The deadline to file your taxes has come and gone. Twice, even: The original April 17 deadline was extended to midnight April 18 after the Internal Revenue Service's official website crashed and left millions of people frustrated.

If you still weren't able to make the new deadline, though, you are not alone. Some people knew they couldn't make it: The IRS estimated that it received 11.6 million requests for extensions, including one from President Donald Trump. Others simply watched it go by without a plan.

But while missing the deadline, whether on purpose or because it got away from you, is not uncommon, there are a few things you need to know to avoid some serious penalties.

The deadline for an extension was April 18 and, if you asked for one, you'll have until Oct. 15 to file your taxes, the IRS notes. An extension to file, however, generally is not an extension to pay. You must have already paid what you owe by the deadline to avoid a late fee.