The annualized income installment method lets you size each quarterly estimated tax payment to the income you had actually received by that deadline, instead of paying four equal amounts based on a full-year projection. It’s the tool for reducing or eliminating the underpayment penalty when your earnings are backloaded or seasonal, and you claim it by attaching Schedule AI of Form 2210 to your return.
Who Benefits From This Method
The IRS default assumes you earn at a steady pace and expects roughly equal payments on each of the four estimated tax due dates. That works for salaried filers with predictable withholding. It penalizes people whose income arrives in bursts: a landscaper whose revenue runs from April through October, an investor who sells appreciated stock in November, a consultant paid in a single year-end lump sum. Under the equal-installment assumption, those taxpayers underpay the first quarter or two even though the money hasn’t arrived yet.
Annualizing fixes that mismatch. You recalculate the required payment at each deadline using only the income received through that point, so a near-zero first quarter produces a near-zero first required payment. IRS Publication 505 lays out the approach for justifying unequal installments.1Internal Revenue Service. Publication 505 (2026), Tax Withholding and Estimated Tax
Two rules to know before you commit. The method is optional, and you can elect it after the fact when you file. But if you use it for one payment period, you have to use it for all four.2Internal Revenue Service. Instructions for Form 2210
Check the Safe Harbors First
Before working through Schedule AI, see whether you already avoid the penalty. You generally owe an underpayment penalty only if you owe more than $1,000 at filing and you missed the safe harbors during the year. You satisfy a safe harbor if your withholding and estimated payments cover at least 90 percent of your current-year tax or 100 percent of last year’s tax, whichever is smaller.3Internal Revenue Service. Topic No. 306, Penalty for Underpayment of Estimated Tax
The prior-year threshold climbs to 110 percent if your adjusted gross income in the prior year exceeded $150,000, or $75,000 if you file married filing separately.4Internal Revenue Service. Underpayment of Estimated Tax by Individuals Penalty If prior-year withholding and payments already put you over that bar, annualizing gains you nothing.
The method earns its keep when neither safe harbor was met and the shortfall traces to timing rather than to underpaying overall. The penalty is calculated separately for each installment due date, so a single short quarter can generate a charge even if you paid enough in total by year-end.
The Records You Need for Each Period
Annualizing runs on precise, period-by-period figures. You can’t total the year and divide by four. Each of the four columns on Schedule AI covers a specific cumulative window: January 1 through March 31, January 1 through May 31, January 1 through August 31, and the full year.5Internal Revenue Service. 2025 Instructions for Form 2210 The periods are three, five, eight, and twelve months long, not equal quarters.
For each window you need the cumulative totals of:
- Gross income actually received through that date, dated by when funds were deposited or the transfer settled, not when the work was performed.
- Deductions through that date, either the standard deduction (same amount in every period) or a running total of itemized items like mortgage interest and medical expenses.
- Business expenses tallied by transaction date, not payment date.
- Federal tax already paid through that date, including withholding from wages or pensions and any estimated payments already submitted.
The point of this detail is verification: the IRS is letting you show that a lower early-quarter payment matched lower early-quarter income. Tagging income and expenses by month as they happen is far easier than reconstructing the same information at filing time.
How the Calculation Works
The mechanics are less intimidating than the worksheet looks. For each period, take the income actually received, project it to a full year, calculate the tax on that projected annual amount, and then take the portion that should have been paid by the end of that period.
Annualization Multipliers
Each period’s cumulative income is multiplied to produce a full-year equivalent:1Internal Revenue Service. Publication 505 (2026), Tax Withholding and Estimated Tax
- First period (3 months): multiply by 4
- Second period (5 months): multiply by 2.4
- Third period (8 months): multiply by 1.5
- Fourth period (12 months): multiply by 1
If you earned $30,000 through March, the first-period multiplier of 4 projects a $120,000 annual pace. Apply the tax rates, deductions, and credits to that $120,000 as if it were your full annual income to get a hypothetical annual tax.
Applicable Percentages
You then take the cumulative share of that projected tax that should have been paid by the period’s deadline. The statute sets the percentages:6Office of the Law Revision Counsel. 26 USC 6654 – Failure by Individual to Pay Estimated Income Tax
- First installment: 22.5 percent
- Second installment: 45 percent
- Third installment: 67.5 percent
- Fourth installment: 90 percent
Each figure is cumulative, so the required payment for any single quarter is the applicable percentage of that period’s projected tax minus what you were required to pay in prior installments. If the first-period calculation gives $4,500 (22.5 percent of a $20,000 projected tax) and the second period gives $13,500 cumulative (45 percent of a $30,000 projected tax), the second-quarter required payment is $9,000.
Self-Employment Tax Within the Calculation
Self-employment tax gets its own line-by-line computation within Schedule AI. The Social Security portion applies only to earnings up to the annual wage base ($184,500 for 2026), after which only the Medicare portion continues.7Social Security Administration. Contribution and Benefit Base Handling it inside the annualized schedule keeps you from overstating Social Security tax when cumulative earnings cross the cap partway through the year.
Filing Schedule AI With Form 2210
Schedule AI is a multi-column worksheet, one column per cumulative period. You work each column top to bottom: enter actual income for the period, apply the multiplier, calculate the projected tax, and apply the applicable percentage to get the required cumulative payment by that deadline.5Internal Revenue Service. 2025 Instructions for Form 2210
The schedule also folds in additional taxes that apply to your situation. The instructions direct you to include alternative minimum tax and household employment taxes on the same lines as the regular tax computation.5Internal Revenue Service. 2025 Instructions for Form 2210 Nanny or housekeeper employment taxes come into the calculation unless you had no federal withholding and wouldn’t otherwise need to make estimated payments.
The results feed into the main body of Form 2210, which compares your required installments against what you actually paid on each due date. Because the penalty runs separately for each date, you can end up with a penalty for one quarter and none for another. Attach Parts I, II, III, and Schedule AI to your Form 1040 when you file.5Internal Revenue Service. 2025 Instructions for Form 2210 Without the attachment, IRS processing defaults to the equal-installment assumption and may assess a penalty automatically.
Situations Where This Method Is Not the Right Tool
Farmers and Fishermen
If at least two-thirds of your gross income comes from farming or fishing, you don’t need four quarterly payments. You can make a single estimated payment by January 15 of the following year, or skip estimated payments entirely by filing and paying the full balance by March 1.8Internal Revenue Service. Farming and Fishing Income Annualizing is rarely useful when this rule already applies.
Penalty Waivers
Separately from annualizing, the IRS can waive the underpayment penalty entirely if the shortfall came from a casualty, disaster, or other unusual circumstance where the penalty would be unfair. A separate waiver covers taxpayers who retired after reaching age 62 or became disabled in the tax year or the year before, if the underpayment was due to reasonable cause. Both waivers are requested on Form 2210.9Office of the Law Revision Counsel. 26 USC 6654 – Failure by Individual to Pay Estimated Income Tax
State Estimated Tax
State treatment varies. Most states with an income tax impose their own estimated payment rules and underpayment penalties. Some accept or mirror the federal annualized method; others use different periods, percentages, or interest rates. Using the federal method on your 1040 does not automatically cover your state return, so check your state’s rules before assuming both are protected.