Tax Extension Calculator
Need more time to file your taxes? This calculator shows your extended deadline (October 15), exactly how much to pay with Form 4868 to avoid penalties, and what it costs if you skip the extension.
Tax Extension Calculator
See your extended deadline and how much to pay now to avoid IRS penalties
File Form 4868 by the original deadline to get an automatic 6-month extension to file (October 15 for most filers). An extension only extends time to file — not time to pay. Pay at least 90% of your total tax by the original deadline to avoid underpayment penalties, then settle the balance by your extension deadline. Interest (about 8% in 2026) accrues on any unpaid balance from the original deadline. This is an estimate; consult a tax professional for your situation.
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Frequently Asked Questions
How do I file a tax extension?+
File Form 4868 with the IRS — online through IRS Free File, by mail, or with any tax software. It gives you an automatic 6-month extension to October 15. It takes about 5 minutes and is free for most filers.
Does a tax extension delay how much I owe?+
No. An extension only pushes back your filing deadline — not your payment deadline. You still must pay at least 90% of your tax by the original April 15 deadline to avoid underpayment penalties and interest. Use this calculator to see exactly what to pay now.
What happens if I miss the October 15 extension deadline?+
If you file late without an extension, the IRS charges a failure-to-file penalty of 5% of unpaid tax per month, up to 25%, plus interest (about 8% annually). If you don't pay on time, you also face a 0.5% per month failure-to-pay penalty — 10x lower than the filing penalty.
Is a tax extension an extension to pay?+
No. The IRS makes this distinction clear: Form 4868 extends time to file, not time to pay. If you can't pay in full, you should still file on time and set up an installment agreement or offer in compromise rather than ignoring the deadline.
How do I file a tax extension?
File Form 4868 with the IRS — online through IRS Free File, by mail, or with any tax software. It gives you an automatic 6-month extension to October 15. It takes about 5 minutes and is free for most filers.
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