How to File an Amended Tax Return When You Made a Mistake

File Form 1040-X to correct mistakes on a return you already submitted

An amended tax return is filed using Form 1040-X (Amended U.S. Individual Income Tax Return). You file it when you discover an error on a return you already sent to the IRS — a wrong income figure, a missed deduction, a calculation mistake, or a credit you forgot to claim. The IRS does not automatically fix these errors for you, and leaving them uncorrected can cost you money or trigger an audit.

You can file an amended return for up to three years back from the original due date. If you owe money as a result of the correction, you pay it with the amended return. If the correction means you overpaid, the IRS will refund the difference or let you explore it to next year's tax bill.

The process is straightforward: gather your original return and the documents that support the correction, complete Form 1040-X, and mail it to the IRS. You cannot file an amended return electronically through most tax software — you must print and mail it, or use a tax professional who can e-file it on your behalf.

Key Takeaways

Form 1040-X is the only form the IRS accepts for amended individual returns, and you must mail it — electronic filing is not available for most taxpayers.
You have three years from the original due date to file an amended return and claim a refund; after that, the IRS keeps any overpayment.
Gather your original return, the documents that support the correction, and your current tax year information before you start Form 1040-X.
The IRS processes amended returns slowly — expect six to eight weeks for them to post to your account, longer if the return requires manual review.
If you discover an error after the IRS has already audited that year, contact the IRS directly rather than filing an amended return.

Gather your original return and supporting documents first

Before you open Form 1040-X, collect the tax return you originally filed. If you filed electronically, log into your tax software account or contact your tax preparer for a copy. If you filed by mail, you can request a transcript from the IRS by calling 800-829-1040 or visiting IRS.gov and selecting "Get Transcript." A tax return transcript shows the information you reported on your original return.

Next, gather the documents that prove the correction. If you are adding income you missed, collect the W-2, 1099, or other income statement. If you are claiming a deduction you overlooked, gather receipts, invoices, or bank statements that show the expense. If you are correcting a calculation error, write down the correct figures and the source of each one.

Keep your original return and these documents in front of you while you fill out Form 1040-X. You will need to reference the original numbers to show what changed and why.

Complete Form 1040-X line by line

Form 1040-X has three columns: Column A shows the original amount you reported, Column B shows the correction amount, and Column C shows the corrected total. You only fill in the lines that changed.

Start at the top of the form. Enter your name, address, and Social Security number exactly as they appear on your original return. Check the box for the tax year you are amending — for example, if you are correcting your 2023 return, check the 2023 box.

Then go through each line of income, deductions, and credits. For any line that changed, enter the original amount in Column A, the correction in Column B, and the new total in Column C. Leave blank any lines that did not change. For example, if you originally reported $50,000 in wages but actually earned $52,000, you would enter 50,000 in Column A, 2,000 in Column B, and 52,000 in Column C on the wages line.

At the bottom of the form, you will see a line for "Net change in tax." This is the difference between what you originally owed and what you owe now. If this number is positive, you owe money. If it is negative, the IRS owes you a refund.

Understand what happens after you mail Form 1040-X

Mail Form 1040-X to the IRS address listed in the form's instructions — the address varies by state. Include a check if you owe money. Do not staple the check to the form; instead, write your Social Security number and "1040-X" on the check and paper-clip it to the front of the return.

The IRS processes amended returns much more slowly than original returns. Expect six to eight weeks for the IRS to post your amended return to your account. If your amended return involves a refund, the IRS will mail you a check or deposit the money into your bank account if you provided direct deposit information on the form.

You can check the status of your amended return by calling the IRS at 800-829-1040 or by using the "Where's My Amended Return?" tool on IRS.gov. Have your Social Security number and the tax year ready when you call.

When to file an amended return versus contacting the IRS directly

File Form 1040-X if you discovered the error yourself and the IRS has not contacted you about that tax year. This is the standard route for most corrections.

Do not file an amended return if the IRS has already sent you a notice about the year you want to correct. Instead, respond to the IRS notice directly. Filing an amended return while the IRS is already reviewing your return can create confusion and delay resolution. Call the number on the notice or contact a tax professional for guidance.

If you owe money and cannot pay it all at once, you can still file the amended return and then set up a payment plan with the IRS. The IRS offers short-term plans (up to 180 days) at no cost and long-term plans (longer than 180 days) for a small setup fee. You can set up a plan by calling 800-829-1040 or through IRS.gov.

Common mistakes to avoid when filing Form 1040-X

The most frequent error is filing an amended return for the wrong tax year. Double-check that you are amending the correct year before you mail the form. If you correct the wrong year, you will have to file another amended return to fix it.

Another common mistake is leaving Column A blank. The IRS needs to see what you originally reported so they can verify the change. Always fill in Column A with the original amount, even if it was zero.

Do not file multiple amended returns for the same tax year unless the IRS instructs you to. If you discover a second error after you have already mailed one amended return, wait for the IRS to process the first one, then file a second amended return if needed. Filing multiple returns at once confuses the IRS and slows processing.

Finally, keep a copy of Form 1040-X for your records before you mail it. The IRS will not return your copy, and you may need it to track the status of your amended return or to explain the correction to a tax professional or lender later.

When to use a tax professional instead of filing yourself

If your amended return involves multiple changes, complex deductions, or business income, consider having a tax professional file it for you. A CPA or enrolled agent can e-file Form 1040-X, which processes faster than a mailed return. They can also help you identify other years that may need correction and may support all the numbers tie together correctly.

You should also use a professional if you are amending a return that was already audited or if the IRS has sent you a notice. A professional can respond to the IRS on your behalf and may be able to resolve the issue without filing a formal amended return.

The cost of hiring a tax professional to file an amended return typically ranges from $150 to $500, depending on the complexity. This is often worth the expense if the correction involves a large refund or if you are unsure whether you have identified all the errors.

Frequently Asked Questions

How far back can I file an amended return?

You can file an amended return for up to three years from the original due date of the return. For example, if you are amending your 2021 return, the important date is April 15, 2024 (three years after the April 15, 2021 due date). After that important date, the IRS will not process the amended return or issue a refund, though you can still file it to correct your records.

Do I have to file an amended return if I owe money?

Yes. If you discover you underpaid your taxes, you should file an amended return as soon as possible. The longer you wait, the more interest and penalties may accumulate. Filing the amended return voluntarily before the IRS contacts you may reduce or eliminate penalties in some cases.

Can I file Form 1040-X electronically?

Most individual taxpayers cannot e-file Form 1040-X through consumer tax software. You must mail it to the IRS. However, a tax professional with an IRS e-file account can e-file it on your behalf. If you use a tax professional, ask whether they can e-file your amended return to speed up processing.

What if I filed an amended return but then realized I made another mistake on it?

You can file another amended return to correct the first one. The second amended return should reference the first amended return and explain the additional correction. Wait for the IRS to process the first amended return before filing the second one, if possible, to avoid confusion.

Will filing an amended return trigger an audit?

Filing an amended return does not automatically trigger an audit. The IRS reviews amended returns like any other return, and most are processed without further contact. However, if your amended return significantly changes your tax bill or involves a large refund, the IRS may ask for documentation to support the change.

This guide is for general information only and is not medical, financial, legal, or other professional advice. For decisions specific to your situation, consult a qualified professional. See our Editorial Policy.