If you have an error or something changes from the time that you file your taxes, typically, you'll need to file an amended return. Now, if you just happened to notice a mathematical error, the IRS will typically correct those and just send you an explanation of what it should have been. There are a number of items that, if those items change, you will need to file an amended return. These items include filing status, amount of total income, number of deductions, and if something with your dependents changes, you'll need to file an amended return. To file an amended return, you'll use Form 1040X, regardless of whether you originally filed 1040, 1040EZ, or 1040A. Amended returns have to be submitted in paper, meaning there is not an option to electronically file an amended return. The 1040X will ask you for the original numbers that you've submitted, the new numbers that you're changing it to, and a reason for the change. You can typically file an amended return within three years of your original filing date, assuming that you've paid all the taxes that are due. However, if you have not paid all the taxes, then the limit is two years for filing an amended return.