Schedule AI on Form 2210 lets you recalculate each estimated tax installment based on when you actually earned your income during the year, instead of assuming it arrived in four equal quarters. If a bonus, capital gain, or seasonal spike loaded most of your income into the back half of the year, the standard method treats you as though you underpaid the early quarters and charges a penalty for it. Schedule AI matches each required payment to what you actually owed by that point.
Who Schedule AI Is Built For
The 25%-per-quarter default punishes people whose income is lumpy. If you earned $20,000 through June and then received a $180,000 bonus in November, the standard method treats you as though you earned $50,000 in each quarter and penalizes you for underpaying the first two installments. That penalty is real money, and it’s avoidable.
The annualized method fits a handful of common situations: year-end bonuses or commissions, capital gains from a late-year stock sale, seasonal businesses with a concentrated earning window, and newly self-employed people whose income ramps up as the year progresses. The common thread is that income in the earlier months was genuinely lower than the standard method assumed. As the IRS frames it, a taxpayer shouldn’t owe a penalty for failing to pay tax on income that didn’t exist yet.1Internal Revenue Service. Underpayment of Estimated Tax by Individuals Penalty – Section: Annualized Income
The Four Annualization Periods
Schedule AI divides the year into four cumulative periods. Each period starts on January 1 and ends on a specific cutoff date. They are not separate quarters; each one includes all income from the start of the year through its endpoint:2Internal Revenue Service. Instructions for Form 2210 (2025)
- Period (a): January 1 through March 31 (payment due April 15)
- Period (b): January 1 through May 31 (payment due June 15)
- Period (c): January 1 through August 31 (payment due September 15)
- Period (d): January 1 through December 31 (payment due January 15 of the following year)
The cumulative structure matters. When you calculate period (c), you include all income from January through August, not just June through August. You need records showing exactly when each piece of income arrived and when each deductible expense was incurred. Allocating a December capital gain to period (a) would be wrong and could trigger trouble if examined.
How the Calculation Works
Once you know the taxable income for each cumulative period, you project it forward to estimate what a full year at that pace would look like. The IRS assigns a multiplier to each period:
- Period (a), 3 months of data: multiply by 4
- Period (b), 5 months of data: multiply by 2.4
- Period (c), 8 months of data: multiply by 1.5
- Period (d), 12 months of data: multiply by 1 (already a full year)
The result is your annualized taxable income for that installment. You calculate the tax on that figure using the standard rates and brackets for your filing status, subtract applicable credits, and apply a cumulative percentage to determine how much should have been paid by that date:3Internal Revenue Service. Form 2210 – Underpayment of Estimated Tax by Individuals, Estates, and Trusts
- Period (a): 22.5% of the annualized tax
- Period (b): 45% of the annualized tax, minus the period (a) required installment
- Period (c): 67.5% of the annualized tax, minus prior required installments
- Period (d): 90% of the annualized tax, minus prior required installments
Those percentages come from applying the 90% current-year safe harbor cumulatively across four installments (90% รท 4 = 22.5% per period, building to 90% by the fourth).
The Comparison That Reduces Your Penalty
For each period, you compare two numbers: the required installment under the standard 25% method and the required installment under the annualized method. You owe the smaller of the two.4Internal Revenue Service. Instructions for Form 2210 (2025) If your annualized calculation shows you owed very little through March because your income hadn’t arrived yet, the annualized installment for period (a) drops well below the standard one, and the lower number is what counts.
The Recapture Rule
Here’s the catch. If the annualized method reduces your required installment in an earlier period, the savings don’t disappear. The IRS adds the reduction back to the next period’s installment under the standard method.5Office of the Law Revision Counsel. 26 U.S. Code 6654 – Failure by Individual to Pay Estimated Income Tax If the annualized method saved you $3,000 in period (a), the standard installment for period (b) goes up by $3,000. The method shifts when you’re required to pay so it matches when you earned. It doesn’t reduce the total amount you owe for the year.
Allocating Withholding to When It Actually Happened
When Form 2210 tests whether your payments met each period’s required installment, paycheck withholding counts as a payment. The default rule spreads your total annual withholding evenly, treating one-fourth as paid on each installment due date.2Internal Revenue Service. Instructions for Form 2210 (2025)
That default can work against you if most of your withholding happened late in the year, for instance because of supplemental withholding on a December bonus. In that scenario, you may benefit from allocating withholding to the dates it was actually withheld instead. To do this, check box D in Part II of Form 2210 and attach the completed form to your return. You’ll need documentation of the actual withholding dates, typically your pay stubs. Combined with Schedule AI, this can further reduce or eliminate the penalty for earlier periods when both your income and your withholding were low.
If You’re Self-Employed
Self-employment adds a layer. Part II of Schedule AI is devoted to calculating your annualized self-employment tax for each period.4Internal Revenue Service. Instructions for Form 2210 (2025) You figure net earnings from self-employment for each cumulative period by multiplying your net profit through that date by 92.35%.
On line 1 of Part I, you must include the deductible half of self-employment tax as an adjustment. This is easy to overlook because the deduction itself depends on income that changes with each period, creating a circular calculation that takes care to get right. If your net self-employment earnings for a period fall below $400, you can skip Part II for that period since no self-employment tax would be due.
Married couples filing jointly where both spouses have self-employment income need to complete separate Part II worksheets and combine the results on line 15 of Part I.
Filing Schedule AI With Your Return
One rule catches many filers off guard: if you use the annualized method for any installment period, you must use it for all four.2Internal Revenue Service. Instructions for Form 2210 (2025) You can’t cherry-pick the annualized calculation for the two periods where it helps and use the standard method for the other two. The comparison between annualized and standard installments happens within Schedule AI for every period, and the form handles the selection automatically.
The practical sequence:
- Complete Part I of Form 2210 to confirm you owe a penalty at all (the $1,000 threshold and safe harbor checks).
- Check box C in Part II to indicate you’re using the annualized income installment method.
- Fill out Schedule AI with your income, deductions, and tax for each cumulative period. The schedule calculates the annualized installments.
- Complete Part III, Section A of Form 2210, transferring the required installment amounts from Schedule AI.
- Attach the completed Form 2210 and Schedule AI to your Form 1040 when you file.
Failing to attach Schedule AI means the IRS will ignore your annualized calculations and default to the standard 25%-per-quarter method. The penalty relief vanishes. Double-check that the schedule is included before you file.
A Note on Other Relief
Schedule AI is one route to a smaller penalty. Separate waivers exist for casualty and disaster situations (box A) and for taxpayers who retired after age 62 or became disabled (box B), each with its own documentation requirements.6Internal Revenue Service. Instructions for Form 2210 (2025)
Finally, the federal calculation doesn’t cover your state. Most states with an income tax impose their own estimated payment rules, some offer an annualized method and some don’t, and thresholds and interest rates vary. A strategy that eliminates your federal penalty can still leave a state bill behind, so check your state department of revenue for the equivalent form.