IRC 6654 and 6655: Estimated Tax Underpayment Penalty, Individual and Corporate Safe Harbors, and 2026 Planning

1. Overview and Statutory Basis

The federal income tax is a pay-as-you-go system. Individuals and corporations are required to remit tax throughout the year, either through employer withholding on wages or through direct estimated tax payments. When a taxpayer's prepayments fall short of the required minimum, the IRC responds with an addition to tax -- a form of interest-like charge that compensates the government for the time value of the delayed revenue. Two separate code sections govern this obligation: IRC 6654 for individuals, self-employed taxpayers, and fiduciaries; and IRC 6655 for C corporations.

The IRC 6654 6655 estimated tax underpayment penalty is distinct from the civil penalties under IRC 6651 (failure to file and failure to pay). The IRC 6654 and 6655 additions are computed as part of the return itself, without any required act of IRS assertion or notice and demand. They are not subject to general reasonable cause abatement in the way that IRC 6651 penalties are, and practitioners who treat them as ordinary penalties risk advising clients incorrectly about the available relief paths. Understanding the safe harbor framework is the primary tool for avoiding the addition entirely; understanding the limited waiver mechanisms is the secondary tool for cases where a safe harbor was missed.

This guide addresses the mechanics of IRC 6654 and IRC 6655, the four individual safe harbor tests, the corporate safe harbor framework, the annualized income installment method for both individuals (Form 2210) and corporations (Form 2220), three 2026-specific developments (Notice 2026-03, Notice 2026-24, and the OBBBA IRC 224/225 tip and overtime exclusions), and the practitioner workflow for pre-filing safe harbor analysis and post-filing addition-to-tax response.

For the closely related IRC 6651 failure-to-file and failure-to-pay penalties, which operate on different mechanics and carry full reasonable cause and FTA abatement availability, see the IRC 6651 failure-to-file and failure-to-pay penalty guide.

2. IRC 6654: Estimated Tax Requirements for Individuals

IRC 6654 imposes an addition to tax on any individual who underpays estimated tax for the taxable year. "Individual" for this purpose includes sole proprietors, partners, S corporation shareholders, and any other taxpayer who reports income not subject to withholding, as well as fiduciaries of trusts and estates. The addition is computed separately for each of the four required installments; an underpayment on one installment is not offset by an overpayment on another for purposes of the addition (though overpayments on one installment date can be credited forward if paid early).

Who must pay estimated tax. A taxpayer is not required to make estimated tax payments if the tax shown on the return for the year (after subtracting withholding and refundable credits) does not exceed a de minimis threshold (confirm the current threshold in IRC 6654(e)(1) at IRS.gov). Similarly, no addition to tax applies for a tax year if the prior-year return showed no tax liability and the prior year was a 12-month tax year. These de minimis exceptions are the statutory baseline; all other individual taxpayers with material self-employment or investment income must analyze each installment date against one of the four safe harbors.

Installment due dates. For calendar-year individuals, the four estimated tax installment due dates are: April 15, June 15, and September 15 of the tax year, and January 15 of the following year. If any of these dates fall on a weekend or federal holiday, the due date shifts to the next business day. Each installment covers a specific period of income, but the safe harbor analysis is applied to the cumulative required annual payment allocated across the four dates rather than to quarterly income alone.

The required annual payment. The IRC 6654(d)(1)(A) required annual payment is the lesser of: (a) 90% of the tax shown on the return for the taxable year (the current-year test); or (b) 100% (or 110%, depending on prior-year AGI as discussed in Section 3) of the tax shown on the return for the immediately preceding taxable year (the prior-year test). This required annual payment is then divided equally across the four installment dates to establish the minimum due at each.

3. The Four Individual Safe Harbors Under IRC 6654

An individual avoids the IRC 6654 addition to tax on a given installment if any one of four safe harbor tests is satisfied for that installment. These tests operate independently per installment date, so a taxpayer who misses one test on one date may still satisfy a different test and avoid the addition for that period. Practitioners typically run all four tests and apply whichever produces the lowest required payment for each installment.

