How to amend a tax return: whether you missed a deduction or forgot to claim income, the IRS has a way for you to make changes. You will need a computer with internet access, an IRS form 1040x, receipts, your W-2 form, a copy of your tax return, and an explanation. Step 1: Determine when you made the error on your taxes. File an amended return that will give you a refund within three years if you file within one year to avoid penalties. Step 2: Get the most recent version of form 1040x from IRS.gov. Gather any additional documentation to support your changes, like receipts and W-2 forms. Check with your state tax agency for their rules and forms for amending a state return. Step 3: Complete the 1040x, including information from your original tax return and an explanation for each change you are making. Plan ahead, as the IRS estimates that it will take most people three and a half hours to complete the paperwork for amending a return. Step 4: Attach any supporting documentation you have to the 1040x form. Write your name and social security number on the top of each attachment. Step 5: Mail all of your documents to your IRS regional service center, including a check if you owe additional taxes. Step 6: Wait 8 to 12 weeks for the IRS to process your amended return and send you any refund you are due. Did you know that in 1862, President Lincoln and Congress created the first United States income tax to help pay for expenses during the Civil War.