IRC 2001 Estate Tax Computation, Tentative Tax, and Unified Credit: Form 706 Practitioner Guide

Overview: The Federal Estate Tax and the Unified Transfer Tax System

The federal estate tax, imposed under IRC 2001 in Chapter 11 of the Internal Revenue Code, is a transfer tax on the privilege of passing wealth at death. It does not function in isolation. Congress designed it as one leg of a unified transfer tax system that includes the federal gift tax (Chapter 12) and the generation-skipping transfer (GST) tax (Chapter 13). The unification is accomplished through a single graduated rate table, a single applicable exclusion amount, and a computation method that aggregates lifetime gifts and the taxable estate to ensure all transfers are taxed at the same marginal rate.

For practitioners preparing Form 706 (United States Estate (and Generation-Skipping Transfer) Tax Return), the core mechanics live in three provisions:

• IRC 2001(a): imposes the tax on the taxable estate.
• IRC 2001(b): specifies the tentative tax computation, incorporating adjusted taxable gifts and the credit for prior gift taxes.
• IRC 2010: grants the unified credit against estate tax and defines the applicable exclusion amount.

The One Big Beautiful Act (OBBBA) reshaped the landscape materially. It permanently raised the basic exclusion amount to $15 million per person (indexed for inflation; verify the current indexed 2026 amount at IRS.gov and consult independent counsel, as these provisions are recently enacted and implementation guidance may be pending). This change avoids the sunset that would have reduced the exclusion under pre-OBBBA law and makes Form 706 a tax-event return for far fewer estates than in prior years. For large estates and complex transfers, however, the underlying mechanics of IRC 2001 remain analytically demanding territory.

IRC 2001(a): Imposition of the Estate Tax and the Taxable Estate

IRC 2001(a) is a single operative sentence: it imposes a tax on the transfer of the taxable estate of every decedent who is a citizen or resident of the United States. The statute reaches the entire taxable estate without geographic limitation for US citizens and residents; nonresident alien decedents are subject to a separate regime under IRC 2101 through 2108, which taxes only US-situs property. This guide addresses the IRC 2001 regime for citizens and residents.

The Gross Estate

The starting point for computing the taxable estate is the gross estate, valued as of the date of death (or the alternate valuation date under IRC 2032 if elected). The gross estate includes:

• All property in which the decedent had an interest at death (IRC 2033), valued at fair market value.
• Certain dower and curtesy interests (IRC 2034).
• Transfers made during life in which the decedent retained the right to income, use, or enjoyment, or retained a power to alter, amend, revoke, or terminate (IRC 2036, 2037, 2038).
• Transfers within three years of death that are included under IRC 2035, primarily transfers of IRC 2036-2038 interests and life insurance within three years.
• Annuities and survivorship interests (IRC 2039, 2040).
• Powers of appointment exercised or releasable (IRC 2041).
• Life insurance proceeds on policies owned by the decedent or includable under IRC 2042.
• Certain qualified terminable interest property (QTIP) previously elected under IRC 2044.

Allowable Deductions and the Taxable Estate

The taxable estate equals the gross estate reduced by the deductions allowable under IRC 2051 through 2058. The principal deductions are:

• IRC 2053: funeral expenses, administration expenses, claims against the estate, and mortgages and indebtedness.
• IRC 2054: losses incurred during administration from fires, storms, shipwrecks, and other casualty losses and theft.
• IRC 2055: the charitable deduction, for bequests to qualifying public charities, private foundations, and governmental entities.
• IRC 2056: the marital deduction, for qualifying transfers to a surviving spouse, including QTIP trusts and qualified domestic trusts (QDOTs) for noncitizen spouses.
• IRC 2058: state death taxes actually paid (subject to the limitations of that section).

The resulting figure, the taxable estate, is the foundation for the IRC 2001(b) tentative tax computation. Verify the current scope of each deduction and any applicable limitations at IRS.gov before preparing Form 706.

