable state offers any installment payment election for state estate tax attributable to closely held business interests. Verify the applicable state law with the relevant state revenue department; state provisions are not covered in this guide.

14. Claims Notice

Regulated Claims, Required Verifications, and Limitations

This guide contains statements about IRC 6166 eligibility thresholds, interest rates, payment periods, security requirements, and acceleration events. All such statements reflect publicly available sources as of July 2026 and are subject to change through legislative amendment, IRS rulemaking, regulatory revision, or judicial decision. The following claims are regulated or substantiated claims that practitioners must independently verify before relying on them to advise any client.

Claim or Statement	Applicable Standard	Primary Authority	Required Verification
35% closely held business test (IRC 6166(a)(1))	Closely held business interest must exceed MORE THAN 35% of the adjusted gross estate; no hedge on the percentage threshold itself (statutory)	IRC 6166(a)(1); IRS.gov	Verify current statutory text and any IRS or regulatory guidance on the threshold and computation at IRS.gov
Partnership/shareholder count and percentage thresholds	45 or fewer partners/shareholders OR 20%+ capital/voting interest; hedge both thresholds to current IRC 6166(b)(1)(B)/(C) and IRS.gov	IRC 6166(b)(1)(B) and (C); IRS.gov	Verify current thresholds and how capital/voting interest is measured at IRS.gov; verify family attribution rules under IRC 267(c)
Preferential 2% interest rate on first tier of deferred tax	Reduced 2% rate on the "2% amount" under IRC 6601(j); rate stated as 2% is statutory; verify current application and computation at IRS.gov	IRC 6601(j); IRS.gov	Verify current IRC 6601(j) text, applicable IRS tables, and 2% rate application rules at IRS.gov before advising on the cost of the election
2026 inflation-adjusted 2% threshold (approximately $1.94 million)	ILLUSTRATIVE ONLY; inflation adjustment changes annually; must NOT be used as a controlling figure for any specific client	IRS.gov (current annual adjustment)	Verify the current inflation-adjusted 2% threshold amount at IRS.gov every year; the illustrative $1.94M figure in this guide may not be current
Standard rate on deferred tax above the 2% threshold	45% of the underpayment rate under IRC 6621; rate changes quarterly; never state a specific numeric percentage as a bare figure without hedging	IRC 6601(j)(2); IRC 6621; IRS.gov	Verify current underpayment rate and 45% computation at IRS.gov under IRC 6621 before advising on the cost of deferred tax above the threshold
Payment schedule (up to 14 years; 5-year deferral plus 10 installments)	"Up to 14 years" maximum; hedge to current IRC 6166(a)(3) and IRS.gov; payment schedule details must be verified for each specific estate	IRC 6166(a)(3); IRS.gov	Verify current payment period, installment computation rules, and first-payment due date at IRS.gov; label any illustrative schedules "Illustrative Only"
Holding company / passive asset reduction rules	Passive assets reduce qualifying closely held interest; mechanics hedge to current IRC 6166(b)(8) and (b)(10) and IRS.gov	IRC 6166(b)(8); IRC 6166(b)(10); IRS.gov	Verify current passive asset reduction rules and asset classification standards at IRS.gov before applying the reduction to any specific estate
Acceleration event list under IRC 6166(g)	NOT exhaustive; list in this guide covers principal events only; practitioners must verify the complete current list under IRC 6166(g) and IRS.gov	IRC 6166(g); IRS.gov	Verify the complete current list of acceleration events, thresholds (including the 50%+ disposition trigger), and applicable grace periods at IRS.gov; never rely on this guide's list as exhaustive
Graegin loan interest deductibility	Case-law based (hedge to Estate of Graegin v. Commissioner, 56 T.C.M. 387 (1988)); IRS scrutiny has increased; deductibility is not guaranteed and is subject to IRS challenge	Estate of Graegin v. Commissioner, 56 T.C.M. 387 (1988) (verify current precedential status); IRS.gov	Verify current IRS audit position, deductibility requirements, and applicable case law at IRS.gov and through current legal research before advising on a Graegin loan strategy
Rev. Proc. 2011-42 election procedures	Sets procedural requirements for the IRC 6166 election statement; hedge to "verify any updates at IRS.gov"	Rev. Proc. 2011-42; IRS.gov	Verify that Rev. Proc. 2011-42 remains current and has not been superseded or modified; check IRS.gov for any subsequent guidance before preparing the election statement
State estate tax installment provisions	EXPRESSLY NOT COVERED by this guide; IRC 6166 covers only federal estate tax; state provisions vary widely	Applicable state law (varies by state)	Verify state estate or inheritance tax installment provisions with the applicable state revenue department; do not assume any state mirrors the federal IRC 6166 mechanics

Not Legal Advice

This guide is provided for general informational and educational purposes for tax practitioners and does not constitute legal advice, tax advice, or the establishment of a practitioner-client relationship. The information reflects publicly available sources as of July 2026 and may not reflect subsequent changes to the Internal Revenue Code, Treasury regulations, IRS guidance, or judicial decisions. America's Tax Professionals makes no representation that the information in this guide is complete, current, or applicable to any specific estate's facts. Practitioners are responsible for independently verifying all statements herein at IRS.gov and through current legal research before advising any client. All dollar figures, dates, and rate examples in this guide are illustrative only and must not be used as controlling computations for any specific estate matter.

IRC 6166: Installment Payment of Estate Tax for Closely Held Business Interests