The standard deadline is April 15 with a few caveats:If April 15th falls on a weekend then it is the following Monday, unless the following Monday is April 16th. April 16th is a holiday in Washington D.C. (emancipation day) so that makes the deadline April 17th.The extended deadline is October 15th, but as already mentioned, that is a deadline to file, not a deadline to pay. And you need to file a Form 4868 extension form by the first deadline (April 15)