Line 8 of Form 2210 is your prior year’s total tax, and it sets a ceiling on how much you needed to prepay this year to avoid an underpayment penalty. You enter the prior year figure as-is if your prior year adjusted gross income was $150,000 or less ($75,000 or less if married filing separately), or you multiply it by 110% if your prior year AGI was higher.1Internal Revenue Service. Instructions for Form 2210 (2025)
How to Build the Number on Line 8
Start with the return you filed last year. Add your income tax and any additional taxes from Schedule 2 (self-employment tax, alternative minimum tax, and similar items). Then subtract refundable credits such as the earned income credit, additional child tax credit, and premium tax credit.1Internal Revenue Service. Instructions for Form 2210 (2025) The result is your prior year net tax liability. That figure is the raw material for Line 8.
Next, check your prior year AGI. If it was $150,000 or less (or $75,000 or less for married filing separately), enter the net tax liability directly.2Office of the Law Revision Counsel. 26 USC 6654 – Failure by Individual to Pay Estimated Income Tax If it exceeded that threshold, multiply the net tax by 110% and enter the higher figure. The AGI that governs this choice is from the prior year return, not the return you are filing now.
A Worked Example
Say your prior year tax was $30,000 and your prior year AGI was $140,000. You enter $30,000 on Line 8. Change one fact and push the prior year AGI to $165,000, and you multiply $30,000 by 110% and enter $33,000 instead. That $3,000 gap is the practical difference between the two safe harbors, and it matters most for taxpayers sitting near the threshold.
Why Line 8 Matters: The Smaller-of-Two Test
Form 2210 uses Line 8 as one half of a comparison. The other half is 90% of your current year’s tax. Your “required annual payment,” the amount you needed to cover through withholding and estimated payments to avoid a penalty, is the smaller of the two.2Office of the Law Revision Counsel. 26 USC 6654 – Failure by Individual to Pay Estimated Income Tax
Continuing the earlier example: if your prior year AGI was $140,000, Line 8 is $30,000. Suppose 90% of your current year tax comes to $36,000. The required annual payment is $30,000, because Line 8 is lower. If you paid at least that much through withholding and estimated tax, no penalty applies, even if your actual current year tax is $40,000.
That is what people mean by the prior year safe harbor. It lets you plan your payments off a number you already know, rather than a current year figure you might not be able to predict.
Filing Status Changed Between Years
A change in filing status complicates Line 8, because the number you need is the prior year’s tax for the people on this year’s return.
If you are filing jointly this year but filed separately last year, add your prior year tax to your spouse’s prior year tax and use the combined figure.1Internal Revenue Service. Instructions for Form 2210 (2025) If you are filing separately this year but filed jointly last year, you will need to allocate last year’s joint tax between the two spouses. The AGI test still keys off the prior year figures on the return you actually filed.
When Line 8 Doesn’t Apply
The prior year safe harbor is not always available. Two situations remove it entirely, and one removes the penalty altogether so Line 8 is moot.
Short prior-year return. Line 8 is only available if you filed a return for the prior year and that return covered a full 12-month period.3Office of the Law Revision Counsel. 26 U.S. Code 6654 – Failure by Individual to Pay Estimated Income Tax If you filed a short-year return, for example because you changed your accounting period, Line 8 is off the table and you are left with only the 90% current year test.
No prior year return, or first year as a U.S. taxpayer. If you did not file a prior year return, or if you moved to the U.S. mid-year and had no prior year U.S. return, you cannot use Line 8 either. The rule that lets you skip the penalty when you had zero prior year tax requires that the prior year was a full 12-month tax year and that you were a U.S. citizen or resident throughout it.2Office of the Law Revision Counsel. 26 USC 6654 – Failure by Individual to Pay Estimated Income Tax
Zero prior year tax liability. If your prior year tax was zero, and the year was a full 12-month tax year, and you were a U.S. citizen or resident throughout it, no penalty applies for the current year at all.2Office of the Law Revision Counsel. 26 USC 6654 – Failure by Individual to Pay Estimated Income Tax This frequently applies to people who had no income last year or whose deductions eliminated their tax. There is nothing to put on Line 8 because there is no Form 2210 to file.
Farmers and Fishermen Use a Different Form
If at least two-thirds of your gross income for the current or prior year comes from farming or fishing, you use Form 2210-F rather than Form 2210, and the safe harbor structure is more lenient. The required annual payment is the smaller of two-thirds of the current year’s tax or 100% of the prior year’s tax, and you can skip estimated payments entirely by filing and paying all tax due by March 1 of the following year.4Internal Revenue Service. Instructions for Form 2210-F (2025)
Once Line 8 Is Set
The rest of Form 2210 compares Line 8 against 90% of your current year’s tax, uses the lower amount as your required annual payment, and then measures your withholding and estimated payments against that figure. If you covered it, you owe no penalty regardless of how much tax you actually owe on your current return. If you didn’t, the later lines of the form calculate the shortfall and the resulting penalty.