When it comes to filing your tax return, you must do so by April 15 to avoid additional interest and penalties. So long as your tax return is postmarked by this date, the Internal Revenue Service will consider your return timely filed.

Timely Filing

Federal income tax returns are due on April 15 of each year, unless the IRS states otherwise. If April 15 falls on the weekend or holiday, the due date is extended to the next business day. The IRS considers a return timely filed if the envelope is addressed correctly and postmarked no later than April 15. If a taxpayer files taxes according to a fiscal year that's different than the calendar year, his return is timely filed if submitted no later than the 15th day of the fourth month following the end of that year.

How to Request an Extension

If a tax return cannot be filed on time, the taxpayer can request an extension. However, the extension only extends the time to file, not the time to pay. If a taxpayer owes Uncle Sam, this means the payment must be submitted by April 15. Failure to do so will result in additional interest and penalty fees. To receive the extension, the taxpayer must complete and submit IRS Form 4868, Application for Automatic Extension of Time to File U.S. Individual Tax Return, by April 15.