IRC 2001(b): Tentative Tax Computation and the Rate Table

IRC 2001(b) prescribes a four-step cumulative computation that integrates the decedent's lifetime taxable gifts with the current taxable estate. The mechanics ensure that prior gifts do not escape the top marginal rate by being isolated in lower brackets:

Step-by-Step Computation Under IRC 2001(b)

1. Compute the cumulative transfer tax base. Add the taxable estate (from Step 1 above) to the decedent's total adjusted taxable gifts (post-December 31, 1976, taxable gifts not included in the gross estate). The sum is the cumulative transfer tax base.
2. Apply the rate table to the cumulative base. Using the unified rate schedule under IRC 2001(c), compute the tentative tax on the entire cumulative base (taxable estate plus adjusted taxable gifts). This is the gross tentative tax on all wealth transferred.
3. Subtract the tentative tax on adjusted taxable gifts alone. Compute a second tentative tax using the same IRC 2001(c) rate table applied only to the adjusted taxable gifts (at the rates in effect at death, per IRC 2001(b)(2)). Subtract this amount from Step 2. The resulting figure is the tentative estate tax attributable to the current taxable estate.
4. Apply credits. Subtract the unified credit under IRC 2010 and any other allowable credits (including the credit for foreign death taxes under IRC 2014 and the credit for taxes on prior transfers under IRC 2013) to arrive at the net estate tax due.

The Rate Table Under IRC 2001(c)

The unified rate table under IRC 2001(c) is graduated, with rates ranging from 18% on the first $10,000 of taxable transfers up to 40% on taxable transfers above $1,000,000. For estates where the applicable exclusion amount absorbs the lower brackets (which the $15 million exclusion will do for almost all estates), the effective marginal rate on the portion above the exclusion is 40%. The rate table applies to the cumulative base, not just the taxable estate in isolation, which is why the Step 3 subtraction of the tentative tax on prior gifts is necessary to avoid taxing the same transfers twice. Verify the current IRC 2001(c) rate table at IRS.gov before computing the tentative tax for any estate.

Adjusted Taxable Gifts: Building the Cumulative Transfer Tax Base

Under IRC 2001(b), "adjusted taxable gifts" means the total amount of the decedent's taxable gifts made after December 31, 1976, other than gifts that are includible in the decedent's gross estate. The "other than" exclusion prevents double-counting: gifts pulled back into the gross estate under IRC 2035 (gifts of life insurance within three years of death) or IRC 2036 through 2038 (retained interest transfers) are already in the taxable estate, so they must not also appear in adjusted taxable gifts.

What Qualifies as a Taxable Gift for This Purpose

A taxable gift for purposes of IRC 2001(b) is a transfer that was reportable on Form 709 after subtracting the annual exclusion under IRC 2503(b), the IRC 2503(e) tuition and medical exclusions, and any marital or charitable deductions. It does not reduce for the unified credit actually applied -- the credit reduces the tax, not the gift amount. This distinction matters: the cumulative base under IRC 2001(b) includes the full taxable gift amounts even if no gift tax was actually paid because the unified credit absorbed the liability.

Audit Risk in the Adjusted Taxable Gifts Figure

The IRS has three years from the filing date of Form 706 to audit estate tax returns, but there is no statute of limitations on the undervaluation of gifts if the gift was not adequately disclosed on Form 709. If a gift was not reported (or not adequately disclosed) on Form 709, the IRS may revalue it for purposes of IRC 2001(b) even after the gift tax period is closed. Adequate disclosure on Form 709 is therefore a prerequisite to closing the gift valuation for both gift tax and estate tax purposes. Verify current disclosure standards and statute of limitations rules at IRS.gov.

IRC 2001(b)(2): Credit for Gift Taxes Previously Paid

The subtraction mechanism in IRC 2001(b) also addresses the rate-harmonization issue for gifts made under a different rate table than the one in effect at death. Under IRC 2001(b)(2), when computing the Step 3 subtraction (the tentative tax on adjusted taxable gifts alone), the computation uses the rates in effect at the time of death -- not the rates that were in effect when the original gifts were made. This prevents an estate from benefiting from lower historical rates on prior gifts.

