Form 2210 Worksheet: Schedule AI, Waivers, and Common Errors

The Form 2210 worksheet is how you calculate the penalty for underpaying your federal income tax during the year, and, more importantly, how you lower it. The IRS will compute a penalty for you if you leave the line blank on your Form 1040, but its default math assumes your income arrived in four equal pieces and that you owed the same installment in April as you did in September. Running the worksheet yourself is what lets you override that assumption, apply the annualized income method, or request a waiver.

Do You Need to Run the Worksheet at All?

Start with the threshold. If your total tax minus withholding and refundable credits is less than $1,000, there is no penalty and no worksheet.¹

Above that threshold, two safe harbors let you off. Your payments cover at least 90% of this year’s tax,² or they equal at least 100% of the tax on last year’s return (assuming it covered 12 months).³ Hitting either one is enough.

Higher earners face a tougher version. If your prior-year adjusted gross income exceeded $150,000 ($75,000 for married filing separately), the second safe harbor rises from 100% to 110%.³ The trigger looks at last year’s AGI, not this year’s.⁴ People whose income spiked this year sometimes assume they are stuck with the 110% test when they are not.

If you clear a safe harbor, you generally do not file Form 2210. You do have to file it in three situations: when you are using the Annualized Income Installment Method to lower the penalty, when you are asking for a waiver, or when you are reporting a figure smaller than the IRS would calculate on its own.¹

How the Standard Calculation Works

Part I of the worksheet starts with your required annual payment: the smaller of 90% of this year’s tax or 100% (or 110%) of last year’s.² The standard method then slices that figure into four equal installments of 25% each.³ The due dates are:⁵

April 15, for income from January 1 through March 31
June 15, for income from April 1 through May 31
September 15, for income from June 1 through August 31
January 15 of the following year, for income from September 1 through December 31

When a date lands on a weekend or federal holiday it shifts to the next business day. Withholding, unless you can show otherwise, gets spread equally across the four periods.

Part II then puts what you actually paid for each period next to what you owed. Any overpayment in one period carries forward and offsets a shortfall in the next. The penalty applies only to the net underpayment and only for the days between the installment due date and the date you either covered the gap or hit the return’s original due date, whichever came first. Skipping the carryover step is a common error that produces a penalty on money the IRS already held.

The Interest Rate the Worksheet Applies

The penalty is not a flat fee. It is interest on the underpayment, calculated using a rate the IRS resets quarterly: the federal short-term rate plus three percentage points.⁶

For 2026 the published individual underpayment rates so far are 7% per year for the first quarter⁷ and 6% per year for the second quarter,⁸ both compounded daily. Later quarters are posted on the IRS’s quarterly interest rates page as they are set.⁹

Because the rate can change each quarter, the worksheet applies a different daily factor to each installment period, which is why Part III asks for exact payment dates rather than lump-sum amounts. An April 15 underpayment accrues at whatever rate is in effect from April onward until you cover it.

Schedule AI: The Main Reason to File Form 2210 Yourself

The Annualized Income Installment Method is the single most effective lever on this form. If you earned most of your income in the second half of the year, the standard four-equal-installment method charges you for shortfalls on income you had not yet received. Schedule AI recalculates each installment based on what you actually earned through that point in the year.¹

It is built for freelancers with seasonal spikes, partners who get large year-end distributions, investors who realize capital gains late, and anyone whose income does not divide neatly into quarters.

The Four Periods and the Annualization Factors

Schedule AI asks you to calculate adjusted gross income for four cumulative periods, each starting January 1:¹

Period 1: January 1 through March 31
Period 2: January 1 through May 31
Period 3: January 1 through August 31
Period 4: the full year

For each window you report actual income, above-the-line deductions, itemized or standard deductions, and credits as they stood at the end date. Self-employed filers need net profit for each short period, not just the annual figure, so this works only if your bookkeeping is tied to dates.

Each period’s AGI then gets multiplied by an annualization factor to project a full-year equivalent:¹

Period 1: multiply by 4
Period 2: multiply by 2.4
Period 3: multiply by 1.5
Period 4: multiply by 1

Earn $30,000 in the first three months and the factor of 4 projects $120,000 for the year. Earn only $10,000 because the work had not picked up, and the projection drops to $40,000, with a correspondingly smaller required installment.

