Quarterly Estimated Tax Safe Harbor Calculator

Identify the smallest IRS safe harbor target and convert it into quarterly payment instructions. Enter last year’s total tax, this year’s projected tax, and how many estimated payments remain so you can cover any shortfall before penalties apply.

Form 1040, line 24 from the prior year return.
Expected total tax for this year after deductions and credits.
How many quarterly vouchers are still due this year.
Optional. Combine W-2, 1099, and prior estimates paid so far.
Optional. Use 110 if prior-year AGI exceeded $150,000; blank keeps 100%.

For planning only — confirm thresholds with a tax professional before filing.

Examples

  • $18,750 prior-year tax, $22,400 projected this year, 3 payments left, $6,000 withheld, safe harbor 110% ⇒ Prior-year safe harbor (110.00% of last year): $20,625.00 • Current-year 90% threshold: $20,160.00 • Recommended safe harbor target: $20,160.00 (Current-year 90% threshold is the smaller target.) • Withholding counted so far: $6,000.00 • Amount still owed to hit safe harbor: $14,160.00 • Per-payment amount across 3.00 remaining estimate(s): $4,720.00
  • $12,400 prior-year tax, $9,800 projected this year, 2 payments left, withholding blank ⇒ Prior-year safe harbor (100.00% of last year): $12,400.00 • Current-year 90% threshold: $8,820.00 • Recommended safe harbor target: $8,820.00 (Current-year 90% threshold is the smaller target.) • Withholding counted so far: $0.00 • Amount still owed to hit safe harbor: $8,820.00 • Per-payment amount across 2.00 remaining estimate(s): $4,410.00

FAQ

Does this calculator handle state estimated tax rules?

It focuses on federal safe harbor thresholds. Many states mirror the 90%/100% framework, but check your state’s instructions before relying on the results.

What if my income swings wildly through the year?

Consider the annualized income installment method (Schedule AI) if early quarters were low. This safe harbor view assumes even income and payments.

Can payroll withholding at year-end replace quarterly vouchers?

Yes. Withholding is treated as if it were paid evenly throughout the year, so increasing W-2 or IRA withholding late in the year can still close a shortfall.

How do I account for self-employment tax?

Include self-employment tax inside the projected total tax field so your safe harbor covers both income and SE tax obligations.

Additional Information

  • Safe harbor rules let you avoid penalties by paying either 90% of the current-year tax or 100%/110% of last year’s liability, whichever is lower.
  • High earners (prior-year AGI above $150,000) generally must meet 110% of the prior-year tax to rely on that safe harbor.
  • Withholding counts evenly across quarters, so late-year payroll adjustments can close a gap even if earlier estimates were light.

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