Missed the October 15 Extension Deadline? What Happens Now, and What to Do

If you extended your 2025 return and didn't file by October 15, 2026, file as soon as you can, even if you can't pay the full balance. An extension gave you more time to file, not more time to pay. Any tax you didn't pay by April 15 has been building interest (7% a year for October through December 2026) and a late-payment penalty of 0.5% a month. Now that the extended deadline has passed, a much bigger late-filing penalty of up to 5% a month gets added too. If you're owed a refund, there's no late-filing penalty, but you still need to file to get the money.

What does a tax extension actually do?

An extension gives you about six more months to file your return. It doesn't give you more time to pay. For 2025 individual returns, filing Form 4868 (or making a payment and marking it as an extension payment) by April 15, 2026 moved the filing deadline to October 15, 2026. The tax itself was still due April 15.

That's why the IRS asks you to estimate what you owe when you extend. Whatever you didn't pay by April 15 started building interest and the late-payment penalty that day, extension or not.

Businesses have their own versions. S corporations and partnerships use Form 7004, and their extended deadline for calendar-year 2025 returns was September 15, 2026.

Is filing an extension a bad thing?

No. An extension is an automatic, routine request. The IRS doesn't ask for a reason, and a return filed by the extended deadline is on time.

CPAs extend returns all the time, usually for good reasons:

• Missing or corrected forms. K-1s from partnerships and S corporations, corrected 1099s from brokerages, and late statements often show up after April.
• Accuracy beats speed. A rushed return that has to be amended later costs more time and attention than one filed right the first time.
• Planning room. Some decisions can wait until the extended deadline. For example, a SEP-IRA can be opened and funded for a year as late as your filing deadline, including extensions. (More on that in my comparison of SEP-IRA vs. Solo 401(k).)

The problem isn't the extension. The problem is treating it as extra time to pay, or forgetting the October deadline.

How I handle extensions for my clients

When I extend a return for a client, I treat the extension as a payment deadline, not just a filing step. The goal is a reasonable estimate of the balance due by April 15 so that as much as possible gets paid on time. Then we work toward a complete return well before October 15, so the extended deadline is a backstop instead of a target. I'll also note anything we're waiting on, like K-1s or corrected forms, and keep the state return on the same track as the federal one.

What happens if you missed October 15?

If your extension ran out and you haven't filed, two penalties and interest can apply to any unpaid tax.

The failure-to-file penalty

• 5% of the unpaid tax for each month or part of a month the return is late, counted from the extended due date.
• Maximum 25%.
• Minimum for returns more than 60 days late: for returns due after December 31, 2025 (which includes 2025 returns), the minimum is $525 or 100% of the unpaid tax, whichever is less.

This is the expensive one, which is why filing quickly matters even if you can't pay.

The failure-to-pay penalty

• 0.5% of the unpaid tax for each month or part of a month, counted from the original April 15 due date.
• Maximum 25%.
• It drops to 0.25% a month during an approved payment plan if you filed on time. If you've missed the extended deadline, you don't get that reduced rate.
• It rises to 1% a month if the tax still isn't paid 10 days after the IRS sends a notice of intent to levy.

The combined-month rule

When both penalties apply in the same month, the IRS reduces the late-filing penalty by the late-payment penalty for that month. Instead of 5% plus 0.5%, you'd see 4.5% plus 0.5%, or 5% total for the month. After five months, the late-filing penalty maxes out, but the late-payment penalty keeps running until it hits its own 25% cap.

Interest

The IRS charges interest on unpaid tax from April 15 until it's paid, and it charges interest on the penalties too. The rate for individuals is set quarterly and compounds daily. For October through December 2026, it's 7% a year (it was 6% for April through June 2026 and 7% for July through September). Interest can't be waived for reasonable cause, but it goes down automatically if a penalty is removed.

Worked example: filing about 2½ months late

This is an example with made-up numbers, not a real client. Federal only.

Morgan extended a 2025 return, paid nothing by April 15, 2026, and owes $10,000. Morgan files and pays on January 5, 2027, about 82 days after October 15.

	Amount
Failure-to-pay penalty: 9 months or partial months since April 15 × 0.5%	$450
Failure-to-file penalty: 3 months or partial months since October 15 × 4.5% (5% minus the 0.5% overlap)	$1,350
Interest from April 15 (6% for Q2 2026, then 7%, compounded daily)	about $499
Total added to the $10,000	about $2,299

Because the return is more than 60 days late, the $525 minimum applies, but the calculated $1,350 is already higher, so it doesn't change anything here. Interest on the penalties themselves would add a little more. If Morgan had filed on October 15 and paid nothing, the late-filing penalty would have been zero. That's the case for filing quickly.

