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Estimated tax safe harbor calculator

Uneven income from K-1s, rentals and a business makes estimated tax hard to pin down. The safe harbor rules give you a number you can pay with confidence: no underpayment penalty, whatever this year brings.

  • Runs in your browser; nothing is stored
  • Educational, not advice

Your figures

Sample household

Filled in with a sample household. Replace any figure with yours.

Last year’s return

The “total tax” line on Form 1040.

Moves the 110% threshold from $150,000 to $75,000 of AGI.
This year

From wages, bonuses and retirement distributions.

Leave blank to rely on last year’s tax.

Estimated tax safe harbor

Sample household
Each installment
$29,550
four equal payments
Estimates for the year
$118,200
after withholding
Safe harbor amount
$156,200
110% of last year’s tax
Prior-year rule
110%
AGI over $150,000

Pay $29,550 in each of four installments ($118,200 in all) and, with $38,000 of withholding, you’re inside the safe harbor based on 110% of last year’s tax.

  1. 1. Mid-April$29,550
  2. 2. Mid-June$29,550
  3. 3. Mid-September$29,550
  4. 4. Mid-January$29,550
Show the math
  1. Prior-year percentage110% if last year’s AGI was over $150,000, otherwise 100%110%
  2. Prior-year testLast year’s total tax × that percentage$156,200
  3. Current-year test90% of this year’s expected taxnot entered
  4. Safe harbor amountThe smaller test$156,200
  5. Estimated paymentsSafe harbor amount − withholding$118,200
  6. Each installmentEstimated payments ÷ 4$29,550
  • Installments are due mid-April, mid-June, mid-September and mid-January, moving to the next business day after a weekend or holiday.
  • The prior-year rule assumes last year was a full 12-month tax year and you filed a return.
  • Federal only. Your state may have its own estimated tax rules.
  • Educational, not tax advice. Your CPA can confirm your figures.

How this calculator works

You avoid the federal underpayment penalty if withholding and on-time estimated payments add up to the smaller of 90% of this year’s tax, or 100% of last year’s tax. If last year’s adjusted gross income was over $150,000 ($75,000 married filing separately), the prior-year figure is 110%.

The prior-year rule needs only last year’s return, so it’s the one you can rely on when this year is uncertain. If you also enter an estimate for this year, the calculator uses whichever test is smaller.

Payments are split into four equal installments, due in mid-April, mid-June, mid-September and mid-January (the next business day when the 15th falls on a weekend or holiday). This covers federal tax only; most states have their own rules.

Questions

Where do I find last year’s total tax and AGI?

On last year’s Form 1040: adjusted gross income is on the AGI line, and total tax is on the “total tax” line (not the balance due or refund).

Does withholding count differently from estimates?

Yes, in your favour: withholding is treated as paid evenly through the year, whenever it actually happens. Estimated payments count on the day they’re paid. This calculator assumes even installments.

My income is lumpy. Is there another option?

The annualized income installment method on Form 2210 can lower early payments when income arrives late in the year. Ask your CPA whether it fits.

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Educational, not advice. These tools use simplified models; take decisions to your CPA, attorney or adviser.