The Internal Revenue Service caps its failure-to-file penalty at five months, after which the charge for filing a return late stops growing no matter how much longer the return remains outstanding. A second, separate penalty for not paying the tax owed follows no such limit and keeps compounding until the balance is paid in full, according to IRS guidance updated this year. The distinction matters for taxpayers who requested a filing extension this spring and now face an October 15 deadline, because submitting the paperwork on time silences only one of the two penalty clocks running against an unpaid balance.
Two Separate Penalties Share One Monthly Meter
The failure-to-file penalty is calculated at 5% of the unpaid tax for each month or partial month a return is late, accumulating up to a maximum of 25% of the balance due. The failure-to-pay penalty runs on a separate track, charging 0.5% of the unpaid tax for each month or partial month the balance goes unpaid, with its own independent 25% ceiling. When both penalties apply to the same month, the IRS does not add the two rates together; it reduces the filing penalty by the amount the payment penalty already charged that month, so a return that is both late and unpaid faces roughly 4.5% for the filing penalty and 0.5% for the payment penalty in each of those overlapping months, rather than 5.5% combined.
A separate floor complicates the math for smaller balances. If a return arrives more than 60 days after its due date, the minimum failure-to-file penalty is set at $525 for returns due after December 31, 2025, or 100% of the unpaid tax, whichever is less, replacing the percentage calculation with a flat charge. A taxpayer who owes a modest amount and files six months late can therefore face a penalty set by that fixed dollar figure rather than by the 5%-per-month formula, since the minimum applies regardless of how small the underlying balance is.
Free refund decision tree: A delayed refund usually means one of a few specific things, and each has a different next step. Find the reason with the free refund tracker.
October 15 Marks the Filing Clock, Not the Payment Clock
The extension that pushes a filing deadline to October 15 addresses only the failure-to-file penalty, not the failure-to-pay penalty, a distinction the agency states plainly in its own instructions. Anyone requesting more time to file is told directly to pay any tax owed by the original April due date, since the extension covers the paperwork rather than the payment itself. A taxpayer who filed for the extension in April but never sent a payment has been accruing the failure-to-pay penalty since spring, regardless of whether the return is eventually filed on time by October 15.
That timing gap catches taxpayers who treat the extension as a pause on the entire tax obligation rather than a pause on the paperwork alone. A return filed on October 15 that still carries an unpaid balance will show a failure-to-pay penalty stretching back roughly six months, from the April due date through the October filing date, even though the failure-to-file penalty never applies at all because the return arrived by its extended deadline. The filing penalty in that scenario is zero; the payment penalty is not, and it has been compounding for the entire six months the extension was outstanding.
The failure-to-pay penalty is calculated only on the unpaid portion of the balance, not the entire tax liability, so a taxpayer who paid most of an estimated bill by April and covers the rest by October 15 owes the 0.5% monthly charge on just the remaining amount, not the full sum originally due. That detail rewards partial payment over doing nothing, since even an imperfect estimate sent by the spring deadline shrinks the base the penalty is calculated against for every month the extension runs.
Both penalty pages carry the same caveat about what rides alongside either charge: interest continues to accrue on top of whichever penalty applies, and by law the agency cannot waive that interest unless the underlying penalty itself is removed or reduced. A taxpayer disputing either penalty for reasonable cause is therefore disputing two things at once, the percentage-based charge and the interest accumulating on it, since resolving one without addressing the other leaves the balance still growing in the background.
What Continues After the Filing Penalty Stops
The IRS states the sequencing directly on its own penalty page: once a return passes five months late, the failure-to-file penalty has already reached its ceiling and stops adding to the balance, while the failure-to-pay penalty keeps accruing at 0.5% a month for as long as the tax goes unpaid. That second penalty carries its own 25% ceiling, separate from the filing penalty’s cap, so a taxpayer who lets both a return and a balance sit unresolved long enough can eventually face two penalties each maxed at a quarter of the unpaid tax, layered on top of each other rather than replacing one another.
The failure-to-pay rate is not fixed at 0.5% under every circumstance. A taxpayer who filed the return on time and later sets up an approved installment agreement sees the rate cut to 0.25% a month for the life of that plan, an incentive built into the penalty structure that rewards arranging payment terms before the agency has to pursue the balance. On the other end, a taxpayer who ignores a notice of intent to levy for ten days after it is issued sees the same penalty jump to 1% a month, a rate four times the ordinary charge that applies specifically to collection enforcement rather than routine late payment.
Neither rate change follows automatically of the October 15 deadline itself. Filing by that date closes out the failure-to-file penalty for anyone who requested an extension, but it does nothing to the failure-to-pay penalty already running on an unpaid balance, and nothing about that penalty’s separate 25% ceiling changes because the paperwork arrived on time. The dispute process the IRS outlines for either penalty treats them as separate line items precisely because one clock can stop while the other keeps running well past the date a return is finally filed.
Penalty Clocks That Keep Running After October
A penalty notice explaining an accruing failure-to-pay balance is only one of several notice types the IRS sends once a return has been processed, and the codes and deadlines printed on those notices rarely explain themselves. A taxpayer working through a penalty calculation on one piece of IRS mail often has a second, unrelated question sitting on a different notice, particularly when a return filed close to October 15 is also waiting on a refund tied to an earlier adjustment.
The IRS Refund Recovery Kit is a 13-page kit with a notice decoder and the refund-trace steps under Form 3911 for sorting out what a piece of IRS correspondence is actually asking for.
Look up the 3-year refund deadline and the refund status tracker in The IRS Refund Recovery Kit.
This article was researched and drafted with the assistance of AI and reviewed by The Money Overview editorial team.
