Suppose you made a mistake on your income tax return? For example, if you excluded income from a 1099 or K-1 that arrived after you filed your return, it is usually not necessary to file an amended return. Usually the IRS matching system catches these errors and the IRS will automatically adjust the amount of tax due and send you a computerized notice. Similarly, if you notice that there was a mathematical error and is also going to be adjusted by the IRS and is not reason for filing an amended return.
If you reviewed your return and noticed that a substantial amount of income was excluded, or was mistakenly left off your return, you should file an amended return as soon as possible.
If you do file a 1040 X, you must file this within 3 years of the date of filing your original return, or within 2 years of the date of payment, whichever is later. The return must be filed as a paper return rather than E-filed.