The clock on this year’s tax-filing extensions runs out October 15, and the penalty for missing that date is steep from the first month: 5% of whatever tax remains unpaid, charged again for each month or partial month the return stays unfiled. For a retiree who requested an extension because of a complicated year — a home sale, an inherited IRA distribution, or paperwork that trickled in late from a brokerage — the deadline is the last checkpoint before that penalty clock starts running. Filing late costs far more than paying late, and the two penalties stack in ways that catch people off guard.
The Penalty That Starts at 5% and Can Reach 25%
The failure-to-file penalty is calculated as 5% of the tax still owed, minus any tax already paid on time or credits already applied, multiplied by the number of months or partial months the return is late. That 5% keeps compounding each month up to a maximum of 25% of the unpaid balance. If a return is more than 60 days late, a separate minimum penalty applies: for returns due after December 31, 2025, that minimum is $525 or 100% of the unpaid tax, whichever is smaller — meaning even a small balance can trigger a penalty far larger than the tax itself once two months have passed.
When a failure-to-file penalty and a failure-to-pay penalty both apply in the same month, the IRS reduces the combined rate to 5% total (4.5% for filing, 0.5% for paying) rather than stacking both in full, but the failure-to-file share still dominates the bill, according to the IRS’s failure-to-file penalty page.
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Interest Keeps Compounding Even If the Penalty Maxes Out
Penalties aren’t the only cost of an unpaid balance. The IRS announced that its interest rate for individual overpayments and underpayments will hold at 7% per year, compounded daily, for the quarter that began October 1, 2026, according to the agency’s fourth-quarter rate announcement. That rate is unchanged from the prior quarter and applies whether or not a failure-to-file penalty is also running. Unlike the failure-to-file penalty, interest has no 25% ceiling — it keeps accruing daily on whatever combination of tax and penalties remains unpaid until the balance is settled in full, which is part of why a bill that looks manageable in October can grow substantially by the time it’s finally paid off months later.
Free File Stays Open Through the Deadline
Taxpayers who requested an extension still have access to IRS Free File through October 15, 2026, which offers guided tax-preparation software at no cost to anyone with a 2025 adjusted gross income of $89,000 or less, along with built-in error checks that can catch mistakes before a return is submitted. Taxpayers above that income threshold can still use Free File Fillable Forms if they’re comfortable preparing their own return without guided software. Filing electronically and choosing direct deposit is also the fastest way to receive a refund for anyone who overpaid during the year, rather than waiting on a mailed check.
An Extension Bought Time to File, Not Time to Pay
The IRS’s own reminder to extension filers, issued August 26, 2026, put the distinction plainly: an extension gives more time to file a return, not more time to pay what’s owed, according to the agency’s extension-filer notice. That distinction is exactly why the failure-to-file penalty is ten times steeper per month than the failure-to-pay penalty alone — the IRS wants a return on file even when the taxpayer can’t cover the full balance yet. A taxpayer who can’t pay in full by October 15 is still better off filing on time and arranging a payment plan afterward than skipping the filing deadline altogether, since the failure-to-file penalty starts accruing the moment the extension deadline passes, regardless of whether any payment follows. A payment plan doesn’t erase the failure-to-pay penalty or the daily interest, but it stops the far steeper failure-to-file penalty from ever starting, since the return itself is on time even if the balance isn’t settled yet. For someone juggling a fixed retirement income against an unexpected tax bill, that difference between the two penalty tracks is often the single most consequential decision available before October 15.
Taxpayers who miss the deadline for a genuine reason beyond their control — a serious illness, a natural disaster, or another circumstance the IRS recognizes as reasonable cause — can request penalty relief rather than simply accepting the charge. That relief has to be requested and isn’t automatic, and it applies to the penalty itself rather than the interest that continues accruing on any unpaid tax underneath it. Reasonable-cause requests are made directly to the IRS, either in response to a notice already received or by writing in proactively, and are evaluated case by case rather than granted automatically on request.
Inside the kit
A notice decoder, the refund-trace steps for Form 3911, a refund status tracker spreadsheet and the 3-year refund deadline.
The IRS Refund Recovery Kit includes a 13-page kit, a notice decoder and the refund-trace steps (Form 3911).
Open The IRS Refund Recovery Kit.
This article was produced with the assistance of AI and reviewed by The Financial Wire editorial team.
Warren Cohen is a finance writer based in Phoenix, Arizona, covering personal finance topics including credit, banking, and beginner investing. He earned his degree in business administration from Arizona State University and began his career working in consumer finance, where he gained direct experience with lending and credit systems. He now writes for personal finance websites and fintech platforms, focusing on clear, practical content that helps readers make informed financial decisions.