Can the penalties be removed?

Often, yes. There are three paths.

1. Automatic Exemption from Penalty (AEP). This is new. Starting with 2025 tax-year returns, if you filed and paid on time for the three prior years, the IRS says it won't assess the failure-to-file or failure-to-pay penalty when your original return is processed. You'll get a letter saying so, and you don't have to ask. You still owe the tax and the interest.
2. First Time Abate (FTA). For earlier years, or if AEP doesn't apply, the IRS's long-standing first-time relief covers taxpayers with a clean three-year history. You request it by phone or in writing (Form 843), and you don't need to explain why you were late.
3. Reasonable cause. If you used ordinary care and still couldn't file or pay on time, relief is decided case by case. The IRS lists examples like fires and natural disasters, being unable to get records, a death or serious illness, and system problems that delayed an e-file or payment. By the IRS's own guidance, relying on a preparer, not knowing the rules, simple mistakes, or lack of funds alone generally don't qualify.

The estimated tax penalty is separate. It generally can't be removed for reasonable cause and isn't covered by first-time relief.

What if I can't pay what I owe?

File anyway, pay what you can now, and set up a payment plan for the rest.

• Short-term plan: up to 180 days to pay in full, with no setup fee. Penalties and interest keep accruing until it's paid.
• Long-term plan (installment agreement): available online if you owe $50,000 or less in combined tax, penalties and interest and have filed all required returns. A setup fee may apply depending on how you apply.

A payment plan doesn't stop interest, but it can head off collection action. If you filed on time, it also cuts the late-payment penalty in half.

What if I'm owed a refund?

There's no late-filing penalty if the IRS owes you money, because both penalties are a percentage of unpaid tax. But there is a clock: to claim a refund on a return you never filed, you generally have to file within 3 years of the original due date. For example, an unfiled 2023 return (due April 15, 2024) generally has to be filed by April 15, 2027 to get its refund. After that, the money is usually gone for good.

Two more reasons to file even if you think you're due money:

• The IRS can hold a refund if it shows other years as unfiled.
• If you're self-employed and don't file, your self-employment income isn't reported to Social Security, so you don't earn credits toward retirement or disability benefits.

What about Arizona?

Arizona follows the same "file later, not pay later" idea, with its own penalties:

• Extensions: Arizona accepts your federal extension. You just check the "filing under extension" box (82F) on your Arizona return. The Arizona extended deadline for 2025 individual returns was also October 15, 2026.
• Paying with an extension: you needed to pay at least 90% of your Arizona tax by April 15, 2026. If you didn't, an extension underpayment penalty of 0.5% a month (maximum 25%) runs from April 15 until paid. It replaces the regular late-payment penalty.
• Late filing: 4.5% of the tax for each month or part of a month late, up to 25%.
• Late payment: 0.5% a month, up to 10%.
• Interest: Arizona uses the federal rate. It's 7% for July through December 2026, compounded annually on January 1.

You can pay Arizona online at AZTaxes.gov. If you're in the Phoenix area, I work with Phoenix-area business owners on both returns.

What should I do right now?

1. File your federal and Arizona returns as soon as possible. Filing stops the late-filing penalty from growing.
2. Pay as much as you can now. Every dollar paid cuts future penalties and interest.
3. Set up a payment plan for any balance you can't pay right away.
4. Watch your mail. Look for an AEP letter, or ask about First Time Abate or reasonable cause if a penalty notice shows up.
5. Make 2026 easier. If you're self-employed, get your estimated payments and books on track so next year's extension is a choice, not a scramble.

Does a tax extension give me more time to pay?

No. An extension only gives you more time to file. The tax was due April 15, 2026 for 2025 returns. Any unpaid balance has been accruing interest and a 0.5% monthly late-payment penalty since then, whether or not you extended.

Can I still e-file after October 15?

Usually, for a while. The IRS accepts e-filed current-year returns until a cutoff in November that it announces each year. If you miss that window, you'll need another filing option, and the penalties keep running in the meantime, so don't wait.

How much is the penalty for filing late on an extension?

Generally 5% of the unpaid tax for each month or partial month after October 15, reduced by the 0.5% late-payment penalty for the same month, up to 25%. If the return is more than 60 days late, the minimum is $525 or 100% of the unpaid tax, whichever is less. If you owe nothing, there's no late-filing penalty.

Before you do anything else

This is general information, not advice for your own tax situation. Your penalties, relief options and Arizona picture depend on your own history and numbers. If you'd like help getting a late return filed and a plan in place, reach out through my contact form. Please don't send tax documents or Social Security numbers through the form; we'll set up a secure way to share them. You can also see how I work.