Safe Harbor 1: 90% of Current-Year Tax

Under IRC 6654(d)(1)(A), no addition applies if each installment equals or exceeds 22.5% of the tax shown on the current-year return (22.5% being one-quarter of 90%). This is the preferred safe harbor for taxpayers whose income is predictable and roughly equal across quarters. It requires knowing or accurately estimating the full-year tax before the installment due date, which limits its utility for taxpayers with highly variable income.

Safe Harbor 2: 100% of Prior-Year Tax

Under IRC 6654(d)(1)(B), a taxpayer whose prior-year adjusted gross income was at or below the statutory threshold (confirm the current figure in IRC 6654(d)(1)(B) and at IRS.gov; the threshold referenced in guidance is $150,000, or $75,000 for married filing separately) satisfies the safe harbor by paying at least 100% of the tax shown on the prior-year return, divided equally across the four installment dates. This is the most planning-friendly safe harbor because the required payment amount is known at the start of the year without any current-year estimation.

Safe Harbor 3: 110% of Prior-Year Tax (High-AGI Taxpayers)

For taxpayers whose prior-year AGI exceeded the statutory threshold, the prior-year safe harbor requires payment of 110% (rather than 100%) of the prior-year tax. The mechanics are otherwise identical: the required annual payment is 110% of the prior-year tax, divided equally across four installment dates. Practitioners should confirm both the AGI threshold and the 110% multiplier at IRS.gov and in IRC 6654(d)(1)(B) before advising, as these figures are set by statute and should not be applied from secondary sources without verification.

Safe Harbor 4: Annualized Income Installment Method

The annualized income installment method under IRC 6654(d)(2) allows a taxpayer to compute each installment based on the income actually earned through the annualization period, rather than a pro-rata fraction of the full-year tax or prior-year tax. The method is elected on Part II of Form 2210 and requires the taxpayer to compute year-to-date income through each installment period, apply the annualization factor specified in the statute, compute a tentative tax on that annualized income, and then remit a cumulative required percentage of that amount by each due date.

The annualized income method is the primary relief tool for individuals with uneven income: self-employed taxpayers whose business peaks in Q3 or Q4, investors with large Q4 capital gain events, attorneys and consultants with unpredictable fee receipts, and S corporation shareholders whose distributive share is determined late in the year. The method eliminates underpayment additions on early installments that would otherwise be computed based on the full year-end tax even though the corresponding income had not yet been earned.

4. IRC 6655: Estimated Tax Requirements for C Corporations

IRC 6655 establishes an equivalent framework for C corporations. C corporations must make quarterly estimated tax payments to avoid the addition to tax; S corporations are pass-through entities and are not subject to IRC 6655 at the entity level (their shareholders are covered by IRC 6654 individually).

Corporate installment dates. For a calendar-year C corporation, the four installment due dates are April 15, June 15, September 15, and December 15. The corporate December installment date differs from the individual January 15 date. A corporation that misses the December installment has no opportunity to cure before the calendar year closes.

The required corporate annual payment. Under IRC 6655(d), the required annual payment for a C corporation is generally the lesser of (a) 100% of the tax shown on the current-year return or (b) 100% of the tax shown on the prior-year return. Practitioners must confirm the applicable percentages in IRC 6655(d) and at IRS.gov; the specific corporate safe harbor percentages and any special rules for large corporations (as defined in IRC 6655(g)(2)) must be verified against current law. For large corporations, the prior-year safe harbor is generally available only for the first installment, after which the large corporation must recompute based on current-year tax. Confirm the "large corporation" definition and any carryback adjustment rules in IRC 6655(d)(3) at IRS.gov.

Rate for large underpayments. Under IRC 6655(i), if a corporation's underpayment of estimated tax is large (as defined in the statute), an additional 2 percentage points above the standard IRC 6621 rate may apply. Confirm the applicable threshold in IRC 6655(i) at IRS.gov before advising.

5. Annualized Income Installment Method for Corporations: Form 2220

IRC 6655(e) allows C corporations to use the annualized income installment method to compute each quarterly estimated payment. The method is elected and computed on Form 2220 and is the primary planning mechanism for corporations with income that is not evenly distributed across the fiscal year.

