Before you start, pull out a copy of your original Form 1040. If your changes are complicated, you may want to fill out a new Form 1040 to simplify the 1040X process. After all, you don't want to make mistakes on top of mistakes.
You can download Form 1040X from the IRS. At the top of Form 1040X, note what tax year's return you are amending. Be sure to include this, or the IRS will not know which return the form applies to. Remember that a tax year is the year before you actually file -- you file your 2007 tax return in 2008.
Fill in your contact information, Social Security number and filing status.
On the form, you write the numbers you put on your original Form 1040, the corrected numbers and the difference between the two numbers. You can make corrections to:
- adjusted gross income
- tax withholding
- refund or liability
On the reverse side of Form 1040X, you will explain the changes you're proposing. Be as detailed as possible, making references to specific line numbers that have changed values.
If your corrections imply a change to another form or schedule, fill out the appropriate form with the new numbers, and include it with your 1040X. For example, if you made a change to your itemized deductions, you would fill out a new Schedule A. Also, remember to include any documentation, such as that "new" W2 you found, receipts and proofs of purchase.
If lines 19-24 show that you owe the IRS some money, write a check and include it with your amended return. Delaying payment can increase your tax bill. Interest and late-payment penalties are not your friends.
Unfortunately, you cannot file Form 1040X online. You have to do it the old-fashioned way: snail mail.
Mail your amended return, additional corrected forms and schedules, documentation and receipts, and a check (if necessary) to either the IRS processing center that has your original Form 1040, or the processing center recommended in the 1040X instructions.
Next we'll take a look at time restrictions on the Form 1040X.