How to Avoid Underpayment Penalty: Safe Harbor, W-4, and Waivers

To avoid an IRS underpayment penalty, pay in at least 90% of your current-year tax or 100% of last year’s tax (110% if last year’s adjusted gross income was over $150,000) through withholding and estimated payments. Hit either safe harbor and no penalty applies, no matter how much you still owe at filing. And if your remaining balance after withholding and refundable credits is under $1,000, the penalty doesn’t apply at all.¹

The federal system is pay-as-you-go: tax is owed as income is earned, not just in April.² Fall short during the year and the IRS charges interest on the shortfall at a rate that resets quarterly.

Pick a Safe Harbor Target

You only need to meet one of three thresholds to guarantee no penalty.¹

90% of the total tax on this year’s return.
100% of the total tax shown on last year’s Form 1040.
110% of last year’s tax if your prior-year adjusted gross income was over $150,000 ($75,000 if married filing separately).

For most people, the prior-year path is the easiest. Last year’s tax is a fixed number sitting on your return, so you know exactly what to aim for. Divide it into four, or set withholding to cover it, and you’re done. The 90% current-year path is more useful when your income is dropping sharply, because paying based on a much higher prior year would mean overpaying and waiting for a refund. Pick whichever produces the lower required payment.

A worked example for the higher-earner rule: if last year’s total tax was $20,000 and your prior-year AGI cleared $150,000, your 2026 safe harbor payment is $22,000, not $20,000.

Adjust Your W-4 to Hit the Number

If you have a paycheck, changing your W-4 is usually the cleanest route. File a revised Form W-4 with payroll and use line 4(c) to add a specific extra dollar amount per pay period.³ A $6,000 gap over 20 remaining pay periods is $300 per check.

Withholding has a timing advantage that estimated payments don’t. The tax code treats all withholding as if it were paid in four equal installments across the year, even when most of it came out of your last few paychecks.¹ Realize in October that you’re way behind? Crank up withholding for the rest of the year and the IRS credits that money as though it arrived evenly since January. Estimated payments get no such treatment; they count only on the date you send them.

The IRS Tax Withholding Estimator will do the math and produce a completed W-4 to hand to payroll.⁴

Make Quarterly Estimated Payments When Withholding Isn’t Enough

Freelance income, rental income, investment gains, and retirement distributions typically arrive without withholding. For those, the IRS expects estimated payments on four dates for calendar-year filers:⁵

April 15 (income from January through March)
June 15 (April and May)
September 15 (June through August)
January 15 of the following year (September through December)

All four 2026 deadlines fall on regular business days.⁶ Each installment is 25% of your required annual payment. So a $20,000 safe harbor target means roughly $5,000 by each deadline. Paying the whole amount in the fourth quarter won’t retroactively cover the earlier periods, and the IRS can charge a penalty for each period that came up short.

IRS Direct Pay moves money from a checking or savings account at no cost and credits the payment on the date you select.⁷ The Electronic Federal Tax Payment System (EFTPS) is another free option. Paper vouchers with Form 1040-ES still work but depend on the mail.

Cover a One-Time Income Spike

A home sale, exercised stock options, or a large bonus can blow past your normal withholding fast. Two practical fixes exist.⁸

The first is to increase the estimated payment for the quarter the windfall lands in. Sold an investment in August? Bump your September 15 payment to cover the capital gains tax. Publication 505 has a worksheet for estimating tax on capital gains and qualified dividends.

The second is to raise W-4 withholding for the rest of the year. Because withholding is treated as paid evenly, this can retroactively cover earlier quarters. That matters when a big event happened months before you noticed the tax consequences.

Use the Annualized Income Method for Uneven Earnings

Standard quarterly installments assume you earn evenly across the year. Seasonal businesses, commission-based work, and lumpy investment income don’t work that way. The annualized income installment method lets you base each quarter’s required payment on what you actually earned during that period rather than on a flat quarter of the yearly total.⁹

Schedule AI of Form 2210 breaks the year into four cumulative windows (January through March, January through May, January through August, and the full year). You compute income, deductions, and tax as if each window were the whole year, then annualize. If almost nothing came in during Q1 but Q4 was strong, this method sharply reduces the Q1 installment you needed to make. The cost is bookkeeping: you have to track income and deductions by month, and Schedule AI is one of the fiddlier IRS forms. Attach it to your return so the IRS sees why your payments matched your actual earning pattern.

Farmers and Fishermen: Different Rules

If at least two-thirds of your gross income comes from farming or fishing (measured against either the current or prior year), the quarterly system doesn’t apply.¹ You get a single estimated tax deadline: January 15 of the following year. And the required annual payment uses a lower 66⅔% current-year threshold instead of 90%.

There’s a simpler alternative. File the return and pay the full balance by March 1 of the following year and estimated payments can be skipped entirely.¹⁰

Ask for a Waiver If You Missed Anyway

The IRS can waive the underpayment penalty in two situations.¹¹

Casualty, disaster, or other unusual circumstance outside your control. Check Box A in Part II of Form 2210 and attach documentation such as police reports, insurance records, or a FEMA declaration.
Retirement after age 62 or disability during the tax year or the year before, where the underpayment resulted from that change rather than neglect. Check Box B on Form 2210 and include proof of retirement date and age, or of the disability.

Attach Form 2210 and a written explanation to the return. Each request is reviewed individually. One thing that trips people up: the First-Time Penalty Abatement program does not cover estimated tax underpayment penalties.¹² It applies to failure-to-file and failure-to-pay penalties under different code sections.

State Penalties Are Separate

Hitting the federal safe harbor does not shield you from state underpayment penalties. Most states with an income tax charge their own, and the rules vary. Some mirror the federal thresholds, others set different percentages or interest rates. Check your state department of revenue for its specific requirements; assuming federal compliance covers the state is a common and costly mistake.

1
Office of the Law Revision Counsel. 26 USC 6654 – Failure by Individual to Pay Estimated Income Tax
2
Internal Revenue Service. Pay As You Go, So You Won’t Owe: A Guide to Withholding, Estimated Taxes and Ways to Avoid the Estimated Tax Penalty
3
Internal Revenue Service. Form W-4 2026 Employee’s Withholding Certificate
4
Internal Revenue Service. Tax Withholding Estimator
5
Internal Revenue Service. Individuals 2
6
Internal Revenue Service. Publication 509 (2026), Tax Calendars
7
Internal Revenue Service. Direct Pay Help
8
Internal Revenue Service. Large Gains, Lump Sum Distributions, Etc.
9
Internal Revenue Service. Instructions for Form 2210 (2025)
10
Internal Revenue Service. Farmers and Fishermen
11
Internal Revenue Service. Instructions for Form 2210 (2025)
12
Internal Revenue Service. Administrative Penalty Relief