IRS Form 1040X is used by United States Persons (citizens, residents, nonresident aliens earning income in the US) to amend personal income tax returns that have already been filed with the IRS (Internal Revenue Service).

More often than not this is done with the expectation of getting a refund for money paid incorrectly to the IRS previously, but may also be used to simply keep your income tax record correct and may result in you owing the IRS additional money.

Unlike most of the 1040 series of income tax returns, IRS Form 1040X can not be filed electronically at present, though this may change in the future. Instead, because the 1040X deserves additional scrutiny, it has to be filed on paper and should ideally be sent to the same processing center that you filed the original 1040 with, though you can also send it to another center as described in the instructions of IRS Form 1040X.

Since the filing of the 1040X has to be done manually and the IRS carefully reviews all 1040X submissions, you can expect the process to take several months, so you should take this into consideration when filing. Do not expect a quick return as 1040X amendments always take a while to process.

Once your IRS Form 1040X is received, the internal Revenue Service will carefully scrutinize both your original return as well as the amendments detailed on the 1040X. They will go back over the basis form, like your W-2 or 1098 and 1099 forms to make sure every thing adds up.

Further, they will review all the supporting documentation you include with your 1040X to ensure that it backs your contention. If the IRS is unsure or has questions, they will respond by sending you a letter asking for more information, a step that is likely to extend the duration of the process considerably.

If your IRS Form 1040X is filled out properly and everything matches up and looks good to the IRS investigator looking at your amendment, you can expect to receive your refund in about twelve weeks, though this can take longer.

Basically, the more complicated the amendment is, the longer it will take to review. Therefore it is very much in your best interest to check and double check your 1040X before submitting it and ensure that you also include all relevant documentation supporting your amendment. The easier you make it to confirm your contention the quicker you will get your refund.