"Timely Mailed, Timely Filed" Rule

• As of 2010, as long as you filed your tax return before the IRS deadline (April 15 of the year following the year reported for most individuals), the IRS will not consider your tax return late even if it fails to receive it before the deadline. For example, if you filed just before midnight on April 15 and the IRS received it on April 18, your tax return is not late as long as it is postmarked April 15. Even if your return gets lost in the mail and the IRS receives it on Oct. 15, it will not be considered late.
  
  

Automatic Extensions

• If you anticipate filing late but have not yet passed the filing deadline, you can request an automatic extension by filing IRS Form 4868 by April 15. The IRS will grant you a six-month extension. You don't need to provide a reason -- such requests are granted automatically. An extension will relieve you of liability for late filing, but will not relieve you of any penalties applicable for late payment.
  
  

Late Penalties

• The IRS late penalty for late filing is based on the amount you owe with your return. If you are entitled to a tax refund, or owe the IRS nothing, there is no penalty for late filing. If you owe money with your return, however, the IRS will assess a penalty of 5 percent of the total tax due for every month or part of a month that your return is late, up to a maximum of 25 percent. Once your return is late, however, the "timely mailed, timely filed" rule does not apply -- the IRS will assess the lateness of your return based on when it actually receives it. If you mail your return on May 14 and the IRS receives it on May 17, for example, the IRS will consider your return two months late and assess a penalty of 10 percent.
  
  

Minimum Penalty

• If your tax return is at least 60 days late, the IRS will assess a minimum penalty of either $100 or 100 percent of the amount you owe, whichever is less. This penalty is calculated by days, not months -- if the IRS receives your tax return June 1, for example, the minimum penalty will not be assessed.
  
  

Reasonable Cause Excuse

• The IRS will waive late filing penalties if you can present evidence that you had reasonable cause for your failure to file on time. Lack of money, however, is never considered an excuse. The IRS is quite strict about the excuses it will accept. If you became seriously ill right before the filing deadline, for example, or if a hurricane hit your hometown, the IRS will probably waive your penalty.