Pre-1977 Gifts and the IRC 2012 Credit

For gifts made before January 1, 1977 (under the pre-unified gift tax system), the Code does not use the IRC 2001(b) subtraction mechanism. Instead, IRC 2012 provides a separate credit for gift taxes actually paid on pre-1977 gifts. This credit operates differently from the IRC 2001(b) netting: it is a direct credit for taxes paid, capped at the amount of estate tax attributable to including the gift in the estate. In practice, pre-1977 gifts are now rare in active estates, but practitioners advising elderly decedents or reviewing estates of persons who died decades ago may encounter them. Verify current IRC 2012 credit mechanics at IRS.gov.

Interaction with the Unified Transfer Tax System

The combined effect of IRC 2001(b) is that the estate tax computation nets out the prior gift tax that would have been paid (at current rates) on adjusted taxable gifts, leaving only the incremental estate tax on the taxable estate as the remaining liability before credits. When the unified credit under IRC 2010 is then applied, the result is that the credit absorbed during lifetime gift tax is effectively "credited" at the estate level through the rate-harmonization netting -- neither the estate nor prior gift taxes are double-counted within the unified system. This is the conceptual foundation that makes the gift tax and estate tax a single integrated system rather than two independent taxes.

IRC 2010: Unified Credit Against Estate Tax and the Applicable Exclusion Amount

IRC 2010(a) allows a credit against the estate tax equal to the applicable credit amount. The applicable credit amount under IRC 2010(c)(1) is the amount of the tentative tax that would be imposed under IRC 2001(c) on the applicable exclusion amount. In plain terms, the credit exactly offsets the estate tax on a taxable estate (plus adjusted taxable gifts) up to the applicable exclusion amount.

Components of the Applicable Exclusion Amount

The applicable exclusion amount under IRC 2010(c) has two components:

• Basic exclusion amount (BEA): The per-person exclusion set by statute and indexed for inflation. The OBBBA permanently set this at $15 million (indexed for inflation; verify the current 2026 indexed amount at IRS.gov and consult independent counsel, as these provisions are recently enacted and implementation guidance may be pending).
• Deceased spousal unused exclusion (DSUE): The unused portion of a predeceased spouse's applicable exclusion amount, portable to the surviving spouse under IRC 2010(c)(2) if the portability election is made. The DSUE increases the surviving spouse's applicable exclusion above the BEA. Discussed further in the Portability section below.

Reduction for Lifetime Unified Credit Usage

The unified credit is shared between the gift tax (IRC 2505) and the estate tax (IRC 2010). Every dollar of applicable exclusion amount used to shelter a lifetime taxable gift from gift tax reduces the applicable exclusion amount available at death dollar for dollar. The estate tax return must account for all lifetime credit usage. If the decedent used $5 million of applicable exclusion amount during life (sheltering $5 million of taxable gifts), only the remaining exclusion amount (BEA minus $5 million used, plus any DSUE) is available at death. Verify current credit-tracking mechanics and the interaction between IRC 2505 (gift tax credit) and IRC 2010 (estate tax credit) at IRS.gov.

OBBBA: Permanent $15 Million Exemption and Sunset Avoidance

Before the Tax Cuts and Jobs Act (TCJA) of 2017, the basic exclusion amount was $5 million (indexed from a 2010 base). The TCJA temporarily doubled the BEA to approximately $10 million (indexed from a 2010 base) for tax years 2018 through 2025, but the doubled amount was set to sunset after December 31, 2025, reverting to the pre-TCJA inflation-adjusted level (which research indicates would have been approximately $7 million for 2026; verify the applicable figure at IRS.gov).

