Taxpayers who asked the IRS for more time to file their 2025 returns have until Oct. 15 to get those returns in. The extension does not cover the money, though, and any tax still unpaid since April has been accruing interest at 7% a year. The IRS set that rate for the quarter that began Oct. 1, and it matches the rate for the previous quarter, so the cost of owing has not gone up.
For retirees with a balance due, the practical effect is simple: each day the bill stays open adds a little more to it. The agency’s own pages spell out how the clock runs and what stops it.
The extension moves the filing date, not the payment date
The IRS describes the automatic extension as giving taxpayers until October 15 to file without penalties. The same page is blunt about the money side: filers should pay any tax owed by the April filing date, because the extension is only for filing the return. The agency’s filing-date guidance lists April 15, 2026, as the original due date for these returns, and that is the date from which the tax itself was due.
In practice, a return filed on Oct. 14 under an extension is on time, while a payment made on Oct. 14 is roughly six months late. The IRS says the extension request is made on Form 4868, which can be submitted online, by mail or through a tax professional. Filing the form after April does not reach back and move the payment date.
What 7% a year means on a balance still open
According to the IRS table of quarterly interest rates, the rate on individual underpayments for the quarter beginning Oct. 1, 2026, is 7%. The rate for the quarter beginning July 1 was also 7%. The agency attributes the figure to Internal Revenue Bulletin 2026-36 and says it is set at the federal short-term rate plus 3 percentage points.
Because the rate is unchanged, a taxpayer who owed in the summer is paying the same annual percentage this fall. The pressure comes from time, not from a new rate. The IRS states that interest accrues on unpaid tax, penalties and interest until the balance is paid in full, and that the rate is compounded daily. Interest on a balance of that kind also applies to any penalties added to it, so a penalty left open grows along with the original tax.
The agency’s interest page adds three points that matter to anyone planning around the Oct. 15 date. Interest on an underpayment starts on the due date of the amount owed and continues until the balance is paid. An installment agreement lets a taxpayer pay the remaining balance over time, but interest continues to accrue daily while payments are made. And the IRS says it does not remove or reduce interest for reasonable cause or as first-time relief. Interest can be reduced only where it results from an unreasonable error or delay by an IRS officer or employee, and a request for that goes on Form 843.
Ways to pay before the extended date
The IRS payments page lists the options for settling a balance. A bank-account payment through Direct Pay accepts all tax payments and is listed as free. Debit and credit card payments and digital wallet payments are accepted for most tax payments, with fees applying. A same-day wire is also listed, with fees that may apply, along with check or money order and cash. The same page points taxpayers who cannot pay in full to payment plans and installment agreements.
No amount is too small to matter for interest purposes, since the charge runs on whatever portion remains unpaid. A partial payment sent before Oct. 15 reduces the balance on which later interest is calculated, though the IRS pages read for this article do not set out how it applies payments between tax, penalties and interest.
What the IRS pages do not say
None of the IRS pages read for this article names an individual official responsible for the extension date or the rate, so the figures here rest on the Internal Revenue Service itself. The interest rate table is the agency’s published record for the quarter, and the extension page is its stated rule for filers.
The pages also do not state the amount of any failure-to-pay penalty, which is a separate charge from interest, so no penalty figure is given here. A balance’s total cost depends on the tax owed, how long it stays open and any penalties assessed.
The controlling facts are narrow and checkable. Oct. 15 is the extended filing date, the extension is for filing only, and the individual underpayment rate for the quarter beginning Oct. 1, 2026, is 7%, unchanged from the quarter before, according to the IRS tables dated September 2026.
Reading the IRS letters that follow an unpaid balance
The IRS Refund Recovery Kit is written for taxpayers who receive IRS letters or are waiting on a refund and are unsure what a given notice is asking for. It is a separate paid guide, not part of the IRS and not a way to pay or settle a balance.
The IRS Refund Recovery Kit is a 13-page kit that includes a notice decoder and a refund status tracker spreadsheet, so each letter and each pending refund can be sorted and followed in one place.
Open the notice decoder to sort out what an IRS letter is asking for →
This article was produced with AI assistance and checked against the primary sources linked above.
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.
