You know that feeling when finish writing an email, press "send" and immediately realize you made a mistake (aka one of the worst feelings ever)?

Once you're done yelling, "Nooooo!" you likely start writing a corrected message.

That's essentially what you have to do if you make a mistake when filing your taxes. Go ahead, freak out for a minute, then get going on fixing the problem.

On its website, the Internal Revenue Service says your next step depends on the mistake you made:

"Many mathematical errors are caught in the processing of the tax return itself so you may not need to correct these mistakes," the website says. If you forgot to attach a schedule (forms you need to prepare in addition to your tax return, which the IRS requires for certain types of income or deductions), the IRS will reach out to you and ask for the missing information.

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In some cases, like if you didn't report all your income or you forgot to claim a credit, you will need to file an amended return.

What's an amended return, you ask? It's a little like a do-over. Form 1040X looks a bit like its sibling, the good ol' 1040. (And by old I mean old -- the 1040 turns 101 this tax season. Happy birthday!)

Using the 1040X, you enter the changes to any incorrect information on your 1040 and explain the reason behind the changes at the end, attaching any supporting documents. For instance, if you forgot to include a W-2 last time, attach it to the 1040X.

You've got a fair amount of time to make these changes, either within three years of when you filed the original return or within two years of when you paid the tax, if you're trying to get a refund or credit. Whichever one of those deadlines is later is the one you have to meet.

Once you've submitted the 1040X, you're looking at eight to 12 weeks for the IRS to process it. Obviously, you'll want to be more careful this time, so if you're uncertain about the changes you need to make, it's probably a good idea to seek the help of a tax professional.

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