The estimated tax safe harbor (Form 1040-ES, IRC 6654) is a cash-flow rule: pay at least 100% of last year's total tax (110% if prior-year AGI was over $150,000), minus expected federal withholding, then split the rest by 4. Hit that target and the underpayment penalty generally stays off, even if this year's tax is higher.
$10,000 prior-year tax, $6,000 expected withholding, AGI not over $150,000: $1,000 each quarter.
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This page does not compute 90% of current-year tax, the MFS $75,000 AGI threshold, or farmer/fisherman rules. It is not a Form 1040 engine. See estimated taxes and Publication 505. Estimate, not tax advice.
Direct answer: $10,000 → $1,000 / quarter
- Required annual = $10,000 × 100% = $10,000
- Still to pay via 1040-ES = $10,000 − $6,000 = $4,000
- Each quarter = $4,000 ÷ 4 = $1,000
If prior-year AGI was over $150,000: required $11,000, remaining $5,000, quarterly $1,250.
rate = 100% (or 110% if prior-year AGI > $150,000) required annual = prior-year total tax × rate remaining = max(0, required annual − expected withholding) quarterly = remaining / 4
Checks you can re-run
| Prior-year tax | Expected withholding | AGI over $150k | Required annual | Per quarter |
|---|---|---|---|---|
| $5,000 | $2,000 | No | $5,000 | $750 |
| $10,000 | $6,000 | No | $10,000 | $1,000 |
| $10,000 | $6,000 | Yes | $11,000 | $1,250 |
| $10,000 | $10,000 | No | $10,000 | $0 |
If withholding already covers the harbor, remaining and quarterly are $0. Extra W-2 withholding (W-4 Step 4(c)) can replace some or all of the 1040-ES checks. That is a timing choice, not a different tax.
Freelancers often start from self-employment take-home ($50,000 single → $39,539.11 in that model, quarterly slice $2,615.22). Whether that slice meets this harbor depends on last year's Form 1040 total tax, not on this year's SECA estimate.
What this is not
- Not 90% of this year's tax. Current-year income can be far from last year; the harbor still uses last year.
- Not backup withholding. A missing TIN on a 1099 is 24% at the source: backup withholding.
- Not Pub 15-T on a W-2. Employees who only have wage withholding use federal tax withholding and, if needed, W-4 Step 4.
Total tax, the figure the harbor statute uses, not AGI and not the refund. AGI only flips the 100% / 110% switch.
No. Last year's total tax already went through whatever deduction you took. This worksheet does not recompute a 2026 standard deduction.
Raise the withholding input. At $10,000 prior tax and $10,000 expected withholding, quarterly is $0.