The Extended Filing Deadline Falls on October 15. The Penalty for Missing It Is Ten Times the Penalty for Not Paying.

Taxpayers who filed Form 4868 in April bought six more months to file. That period ends in the middle of this month. What the extension did not buy was more time to pay, and the arithmetic of the two penalties explains why the filing deadline is the one worth protecting.

Two separate clocks

The IRS says, in terms, that an extension of time to file is not an extension of time to pay, and that taxes owed should be paid by the original due date to avoid possible penalties. Form 4868 must be filed by the original due date of the return. For calendar-year filers that date was April 15, 2026; the automatic extension runs six months from it.

The failure-to-file penalty

• 5% of the tax due for each month or part of a month the return is late, less any tax paid on time and available credits.
• Capped at 25% of the tax due, which is reached after five months.
• If a return is more than 60 days late, the minimum penalty is the smaller of the amount in the IRS penalty table or 100% of the underpayment. For 2025 returns the IRS lists that minimum as $510.

The failure-to-pay penalty

• 0.5% of the unpaid tax for each month or part of a month it remains unpaid, capped at 25% of the unpaid tax.
• 0.25% a month while an approved payment plan is in force.
• 1% a month or part month if the tax is still unpaid 10 days after a notice of intent to levy.
• Interest is charged separately from the penalties, and the IRS charges interest on penalties as well.

How the two interact

When both penalties apply in the same month, the failure-to-file penalty is reduced by the failure-to-pay penalty, so the combined charge is 5% a month rather than 5.5%. After five months the failure-to-file penalty reaches its 25% ceiling and stops. The failure-to-pay penalty keeps accruing after that, up to its own 25% ceiling. The practical consequence is structural rather than a matter of judgement: a return filed on time with the money still owed accrues at a tenth of the rate of a return that is simply not filed.

This article summarises published IRS guidance and is for informational purposes only. It is not tax or legal advice. Penalty and relief rules depend on individual facts; consult the IRS pages cited or a qualified tax professional about your own return.