The OBBBA permanently raised the BEA to $15 million per person (indexed for inflation beginning after 2025; verify the current indexed 2026 amount at IRS.gov and consult independent counsel, as these provisions are recently enacted and implementation guidance may be pending). This single change has the following practical consequences for practitioners:

• Estates below the BEA (approximately $15 million for a single decedent, and up to approximately $30 million for a married couple using portability) will owe no federal estate tax.
• The sunset planning urgency that drove many clients to accelerate gifts before December 31, 2025, is resolved. Transfers made to use the elevated TCJA exemption before sunset are now subject to the same permanent level under the OBBBA.
• Anti-clawback regulations under IRC 2010(g) -- finalized by Treasury for TCJA-period gifts made 2018-2025 -- remain relevant for estates of persons who died before the OBBBA's effective date. Verify the current status of those regulations and any OBBBA interaction at IRS.gov and consult independent counsel.
• For larger estates ($30 million and above for a married couple), estate tax planning, trust structuring, and valuation discounts remain important. The rate on the taxable portion above the exclusion is still 40%.

Portability: Deceased Spousal Unused Exclusion Under IRC 2010(c)(5)

Portability, enacted as part of the Tax Relief, Unemployment Insurance Reauthorization, and Job Creation Act of 2010 and made permanent by the American Taxpayer Relief Act of 2012, allows a surviving spouse to carry over the unused portion of a predeceased spouse's applicable exclusion amount. The vehicle is the deceased spousal unused exclusion (DSUE).

Computing the DSUE

The DSUE of the first-to-die spouse is the lesser of:

• The basic exclusion amount in effect in the year of the predeceased spouse's death, OR
• The excess of the applicable exclusion amount of the predeceased spouse over the sum of the taxable estate of the predeceased spouse and the adjusted taxable gifts of the predeceased spouse made after the date of the predeceased spouse's last Form 706.

In plain terms: the DSUE is the predeceased spouse's unused exemption capacity -- the portion of the exclusion the predeceased spouse did not consume through lifetime gifts or the taxable estate.

The Portability Election

Portability is not automatic. The executor of the predeceased spouse's estate must make a portability election by filing a timely Form 706. Even if no estate tax is owed because the estate is below the filing threshold, a Form 706 must be filed if the surviving spouse wants to preserve the DSUE. Under the simplified procedure in Rev. Proc. 2022-32, estates that were not otherwise required to file Form 706 may file a late portability election within five years of the decedent's death (for decedents dying on or after January 1, 2011). Verify the current Rev. Proc. 2022-32 deadline and any extensions or modifications at IRS.gov before advising on a late portability election.

Limitations on DSUE Use

Key practical limitations apply to DSUE use by the surviving spouse:

• Only the DSUE of the most recently deceased spouse is available. A surviving spouse's prior-deceased first spouse's DSUE is replaced by the DSUE of a subsequently deceased second spouse, even if the second spouse's DSUE is smaller.
• The DSUE is not indexed for inflation. A DSUE of $10 million from a spouse who died in 2022 remains at $10 million when the surviving spouse uses it, even if the BEA has increased by the time of the surviving spouse's death or lifetime gift.
• The IRS may audit the predeceased spouse's estate tax return in connection with assessing the surviving spouse's estate tax, specifically to verify the DSUE amount claimed. This audit right extends beyond the normal statute of limitations.
• For non-citizen surviving spouses, portability is not available; the applicable exclusion may flow through a qualified domestic trust (QDOT) under IRC 2056A rather than directly.

Form 706: Filing Requirements, Due Date, and Extension

Form 706 (United States Estate (and Generation-Skipping Transfer) Tax Return) is the return on which the executor computes the estate tax under IRC 2001, applies the unified credit under IRC 2010, and makes or revokes elections including portability, special use valuation under IRC 2032A, and QTIP elections under IRC 2056(b)(7).

Filing Threshold

Form 706 is required when the decedent's gross estate, plus adjusted taxable gifts, plus the specific exemption allowable under IRC 2521 (for gifts made before 1977), exceeds the applicable exclusion amount in the year of death. With the OBBBA permanent exclusion at approximately $15 million (verify the current indexed amount at IRS.gov), the filing threshold for a single decedent is substantially higher than under pre-TCJA law. However, Form 706 is also required to make the portability election, regardless of whether any estate tax is due.

