The IRS charges penalties if you file late, don't prepare an accurate return, or don't pay on time. The agency may also charge interest on penalties if you don't pay the penalty in full. The best way to stop the meter running on penalties is to file as soon as you can and pay as much as you can. The IRS may reduce the charges if you can show that you acted in good faith or show reasonable cause for non-payment. See this article on penalty relief from the IRS for more information.