Individuals must file personal taxes by April 15th.
But if for some reason you cannot file your return by April 15th, you can file an extension. This will give you 6 months to FILE the return, until October 15th.
This does not extend the TIME TO PAY. If you owe on your taxes, the balance is still due April 15th. But by filing the extension you can avoid certain penalties (like the Failure to File penalty).
We always recommend you try to file by the original deadline, but sometimes you have to extend because of certain things outside of your control and that's okay.
As a business owner of a Partnership, S-Corporation or C-Corporation you will have to file your Business return by March 15th. If you file an extension this gives you until Sept 15th.