Due Date

Form 706 is due nine months after the date of the decedent's death. For example, for a decedent who died on March 1, 2026, the return is due December 1, 2026. Verify the specific due date calculation and any calendar-adjusted deadlines at IRS.gov.

Extension of Time to File

Form 4768 (Application for Extension of Time To File a Return and/or Pay U.S. Estate (and Generation-Skipping Transfer) Taxes) provides an automatic six-month extension of time to file, extending the deadline from nine to fifteen months after the date of death. This extension is for time to file only; it does not extend the time to pay the estate tax. Tax owed must be paid by the original nine-month deadline, and interest accrues from that date on any unpaid balance. A separate extension for time to pay may be granted in limited circumstances under IRC 6161. Verify current extension procedures, payment deadlines, and interest rules at IRS.gov.

Elections Made on Form 706

Form 706 is the vehicle for several time-sensitive elections that cannot be made after the return is filed (or after the extension period), including:

• Portability of DSUE to surviving spouse (IRC 2010(c)(5)).
• Alternate valuation under IRC 2032 (election to value assets six months after death instead of at death, available only if it reduces both the gross estate and the estate tax).
• Special use valuation under IRC 2032A (discussed in the next section).
• QTIP election under IRC 2056(b)(7) for the marital deduction on qualifying transfers to a surviving spouse through a trust.
• Section 6166 installment payment election (if the estate consists of a closely held business interest meeting the percentage test under IRC 6166(a), the executor may elect to pay estate tax in installments over up to fourteen years).

Verify all elections, their timing requirements, and revocability rules at IRS.gov before filing Form 706.

IRC 2032A: Special Use Valuation and its Interaction with the Estate Tax

IRC 2032A allows the executor to elect to value qualifying real property used in a closely held farm or other trade or business at its special use value (the value for its actual use) rather than at its fair market value (FMV) -- which typically reflects the property's highest and best use. The difference between FMV and special use value can be substantial for farm land that is valued highly for development but farmed at much lower agricultural income rates.

Eligibility Requirements

To qualify for IRC 2032A special use valuation, a number of conditions must be met (verify all requirements at IRS.gov):

• The decedent was a US citizen or resident.
• The real property is used for a qualifying use (farming or a closely held business) at the date of the decedent's death and has been used for a qualifying use for at least five of the eight years preceding death.
• The property passes to a qualifying heir (defined in IRC 2032A(e)(1)).
• The value of the qualifying property (real and personal) equals at least 50% of the adjusted value of the gross estate.
• The value of the qualifying real property alone equals at least 25% of the adjusted value of the gross estate.

Reduction Cap and Recapture

The aggregate reduction in the value of qualifying real property under IRC 2032A is capped at an indexed amount (research indicates the 2026 cap is approximately $1,390,000; verify the current indexed cap at IRS.gov before computing the allowable reduction). If the qualifying heir disposes of the property or ceases the qualifying use within ten years of the decedent's death, a recapture tax equal to the estate tax benefit obtained through the special use valuation is imposed under IRC 2032A(c).

Interaction with the OBBBA Permanent Exemption

With the OBBBA basic exclusion amount at approximately $15 million, the estate tax savings from IRC 2032A are reduced for many farm estates that previously relied on the special use valuation to bring the taxable estate below the exclusion. For larger farm estates or those with substantial non-real-estate assets, the valuation reduction may still provide meaningful tax savings. Practitioners should model both the IRC 2032A election and the no-election alternative to determine the net tax benefit, taking into account the IRC 6166 installment payment election as well. Verify current applicable exclusion amounts and the interaction with IRC 2032A at IRS.gov.

IRC 1014: Step-Up in Basis and Post-OBBBA Planning Implications

IRC 1014(a) provides that the basis of property acquired from a decedent is its fair market value at the date of death (or the alternate valuation date, if elected). This step-up (or step-down, for depreciated property) in basis is one of the most significant income tax benefits in the Code, and it interacts powerfully with the estate tax in post-OBBBA planning.