The Required Cumulative Percentages

Apply the regular tax rate schedules to each annualized figure to get an estimated full-year liability for that period. Schedule AI then uses escalating percentages to set the cumulative payment you should have made by each due date:

By April 15: 22.5% of the Period 1 annualized tax
By June 15: 45% of the Period 2 annualized tax
By September 15: 67.5% of the Period 3 annualized tax
By January 15: 90% of the Period 4 annualized tax

These line up with the 90% current-year safe harbor. The schedule compares your cumulative payments (withholding plus any estimated payments) against those required amounts and feeds the result into Part III, which recomputes the penalty using the AIIM figures rather than four equal quarters. For someone who earned 70% of the year’s income after Labor Day, the drop can be dramatic or complete.

You have to file the full Form 2210 with Schedule AI attached to get this treatment, even if the schedule produces a zero penalty. Without the paperwork, the IRS stays with its equal-installment default.¹⁰

Asking for a Waiver on the Form

Even when the math produces a penalty, two statutory waivers can erase it.³

The first covers casualty, disaster, or other unusual circumstances that would make the penalty unfair, such as a federally declared disaster that destroyed records or a serious illness during the year. You check Box A in Part II for a full waiver or Box B for a partial one, and you attach a written statement explaining the event and how it kept you from paying on time.¹ A Box A request only needs page 1 of the form; a Box B request requires you to calculate both the full penalty and the amount you want removed.

The second waiver is for people who retired after reaching age 62 or became disabled during the tax year in question or the one before it, provided the underpayment was due to reasonable cause and not willful neglect.³ Neither waiver is automatic. The IRS reviews your explanation before granting relief, and if a notice arrives after filing you can also call the number on it to request abatement at that point.

Attaching the Worksheet to Your Return

If you are content to let the IRS compute a standard penalty, you do not file the form at all. You file your return, and a separate bill arrives. If you used Schedule AI, requested a waiver, or arrived at a figure lower than the IRS’s default would produce, Form 2210 must go in with the return as the basis for your number.¹⁰

For paper filing, the form (with Schedule AI and any waiver statement) attaches to the back of your Form 1040, and the penalty amount goes on the estimated tax penalty line. For e-filing, most software handles Form 2210 once you flag uneven income or a waiver request. Make sure the penalty figure on Form 1040 matches the worksheet’s result; a mismatch triggers manual review and delays any refund.

Mistakes That Push the Worksheet Higher Than It Should Be

The costliest mistake is skipping Schedule AI when your income was uneven. The IRS will not annualize for you, so if you leave the standard method in place the penalty gets charged against installments on income you had not yet earned.

The second is confusing which year’s AGI triggers the 110% safe harbor. The $150,000 test looks at the prior year, not the current one. People whose income jumped this year sometimes overpay estimated taxes trying to clear a bar that does not apply to them yet.

The third is losing the carryover between periods. An overpayment in one quarter reduces an underpayment in the next, and the worksheet tracks this cumulatively. Work through each period in order before deciding whether you were short.

1
Internal Revenue Service. Form 2210 – Underpayment of Estimated Tax by Individuals, Estates, and Trusts
2
Internal Revenue Service. Topic No. 306 – Penalty for Underpayment of Estimated Tax
3
Office of the Law Revision Counsel. 26 USC 6654 – Failure by Individual To Pay Estimated Income Tax
4
Internal Revenue Service. Publication 505 – Tax Withholding and Estimated Tax
5
Internal Revenue Service. Frequently Asked Questions on Estimated Taxes for Individuals
6
Office of the Law Revision Counsel. 26 USC 6621 – Determination of Rate of Interest
7
Internal Revenue Service. Interest Rates Remain the Same for the First Quarter of 2026
8
Internal Revenue Service. Internal Revenue Bulletin 2026-08
9
Internal Revenue Service. Quarterly Interest Rates
10
Internal Revenue Service. Instructions for Form 2210