If you file your taxes after October 15, which is the final extended tax deadline if you requested an extension by filing Form 4868, you will face failure-to-file penalties. These penalties are typically 5% of your unpaid taxes for each month or part of a month the return is late, capped at 25%. If your return is more than 60 days late, the minimum penalty is either $510 (for 2025) or 100% of the tax owed, whichever is less. If you owe taxes and do not pay them by the original due date in April, you will also face failure-to-pay penalties of 0.5% per month on the unpaid taxes plus interest, which accrues daily. The IRS reduces the failure-to-file penalty by the amount of the failure-to-pay penalty so that combined penalties don't exceed 5% per month. Missing the October deadline can also cause you to forfeit important tax benefits and elections that must be made by that date, such as specific foreign income exclusions or mark-to-market elections. If you are due a refund, filing late generally does not cause penalties, but it may delay your refund. It is always best to file as soon as possible after the deadline to minimize penalties and interest. There is no option to file a second extension after October 15; your return will be considered late past that point. The IRS may waive penalties if you provide a reasonable explanation for filing late.