If you miss the tax extension deadline of October 16, 2023, you will have to pay failure-to-file penalties that are retroactive to your original filing date, which is typically October 15. The failure-to-file penalty is based on your unpaid taxes, and the IRS charges 5% of your taxes due for every month or partial month your tax return is not filed, up to a maximum of 25% of any taxes owed. If your return is over 60 days late, the minimum failure-to-file penalty is $435 or 100% of the unpaid tax, whichever is less. Additionally, you may owe a late-payment penalty if you didnt pay taxes owed by April 18, 2023, regardless of whether you filed an extension or not. The late-payment penalty is 0.5% of the additional tax owed amount for every month (or fraction thereof) the owed tax remains unpaid, up to a maximum of 25% . If you expect you may owe penalties for filing your tax return late, you should consider speaking with a tax professional before filing.