How the Step-Up Works

Under IRC 1014(a)(1), property included in the decedent's gross estate under Chapter 11 receives a new basis equal to its date-of-death FMV. If the FMV at death exceeds the decedent's adjusted basis, the heir steps up to the higher FMV and eliminates the built-in gain on all appreciation accumulated during the decedent's lifetime. A beneficiary who sells the property immediately after inheriting it typically recognizes little or no capital gain. The step-up applies to capital assets, real estate, closely held business interests, and most other assets in the gross estate.

Property Not Eligible for Step-Up

Certain property does not receive an IRC 1014 step-up:

• Income in respect of a decedent (IRD) under IRC 691 -- for example, installment notes, accrued but unpaid compensation, IRA and retirement plan accounts, and S corporation income earned but not distributed. IRD assets carry their embedded income tax liability to the beneficiary.
• Property acquired by the decedent by gift within one year of death, where the property passes back to the donor or the donor's spouse under IRC 1014(e), retains the estate's basis rather than receiving a fresh step-up (an anti-abuse rule).

Post-OBBBA Planning: Retain vs. Gift Appreciated Assets

With the OBBBA raising the estate tax exclusion to approximately $15 million per person, the estate tax cost of retaining appreciated assets until death is eliminated for most families. The income tax benefit of the IRC 1014 step-up therefore tips the analysis firmly toward retention for most moderate-wealth clients. For a client with a $10 million estate consisting largely of appreciated stock, gifting the stock during life eliminates the estate tax (but the estate was below the exclusion anyway) while also transferring the carryover basis problem to the donee under IRC 1015 -- the donee inherits the low adjusted basis and will owe capital gains tax on the full appreciation when the stock is sold. The same client who retains the stock until death gives heirs the full step-up and no income tax on the prior appreciation.

For very large estates where the estate tax applies above the exclusion, the cost-benefit analysis is more nuanced: the estate tax rate on the appreciation retained is 40%, while the long-term capital gains rate is 20% (plus net investment income tax for high earners). Verify current capital gain and net investment income tax rates at IRS.gov before advising on retain-vs.-gift decisions.

Interaction with IRC 2032A Special Use Property

For property elected under IRC 2032A special use valuation, the basis under IRC 1014(a) is the special use value, not the FMV. If the property is later sold at a price above the special use value (but below or equal to the FMV at death), the difference between the sale price and the special use value basis is a taxable gain. Heirs who plan to sell special use property shortly after the estate is settled should model both the IRC 2032A tax savings and the increased basis gap before making the election. Verify basis rules for IRC 2032A property at IRS.gov.

State Estate Tax Considerations

This guide is a federal tax reference. Practitioners must also be aware that many states impose their own estate or inheritance taxes at lower exemption thresholds than the federal exclusion. As of the date of this guide, states including Massachusetts, Oregon, Washington, Maryland, Connecticut, New York, Illinois, and Hawaii, among others, impose state estate taxes with exemptions ranging from approximately $1 million to $7 million. Because the OBBBA raised the federal exclusion dramatically, estates that owe no federal estate tax may still owe significant state estate tax. State exemptions, rates, and available deductions differ materially from the federal rules. Practitioners and clients should consult state tax counsel for a state-specific analysis in every estate involving real property or domicile in a state with an estate or inheritance tax.

Illustrative Computation: Estate Tax on a $20 Million Estate

Note: All figures below are illustrative only. They use assumed values for educational purposes and do not represent any specific taxpayer's situation. Verify all applicable exclusion amounts, rate tables, and indexed figures at IRS.gov before preparing any return or advising any client.

Comparison Table: Key Estate Tax Parameters Before and After OBBBA

The following table summarizes key estate tax parameters across three legislative periods. All figures must be verified at IRS.gov; they are presented for educational context only and are subject to annual indexing adjustments and any post-OBBBA implementation guidance.