Underpayment of Estimated Tax Penalty

Full Definition

The IRS frames the rule this penalty enforces in four words: "Taxes are pay-as-you-go." It states you need to pay most of your tax during the year as you receive income, rather than at the end of it, and that the penalty applies to individuals, estates and trusts that do not pay enough estimated tax on their income, or pay it late.

There are two ways to pay during the year: withholding from pay, pension or certain government payments such as Social Security; or quarterly estimated payments. The IRS publishes the quarterly due dates as April 15 for income earned January 1 to March 31, June 15 for April 1 to May 31, September 15 for June 1 to August 31, and January 15 of the following year for September 1 to December 31.

The IRS states it calculates the penalty on the tax shown on your original return, or a more recent return filed on or before the due date, and that the tax shown is total tax minus total refundable credits. The calculation turns on the amount of the underpayment, the period it was due and underpaid, and the published quarterly interest rates for underpayments.

Two exclusions make this penalty different from the others on this site, and both are the IRS's own words elsewhere. On reasonable cause: "Reasonable cause doesn't apply to certain penalties such as the estimated tax penalty." And on administrative relief: the compliance test for First Time Abate asks whether a penalty was assessed in the prior three years, "except the estimated tax penalty" — the estimated tax penalty does not spoil the record, and it is not one of the penalties the relief removes.

Sources

• Underpayment of Estimated Tax by Individuals Penalty — Internal Revenue Service, retrieved 2026-08-21
• Penalty relief for reasonable cause — Internal Revenue Service, retrieved 2026-08-20

Last reviewed 2026-08-21 by Tax Resolution Clarity editorial.