If you owe tax and don't file on time, the combined late-filing (4 1/2%) and late-payment penalty (1/2%) is 5% of the tax owed for each month, or part of a month, that your return is late and the tax is unpaid, up to 25%. The late-filing penalty continues at 1/2% a month up to 25% on unpaid amounts. If your return is over 60 days late, the minimum penalty is the smaller of $100 or 100% of the tax owed.

There is no penalty for failure to file if a refund is due. To receive a refund, the return must be filed within 3 years of the due date.