2026 tax year · Form 2210
Estimated tax penalty calculator
Miss a quarterly payment and the IRS charges interest on the shortfall, separately for each quarter. See what you owe, and whether the safe harbor saves you.
The US tax system is pay-as-you-go: you owe tax as you earn, through withholding or four quarterly estimated payments. Fall short and Form 2210 adds an underpayment penalty, really interest at the IRS rate, on whatever each quarter was under. The escape hatch is the safe harbor: pay enough and the penalty is zero no matter what you finally owe.
The prior-year safe harbor.
Over $150k raises the prior-year test to 110%.
Treated as paid evenly across the year.
Published quarterly by the IRS (short-term rate + 3%).
Enter your tax and what you paid to estimate the penalty.
The safe harbor is the whole game
You owe no penalty if your withholding plus estimated payments reach the lesser of two numbers: 90% of this year's tax, or 100% of last year's (110% if your prior-year AGI was over $150,000). Hit that line and it does not matter that you owe a big balance in April, the penalty is off.
Worked example
Someone with $20,000 of 2026 tax and $18,000 last year (AGI under $150,000) who made no estimated payments and had no withholding:
| Step | Amount |
|---|---|
| 90% of this year's tax | $18,000 |
| 100% of last year's tax | $18,000 |
| Safe-harbor target (the lesser) | $18,000 |
| Paid during the year | $0 |
| Estimated penalty at an 8% IRS rate | $900 |
Paying nothing against an $18,000 target runs a penalty of about $900 at an 8% IRS rate. Spreading four $4,500 payments across the year instead would have cleared the safe harbor and dropped the penalty to zero.
Questions
What is the IRS underpayment rate for 2026?
The rate is the federal short-term rate plus three percentage points, and the IRS republishes it every calendar quarter. So it is not a single fixed number for the year. Look up the current rate on the IRS "quarterly interest rates" page and enter it above; the calculator applies whatever rate you give it.
Does withholding count differently from estimated payments?
Yes, and in your favor. Withholding is treated as paid evenly across all four quarters no matter when it was actually withheld, so a big December withholding can still cover an early-year shortfall. Estimated payments only count for the quarter you actually made them.
Is this the exact Form 2210 figure?
It is a close estimate. This uses the short-cut method, each quarter needs a cumulative 25% of the required amount and the shortfall accrues for about a quarter. The real form uses exact dates and daily compounding, and the annualized-income method (Schedule AI) can lower the penalty if your income arrived unevenly during the year.
Can the penalty be waived?
Sometimes. The IRS can waive it for a casualty, disaster, or other unusual circumstance, or if you retired (after 62) or became disabled during the year and the underpayment was for reasonable cause.
Related tools
- Quarterly tax calculator what to pay so you never owe this penalty
- W-4 withholding calculator dial in withholding instead
- 1099 tax calculator total self-employment tax
Estimate for the 2026 tax year using the simplified Form 2210 method. The IRS underpayment rate is set quarterly, confirm the current figure. Not tax advice.