Adjusted seasonal installment method. IRC 6655(e)(3) provides an alternative for corporations with a consistent seasonal income pattern: the adjusted seasonal installment method permits each installment to be based on a percentage of the current-year tax derived from the historical seasonal pattern of income, rather than on a mathematical annualization. This method is more complex to compute but can produce smaller installments than annualization for businesses with very pronounced early-year concentration. Confirm the specific mechanics and election requirements in the IRC 6655(e)(3) regulations and Form 2220 instructions before applying.

Form 2220 attachment. A corporation that uses the annualized income installment method must attach Form 2220 to its return. A corporation that does not attach Form 2220 is presumed to have used the regular installment method, and the IRS will compute the addition to tax on that basis. Practitioners who elect the annualized method during the year but fail to attach Form 2220 at filing create an unnecessary collection risk on a liability that was properly planned for.

6. Farmers and Fishermen: IRC 6654(i) and Notice 2026-24

Taxpayers whose gross income from farming or fishing is at least two-thirds of their gross income for the taxable year (or for the preceding taxable year) qualify for the special estimated tax rule under IRC 6654(i). Rather than making four quarterly installments, a qualifying farmer or fisherman may make a single estimated tax payment by March 1 of the following year (or file the return and pay the full tax in full by that date). This one-payment rule is a significant simplification for taxpayers in those industries.

Notice 2026-24: OBBBA-related waiver. The IRS issued Notice 2026-24 to waive the IRC 6654 addition to tax for farmers and fishermen who missed the March 1 one-payment deadline for the applicable tax year due to delays in the instructions for Form 8995, which were revised to reflect the OBBBA tip and overtime exclusions under IRC 224 and IRC 225. Farmers and fishermen who use Form 8995 to compute the qualified business income (QBI) deduction under IRC 199A were unable to accurately complete their returns before March 1 because the updated Form 8995 instructions were not available by that date.

7. OBBBA IRC 224/225 Tip and Overtime Exclusions: 2026 Estimated Tax Traps

The One Big Beautiful Bill Act (OBBBA) enacted IRC 224 and IRC 225, which exclude qualified tips and qualified overtime compensation from federal gross income for the tax years specified in the enacted statute. Practitioners should confirm the exact effective years in IRC 224 and IRC 225 as enacted; the exclusions are expected to apply for tax years within a limited window (confirm the operative years in the statute) and are subject to income limits and other qualifying conditions defined in IRC 224 and IRC 225. Do not rely on a secondary source's description of the effective period without confirming against the statutory text.

Practitioner action steps for OBBBA-affected clients. For every client who reports qualified tips or qualified overtime in 2026: (1) obtain the employer's current Form W-4 and verify that withholding reflects the correct exclusion amount; (2) confirm that the compensation meets the statutory definition in IRC 224 or IRC 225 (as the case may be) -- the exclusions are not automatic for all tips and overtime pay; (3) run both the 90% current-year and 110% prior-year safe harbor calculations and use the lower required amount; (4) if withholding is insufficient to cover the safe harbor, advise the client to make a supplemental estimated tax payment before the next installment due date; and (5) document the analysis and the client's confirmation of the withholding status.

For a full treatment of the IRC 224 and IRC 225 mechanics, the definition of qualified tips and qualified overtime, and the income limitations, see the IRC 401(a) and 401(k) qualified plan requirements guide for interaction with elective deferral and plan compensation definitions affected by the OBBBA. For the excess business loss limitation that further complicates estimated tax projections for business owners, see the IRC 461(l) excess business loss limitation guide.

8. Form 2210: Individual Underpayment Computation

Form 2210 (Underpayment of Estimated Tax by Individuals, Estates, and Trusts) is the computational vehicle for the IRC 6654 addition to tax. Taxpayers are not always required to file Form 2210 with their return; the IRS will generally compute the addition and bill the taxpayer if the return shows an underpayment. However, filing Form 2210 is required (or beneficial) in three situations: (1) the taxpayer is requesting a waiver under IRC 6654(e)(3); (2) the taxpayer is electing the annualized income installment method (Part II); or (3) the taxpayer wants to establish that a shorter period applies to the underpayment rate because the underpayment was paid before the return due date.

