The late filing penalty for Form 1040 depends on the amount of unpaid taxes and how late the return is filed. The IRS charges a failure-to-file penalty on tax returns filed after the due date or the extended due date, unless there’s a reasonable cause for late filing. The penalty is based on the amount of unpaid taxes and how late you file your return. The IRS’s failure-to-file penalty is 5% of your unpaid taxes for each month or partial month your tax return is late, up to a maximum of 25% of your unpaid taxes. If both the failure-to-file and failure-to-pay penalties apply, the IRS reduces your failure-to-file penalty by the amount of the failure-to-pay penalty. If the return is over 60 days late, the minimum failure-to-file penalty is the smaller of $435 or 100% of the tax required to be shown on the return. The IRS provides additional information about late filing and payment penalties in their Topic No. 653 IRS Notices and Bills, Penalties, and Interest Charges.