Does an extension delay payment?

No. Form 4868 only extends the time to file the return — your balance is still due by April 15 to avoid failure-to-pay penalty and interest.

File anyway and request an IRS Installment Agreement. The failure-to-file penalty (5%/mo) is 10× the failure-to-pay (0.5%/mo).

Are penalties tax-deductible?

No — IRS penalties and interest are never deductible on personal or business returns.

Tax Extension & Late Penalty Calculator

See the dollar cost of filing or paying late — and the savings from filing a timely Form 4868 extension.

Tax extension & late penalty

Balance due

Did you file Form 4868 by Apr 15?

Date return filed

Date balance paid

Interest rate (current IRS short-term + 3%)

How it works

Failure-to-file: 5% per month (or part), capped at 25% — waived if you filed Form 4868 on time and file by Oct 15.
Failure-to-pay: 0.5% per month, capped at 25%; reduces the failure-to-file rate during overlapping months.
Interest: IRS short-term federal rate + 3%, compounded daily (entered as a single annualized rate here).

Assumptions

Federal individual return (Form 1040). State penalties differ.
Doesn't model the minimum failure-to-file penalty when more than 60 days late.
Interest rate is editable — check the current IRS quarterly rate.

Frequently asked questions

Related calculators

These calculators provide estimates for general planning only and are not tax, legal, or financial advice. Always verify with a licensed CPA for your specific situation.