Uh oh, you just sent in your tax return and now you realize you wrote down the wrong SSN for one of your dependents! Or maybe you left out a significant source of business income that you clean forgot about. What do you do now?

File an amended return. It’s easier than you might think, and we’ve got all the info you need to do it right here. Just keep reading.

Why would I need to file an amended return?

You may want or need to file an amended return if you made an error on your original return. For example, you may have:

• Entered your SSN wrong

• Check the wrong box for filing status

• Make a typo on your Form W-2

• Forget to record a charitable donation

You may not need to amend your return for a slight, simple mistake. But you probably do want to consider filing an amended return if:

• You missed a substantial charitable donation or retirement contribution

• You missed some big business deductions

• You failed to report a source of income, like unemployment benefits

• You received a corrected form from your financial institution or employer

• You entered the wrong SSN for yourself, your partner, or one of your dependents

What about mathematical errors? Usually, the IRS will catch these and fix it for you. You’ll likely get a letter from the IRS explaining what happened, but you don’t need to worry about doing anything about it unless the IRS asks you to.

How long do I have to file the amended return?

In general, you have three years to file an amended tax return, or two years if you’ve already paid your original return. But we wouldn’t recommend waiting around. As soon as you realize you made a mistake, file the amendment.

The only exception is if you’re changing your return so you can receive a higher refund. In that case, wait until you receive your original refund, then file the amended return.

How do I file an amended return?

The good news is, you don’t need to start over from scratch. To amend a return, you simply file Form 1040X, Amended U.S. Individual Income Tax return. 

When filling out the form, don’t correct the sections that don’t need to change. For instance, let’s say you just made a mistake with self-employment income on your Schedule C form. In that case, you’d file Form 1040X and the new Schedule C—no other forms or schedules.

Don’t forget to also change your state return, if applicable.

When it comes to sending in your amended return, you’ll have to print and mail it to the IRS, using the address on their website. While you can’t e-file, you can track your amended return’s status via the IRS’ website.

What do I do if I owe more money now?

This is why we recommend filing long before the deadline rolls around. If you realize you underpaid your taxes and now owe more, and the deadline has passed, you may be subject to a penalty and interest on late payment.

But if you underpaid for a good reason—maybe your employer sent you the wrong information, for example—you can send in an explanation with your amended return to ask that the IRS not penalize you. 

You may not have to pay a fee at all if you send in your amended return as soon as possible. The IRS knows everyone makes mistakes.