Taxpayers who owe tax and file their federal income tax return more than 60 days after the deadline will usually face a higher late-filing penalty. For that reason, the Internal Revenue Service urges affected taxpayers to avoid the penalty increase by filing their return by Thursday, June 14. Ordinarily, the late-filing penalty, also known as the failure-to-file penalty, is assessed when a taxpayer fails to file a tax return or request an extension by the due date. This penalty, which only applies if there is unpaid tax, is usually 5 percent for each month or part of a month that a tax return is late.