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Quarterly Safe-Harbor Payment Calculator

Size your estimated-tax payments to dodge the IRS underpayment penalty — the 90%/100%/110% safe-harbor rules, split into four quarters.

Prior-year total tax

Prior-year AGI

Expected current-year tax

Expected withholding this year

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How it works

Safe harbor = min( 90% of current-year tax , 100% of prior-year tax [110% if prior AGI > $150,000] ) · Quarterly = (safe harbor − withholding) ÷ 4

The IRS charges an underpayment penalty unless you prepay enough tax during the year. You are safe if your payments and withholding reach the smaller of 90% of this year’s tax or 100% of last year’s (110% when your prior-year AGI topped $150,000). Withholding counts toward the target no matter when it was taken, so you only need to make estimated payments for the shortfall, typically in four roughly equal installments.

Worked example

Last year you owed $20,000 on $130,000 AGI (so the 100% rule applies), and you expect $26,000 this year with $6,000 of withholding. The safe harbor is the lesser of 90% × 26,000 = $23,400 and 100% × 20,000 = $20,000, i.e. $20,000. After withholding, $14,000 over four quarters is about $3,500 each.

Frequently asked questions

How do I avoid the underpayment penalty?

Prepay, through withholding and estimated payments, at least the smaller of 90% of the current year’s tax or 100% of last year’s (110% if your prior-year AGI was over $150,000). Meeting either the current-year or prior-year figure is enough.

Does withholding count toward the safe harbor?

Yes, and it is treated as paid evenly across the year regardless of when it was actually withheld. That is why increasing W-2 withholding late in the year can cure an estimated-tax shortfall the quarterly payments would not.

When are the quarterly payments due?

Federal estimates are generally due April 15, June 15, September 15 and January 15 of the following year. The periods are uneven, but many people simply pay a quarter of the target on each date.

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Educational estimate using 2024 U.S. federal figures — ignores state tax, credits, phase-outs and your full situation. Not tax advice; confirm with a professional or the IRS.