Short method vs. regular method. Form 2210 provides a "short method" for taxpayers who did not make any estimated tax payments or who made equal payments on all four due dates. The regular method, which uses a separate schedule for each installment date, is required when payment amounts or timing was uneven, or when electing the annualized income method. Most practitioners should use the regular method to capture all available reductions to the addition.

Waiver request on Form 2210. A taxpayer claiming a waiver under IRC 6654(e)(3) must complete Part II of Form 2210 and submit a statement of facts supporting the waiver request. The IRS evaluates these requests against the narrow statutory standards: unusual circumstances (casualty, disaster) or taxpayer retirement or disability. A general financial hardship argument is not a qualifying ground.

9. IRC 6654 vs. IRC 6655 Estimated Tax Requirements

The table below compares the key features of IRC 6654 (individuals, self-employed, fiduciaries) and IRC 6655 (C corporations). Dollar thresholds and safe harbor percentages reflect current guidance and should be confirmed in the applicable code sections and at IRS.gov before advising.

10. Computing the Underpayment Rate Under IRC 6621

The IRC 6654 and IRC 6655 additions to tax accrue at the underpayment rate established in IRC 6621. That rate is the federal short-term rate, as determined under IRC 1274(d), plus 3 percentage points. The rate is reset quarterly, and daily compounding applies. For corporate large underpayments subject to the additional 2-percentage-point add-on under IRC 6655(i), the effective rate is the short-term rate plus 5 percentage points on the excess underpayment amount (confirm the applicable threshold and mechanics in IRC 6655(i) at IRS.gov).

Because the rate is quarterly, a practitioner computing the addition for a filing must apply the rate in effect during each quarter covered by the underpayment period. A missed April installment will accrue at the Q2 rate for April through June, then at the Q3 rate for July through September, and so on, until the underpayment is paid or the return due date arrives. The IRS posts the applicable underpayment rate each quarter in a Revenue Ruling and at IRS.gov.

Interaction with IRC 6601 interest. The IRC 6654 and 6655 additions to tax are additions to the tax shown on the return. To the extent they are assessed and remain unpaid after the return due date, interest under IRC 6601 begins to run on the unpaid addition. This means a missed installment payment that produces an IRC 6654 addition may itself become the base for IRC 6601 interest if the addition is not paid with the return. Practitioners should advise clients to pay any computed addition along with the return to stop interest accrual on the addition balance.

The IRC 6654/6655 underpayment rate is separate from -- and often equal to -- the underpayment rate for purposes of general tax underpayments under IRC 6601. However, the interaction between the two accrual periods (the estimated tax period from the installment date to the return due date, and the post-due-date IRC 6601 period) means the total interest and addition charge on a missed installment can be computed across two overlapping rate tables. Form 2210 and Form 2220 provide the computational scaffolding to handle this correctly.

11. IRC 55 Corporate AMT (CAMT) and the IRC 6655 Installment Obligation

The corporate alternative minimum tax (CAMT) reinstated by the Inflation Reduction Act of 2022 applies at a 15% rate on the adjusted financial statement income (AFSI) of applicable corporations (generally those with average AFSI exceeding $1 billion over a three-year period, with adjustments for controlled groups; confirm the applicable corporation definition in IRC 55 at IRS.gov). CAMT liability under IRC 55 is a component of the corporation's total tax for the year and therefore increases the IRC 6655 required annual payment.

For tax years beginning after December 31, 2022, a corporation subject to CAMT must include its projected CAMT liability in the computation of each quarterly estimated tax installment. Because AFSI is derived from book income rather than taxable income and requires significant adjustment for tax-book differences, estimating CAMT liability on a quarter-by-quarter basis has proved challenging. This computation difficulty is the factual foundation for Notice 2026-03's waiver of the IRC 6655 addition for CAMT underpayments.

For a detailed treatment of IRC 55 mechanics, the CAMT computation, and the AMT credit under IRC 53, see the IRC 55 individual alternative minimum tax and Form 6251 guide. Note that while the guide title references individual AMT, it covers the CAMT framework as well.

