The taxpayer may be subject to several different penalties.
Failure to File
If a taxpayer fails to file on the date the return should have been filed (determined with regard to any extension of time for filing) the taxpayer will be subject to a failure to file penalty unless it is shown that the failure to file a return is due to reasonable cause and not due to willful neglect. This penalty is 5% of the net amount of tax due for each month (or fraction thereof) during which there is a failure to file any return, up to a maximum penalty of 25%. If the return is not filed within 60 days of the due date, the minimum penalty will be the lesser of $135 or 100% of the tax liability on the return (even if there are no unpaid taxes when the return is filed).
If both the “failure to file” and the “failure to pay” penalties apply for the same period, the failure to file penalty (5%) is reduced by the failure to pay penalty (0.5%). This generally results in a 4.5% per month failure to file penalty and a 0.5% per month failure to pay penalty.