Payroll & contractors
Estimated Tax Safe Harbor Calculator
Work out the quarterly payment that avoids an underpayment penalty, including the 110% rule and the halved AGI threshold for married filing separately.
| Prior-year route110% of last year’s tax · high-AGI rate applies | $30,800 |
|---|---|
| Current-year route90% of this year’s expected tax | $30,600 |
| Lower of the twocurrent year | $30,600 |
| Less expected withholding | −$6,000 |
| Estimated payments needed | $24,600 |
| Q1April 15 | $6,150 |
|---|---|
| Q2June 15 | $6,150 |
| Q3September 15 | $6,150 |
| Q4January 15 (following year) | $6,150 |
Withholding counts toward the safe harbor and is treated as paid evenly across the year no matter when it happened. Raising withholding in December can therefore cure an earlier shortfall in a way that a Q4 estimated payment cannot.
Details people get wrong
- What is the safe harbor?
- Pay at least 90% of this year’s tax, or 100% of last year’s, and no underpayment penalty applies even if you end up owing more. The prior-year route is the useful one because you already know the number — this year’s tax is a guess until December.
- When does the 110% rule apply?
- If your prior-year adjusted gross income exceeded $150,000, the prior-year safe harbor rises from 100% to 110%. A good year quietly raises the bar for the following year, which is how people who did nothing wrong get penalised.
- Is the threshold different if married filing separately?
- Yes, and this is routinely missed. For married filing separately the AGI threshold is $75,000, not $150,000. Filing separately can push you into the 110% bracket at half the income, and most calculators do not ask about filing status at all.
- 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 makes withholding a useful late-year fix: increasing it in December can cure an underpayment from earlier quarters in a way that a Q4 estimated payment cannot.