Estimated Tax Safe Harbor Calculator (2026): Minimum Payments to Avoid the IRS Penalty
Find the minimum 2026 estimated tax that avoids the IRS underpayment penalty: the smaller of 90% of this year’s tax or 100% of last year’s (110% above $150,000 AGI, $75,000 married filing separately), minus withholding, split into the four 2026 due dates, with the $1,000 rule, the farmer and fisherman 66⅔% rule and last year’s refund applied.
How it works
Required annual payment = min(90% × 2026 tax, 100% × 2025 tax) · 110% replaces 100% if 2025 AGI > $150,000 ($75,000 married filing separately) · Farmers and fishermen: 66⅔% replaces 90%, no 110% rule · Estimated payments = required − withholding · Each installment = ¼ of that, due April 15, June 15, September 15 2026 and January 15 2027 · No penalty if 2026 tax − withholding < $1,000
The IRS charges an underpayment penalty when too little tax is paid during the year through withholding and estimated payments. You avoid it by paying at least the "required annual payment", which is the smaller of two safe harbors: 90% of your 2026 tax, or 100% of the tax on your 2025 return. If your 2025 adjusted gross income was over $150,000 (over $75,000 if you are married filing separately for 2026), the prior-year figure becomes 110%. The prior-year rule needs a 2025 return that covered a full 12 months; without one, only the 90% rule is available. Withholding counts first, and the rest is due in four equal installments on April 15, June 15 and September 15, 2026, and January 15, 2027. Withholding is treated as paid evenly through the year, while estimated payments count only on the date you make them. If you expect to owe less than $1,000 after withholding, no estimated payments are required. Farmers and fishermen who get at least two-thirds of their gross income from farming or fishing use 66⅔% instead of 90%, are not subject to the 110% rule, and can make a single payment by January 15, 2027 or file and pay everything by March 1, 2027. A 2025 refund you applied to 2026 counts as an estimated payment and covers the earliest installments. Meeting a safe harbor removes the penalty, not the tax: any remaining balance is still due when you file. "Total tax" here means Form 1040 line 24 (income tax plus self-employment and other taxes) minus refundable credits. State estimated taxes have separate rules.
Worked example
You expect $20,000 of total tax for 2026, owed $16,000 for 2025 with a 2025 AGI of $120,000, and will have $4,000 withheld. The current-year rule is 90% × $20,000 = $18,000. Your AGI is not over $150,000, so the prior-year rule is 100% × $16,000 = $16,000. The required annual payment is the smaller, $16,000. After $4,000 of withholding, $12,000 must come from estimated payments: $3,000 each on April 15, June 15 and September 15, 2026 and January 15, 2027. That avoids the penalty, but $20,000 − $4,000 − $12,000 = $4,000 will still be due when you file.
Sources: IRS Form 1040-ES (2026), Estimated Tax for Individuals · IRS Instructions for Form 2210 (2025), Underpayment of Estimated Tax · 26 U.S. Code § 6654, Failure by individual to pay estimated income tax (Cornell LII) · Keeper: The safe harbor rule for estimated taxes
Frequently asked questions
What are the 2026 estimated tax due dates?
For calendar-year filers: April 15, June 15 and September 15, 2026, and January 15, 2027. You can skip the January payment if you file your 2026 return by February 1, 2027 and pay the full balance with it.
When does the 110% rule apply?
When the AGI on your prior-year return was more than $150,000, or more than $75,000 if you are married filing separately for the current year. Then you must pay 110% of last year’s tax, not 100%, to use the prior-year safe harbor. It does not apply to qualifying farmers and fishermen.
Do I need to pay estimated tax if I owe less than $1,000?
No. If your total tax minus withholding (and refundable credits) is under $1,000, there is no underpayment penalty, so estimated payments are not required.
Which safe harbor should I use?
The prior-year rule is certain because last year’s tax is already known, so it suits rising or unpredictable income. The 90% rule can mean smaller payments if this year’s income is falling, but it relies on your projection being right.
Does withholding count differently from estimated payments?
Yes. Withholding is treated as paid evenly over the year no matter when it happened, so raising your withholding late in the year can cover earlier shortfalls. Estimated payments count on the date they are paid.
How is the underpayment penalty calculated?
It works like interest on each late or short installment, at the federal short-term rate plus 3 percentage points, from the due date until paid. Form 2210 instructions for 2025 use 7% a year. Meeting the smaller safe harbor on time avoids it entirely.
Do I still owe tax if I meet the safe harbor?
Yes. The safe harbor only removes the penalty. If your actual 2026 tax is higher than what you paid, you pay the difference by April 15, 2027 without a penalty.
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Educational estimate using US federal rules for tax year 2026. It does not compute your tax, state estimated taxes or the annualized method. Not tax advice; confirm with IRS guidance or a tax professional.