Math errors are not a reason to amend as the IRS will correct math errors on your return. You don’t need to amend if you discover that you forgot to attach schedules, or made similar mistakes. The IRS will request them if needed.

If you discover that you omitted a Form W-2 or received revised 1099s or K-1s, you are not required to file an amended return. Filing an amended return could reduce penalties and interest when the IRS gets around to matching up your documents however.

Amended returns are filed on Form 1040X within three years from the date you filed your original return, or within two years from the date you paid the tax, whichever is later. Filing an amended tax return does not restart the three-year statute of limitations.

If your amended return shows you owe more tax, the IRS will compute the interest and send you a bill if you don’t include it. If the IRS thinks you owe penalties it will send you a notice, which you can either pay or contest.