Thursday, October 15, 2026, is the extended deadline for 2025 federal income tax returns, and a return that misses it starts collecting a penalty of 5 percent of the unpaid tax for every month or part of a month it is late. The charge stops growing at 25 percent. The IRS also sets a minimum: for returns due after December 31, 2025, a return more than 60 days late owes $525 or the entire tax due, whichever is less.
5 percent a month, with a partial month counted as a whole one
The Internal Revenue Service’s failure-to-file penalty page, last updated February 7, 2026, states the rule in one sentence: the penalty is “5% of the tax due (less any tax paid on time and available credits) for each month or partial month the return is late,” and it “accrues up to a maximum of 25%.” The base is the balance still owed, not the whole year’s tax. A filer whose withholding and estimated payments covered most of the bill is charged on what remains after those payments and credits.
The words “partial month” carry most of the weight. A return filed one day past the deadline has been late for part of a month, and the page’s wording counts that as a full month. Five months of lateness reaches the 25 percent ceiling, so the penalty is front-loaded: the first month costs as much as any other, and a filer who is a week late pays the same 5 percent as one who is four weeks late.
Where failure-to-pay overlaps: 4.5 percent plus 0.5 percent
Two different penalties can run at once, and the IRS does not stack them. When both apply, according to the same page, “the failure to file penalty is reduced by the amount of the failure to pay penalty (0.5% for each month).” In a month when both are charged, the failure-to-file penalty is therefore 4.5 percent, the failure-to-pay penalty is 0.5 percent, and the combined charge is the familiar 5 percent. That is simple subtraction from the IRS’s own two figures.
The IRS adds that “after 5 months the failure to file penalty will max out, but the failure to pay penalty continues.” Five months at 4.5 percent comes to 22.5 percent, and the 0.5 percent failure-to-pay charge over the same five months adds 2.5 percent, which is how the combined figure reaches 25 percent. After that point only the failure-to-pay penalty keeps running on any tax still unpaid, so the cost of filing late is front-loaded while the cost of paying late is open-ended.
An extension moves the filing date, not the payment date
The IRS’s page on getting an extension to file, last reviewed September 20, 2026, says plainly that “the extension is only for filing your return.” Tax owed was still due by the original April deadline. A filer who requested an extension and did not pay by April has had the failure-to-pay penalty running since then, even though no failure-to-file penalty can start until the extended date passes.
The same page lists three free ways to request the extension: checking the extension box when paying online, which produces a confirmation number; using IRS Free File, which has no income limit for extensions; and filing Form 4868, the Application for Automatic Extension of Time To File U.S. Individual Income Tax Return, by mail, through an IRS partner, or through a tax professional. U.S. citizens and resident aliens living outside the country may receive an automatic two-month extension, and people affected by declared disasters may have more time to file than October 15.
The $525 minimum, and the table that ignores the extension
The failure-to-file page says the penalty applies “if you don’t file your tax return by the due date (including extensions).” Its minimum-penalty table, though, is organized by “Return Due Date (without extension).” For a 2025 return, the unextended due date was April 15, 2026, so the return falls in the row for returns due after December 31, 2025, where the minimum is $525.00. The row for returns due during 2025, which covered 2024 returns, shows $510.00, and earlier rows show $485.00 for returns due in 2024 and $450.00 for those due in 2023.
The reading error is easy to make: a filer who extended to October 15 might look up October’s date and conclude that the table’s top row does not apply, or might reach for the $510 figure that was current a year ago. The table keys on the unextended date, and the 2025 return belongs in the $525 row. The page’s minimum-penalty rule reads: “If the return is more than 60 days late, the minimum penalty is the amount listed below or 100% of the underpayment, whichever is less.” A small balance due therefore cannot generate a $525 charge, because the cap is the underpayment itself.
Reasonable cause and the one remedy the IRS names
The IRS says it “may be able to remove or reduce some penalties if you acted in good faith and can show reasonable cause for why you weren’t able to meet your tax obligations.” The page does not promise relief and sets no list of qualifying reasons, so the remedy is a request the IRS evaluates, not an automatic reduction.
The numbers that govern the outcome are all on the IRS penalty page: 5 percent a month, 4.5 percent when failure-to-pay overlaps, a 25 percent ceiling, and a $525 floor measured against the unextended due date.
Late filers and unclaimed refunds run on different clocks
The failure-to-file penalty is charged on tax that is owed, but some late filers are owed a refund instead, and a refund claim has a time limit of its own that is separate from the October 15 extension date. Returns that never got filed are where the two clocks collide.
The IRS Refund Recovery Kit includes the 3-year refund deadline and a refund status tracker spreadsheet for following a late-filed return through the IRS process.
See the 3-year refund deadline and status tracker →
This piece was drafted with AI assistance; the penalty rates, minimums and dates were checked against the IRS failure-to-file and extension pages cited above.