12. Interaction with IRC 6662 Accuracy-Related Penalties

The IRC 6654 and 6655 additions to tax operate independently of the IRC 6662 accuracy-related penalties. IRC 6662 applies to the underpayment of income tax resulting from negligence, substantial understatement, or other accuracy failures, and it requires an affirmative IRS determination. IRC 6654 and 6655, by contrast, are computed on the return as a mathematical consequence of insufficient prepayments, regardless of whether the underlying tax return is accurate.

In practice, a client who underpaid estimated tax and also has a substantial understatement of income tax may face both an IRC 6654 addition (on the underpaid installments) and an IRC 6662 penalty (on the accuracy-related portion of the final underpayment). These two additions are computed on different bases and are not duplicative: the IRC 6654 addition runs from each missed installment date to the return due date, while the IRC 6662 penalty applies to the final underpayment shown on the return after all prepayments are credited. Practitioners should compute both exposures separately when representing a client facing a deficiency determination that also reflects insufficient estimated payments.

For the IRC 6662 accuracy-related penalty mechanics, the reasonable cause and good-faith defense, and the substantial understatement safe harbor for disclosed positions, see the IRC 6662 accuracy-related penalties guide.

13. Frequently Asked Questions

14. Practitioner Workflow: Pre-Filing Safe Harbor Analysis and Post-Filing Response

Step 1: Identify the applicable code section and taxpayer type. Determine at the outset whether the client is subject to IRC 6654 (individual, SE taxpayer, or fiduciary) or IRC 6655 (C corporation). The two sections have different installment schedules, different safe harbor percentages, and different waiver paths. Conflating the two produces incorrect computations.

Step 2: Pull prior-year tax and AGI data. For an individual client, obtain the tax shown on the prior-year return (Form 1040, line 24 or the equivalent, reduced by credits as appropriate for the safe harbor computation) and the prior-year AGI. Confirm the AGI against the applicable threshold in IRC 6654(d)(1)(B) to determine whether 100% or 110% applies. For a corporate client, obtain the prior-year tax from the Form 1120. Document these figures before computing the safe harbor minimum.

Step 3: Run all applicable safe harbors. For an individual, compute: (a) 90% of the projected current-year tax divided by four; (b) 100% (or 110%) of the prior-year tax divided by four; and (c) the annualized income installment if income is uneven. Use the lowest quarterly result. For a corporation, compute both the prior-year and current-year safe harbors and elect the annualized income installment method on Form 2220 if the income pattern warrants it.

Step 4: Check withholding adequacy before each installment date. Withholding is credited ratably across installment dates for safe harbor purposes (with limited exceptions). If a client's withholding is below the pro-rata share of the required annual payment, a supplemental estimated payment is needed to cover the gap before the next installment date. For OBBBA-affected clients, verify that the employer's adjusted withholding actually reflects the client's qualifying exclusion amount, not an assumed exclusion that the client's compensation may not satisfy.

Step 5: Attach the correct forms at filing. Attach Form 2210 if the individual is electing the annualized income installment method, requesting a waiver, or has uneven payment timing. Attach Form 2220 for any corporation using the annualized income or adjusted seasonal installment method. Failing to attach Form 2220 when the method has been used leaves the IRS to compute the addition on an incorrect basis.

Step 6: Respond to IRS computed addition-to-tax notices. If the IRS issues a notice computing the IRC 6654 or 6655 addition: (a) verify the IRS's prior-year tax figure and the withholding credit allocation used in the computation; (b) run the alternative safe harbor calculations to determine if any safe harbor the client was entitled to was not applied; (c) if the annualized income method was not used but would have produced a lower addition, file Form 2210 or Form 2220 (as applicable) to claim the method retroactively; and (d) if a statutory waiver under IRC 6654(e)(3) or an administrative waiver (Notice 2026-03 or 2026-24) applies, submit a written request with supporting documentation to the IRS service center. Do not submit a general reasonable cause request for the IRC 6654 or 6655 addition; such requests will be denied, and they are not the correct vehicle for these additions.

For penalty response strategy and abatement procedures applicable to the related IRC 6651 and IRC 6662 penalties, see the IRC 6662 accuracy-related penalties guide.

15. Claims and Limitations Notice