Estimate your penalty

Takes about a minute. Nothing you type is sent anywhere.

Who is this for?

Form 1040, the federal individual income tax return.

Tax year

Tax you owe (unpaid balance)

The tax shown on the return that wasn't paid by the deadline.

I filed an extension (Form 4868)

Date the return was filed (or will be)

Haven't filed yet? Leave today's date, or pick a future date to plan ahead.

I'm paying through an IRS payment plan

Date the tax was paid (or will be)

Add an accuracy-related penalty (20%)

Your estimate appears here

Pick who the return is for, enter your numbers, and hit Calculate. You'll get each penalty, interest, and a month-by-month breakdown.

Estimated balance owed to the IRS

Compare ways to pay this balance

Spreading a bill out costs extra. Here's how much each way of paying adds.

Monthly payment

Credit card APR

Personal loan APR

Loan length

What waiting costs

Pay in full on	Total	Extra

See the month-by-month breakdown

Payment schedule

Each payment goes to the tax first, then penalties, then interest, the order the IRS applies them.

Date	Payment	Went to	Balance after

Penalties

Period	Penalty	Rate	Amount

Interest

Period	Days	Annual rate	Interest

This is an estimate. It assumes one payment in full and no prior payments, abatements, or IRS notices. Your actual balance is determined by the IRS. This is not tax advice.

What an extension does, and what it doesn't

Form 4868 gives you an automatic six-month extension to file your individual return. For 2025 returns, it moves the filing deadline from April 15, 2026 to October 15, 2026.

It doesn't give you more time to pay. Your payment was still due on the original April date. Anything you didn't pay by then collects the late-payment penalty and interest from that day on, extension or not. Businesses use Form 7004, and the same idea applies: more time to file, not to pay.

If you file by the extended deadline

File by October and there's no late-filing penalty. On any tax you didn't pay by April, you'll owe two things:

The late-payment penalty: 0.5% of the unpaid tax for each month or part of a month after the April due date, up to 25%.
Interest: compounded daily from the April due date. The IRS rate resets every quarter, and it's 7% for October through December 2026. See the full rate history.

The calculator above already has the extension box checked. Enter what you owed, when you filed, and when you paid.

The 90% rule

Form 4868's instructions include a break worth knowing about. Say at least 90% of your actual tax was paid by the regular April due date, through withholding, estimated payments, or a payment with Form 4868. If you then pay the rest with your return by the extended due date, you're considered to have reasonable cause for the late-payment penalty during the extension period.

In plain terms: pay at least 90% by April, pay the rest when you file by October, and you generally won't owe the late-payment penalty for those months. Interest still applies.

Don't miss the extended deadline. If you file after it, the late-filing penalty starts, figured from the extended due date. That's 5% of the unpaid tax a month, or 4.5% in months when the late-payment penalty also applies, up to 25%. Interest on that penalty runs from the extended due date too.

The late-payment penalty and interest, meanwhile, have been running since April. The late filing penalty calculator shows how the two penalties stack.

Can't pay by October?

File anyway. Filing by the extended deadline keeps the much bigger late-filing penalty off your bill. Then look at a payment plan. While an IRS installment agreement is in effect, the late-payment penalty drops to 0.25% a month for individuals who filed on time, including extensions. The payment plan calculator shows the total cost and your payoff date.

Due dates and extended deadlines for other years are in the deadlines guide.

Questions people ask

Does an extension give me more time to pay?

No. It gives you more time to file, not to pay. Payment was due on the original April date, and the late-payment penalty and interest run from then on anything unpaid.

I filed an extension but paid late. What do I owe?

If you filed by the extended deadline, there's no late-filing penalty. You owe the late-payment penalty, 0.5% a month up to 25%, plus interest, both counted from the April due date. If you paid at least 90% by April and the rest with your return, the late-payment penalty for the extension period generally doesn't apply.

What if I miss the extended deadline?

Then the late-filing penalty applies, figured from the extended due date. It's 5% of the unpaid tax a month, or 4.5% in months when the late-payment penalty also applies, up to 25%.

Do businesses get extensions too?

Yes. Businesses use Form 7004. Like Form 4868, it gives more time to file, not more time to pay.

See every deadline, extensions included

Tax extension penalty calculator