Oops! You Made a Mistake on Your Taxes. Here’s How to Fix It

In most cases, you’ll use Form 1040-X to amend a previously filed federal return. If you’re seeking a refund, you typically need to file an amended return within three years after the date you filed the original or within two years after the date you paid the tax due, whichever is later. (The IRS website has additional information on filing an amended return.)

The sooner you file your amended return, the better. “If the amended return comes out in your favor, that’s less time you have to wait until you get the refund,” says Riley Adams, owner of Sequoia Ridge CPAs in Pleasanton, California. On the other hand, if you’ll owe the IRS money after submitting an amended return, filing quickly means “less time you conceivably could have to pay penalties and interest” on the balance, he says. 

Typically, it takes the IRS eight to 12 weeks to process an amended return, though in some cases it can take up to 16 weeks, the agency says.

Method 3: Accept IRS changes for math or clerical errors

Often, the IRS catches and corrects mathematical errors when processing a return. Ditto for many clerical errors, such as entering the wrong federal income tax rate on your return or claiming a deduction that’s higher than the maximum amount allowed.

The agency will mail you a letter to let you know that it has found and corrected an error. If you agree with the changes, you don’t need to file an amended return; you can simply “pay the tax that the IRS has adjusted, or accept the refund they’re going to send,” O’Saben says.

Fortunately for tax filers, a new law — the IRS Math and Taxpayer Help Act — will require the IRS to provide a more detailed notice when it spots an error on a return. The new rules, which take effect in November 2026, require the letter to include:

• A “plain language” description of the error, including the type of mistake and the specific line on your return where it was found.
• An itemized computation of changes made to correct the error.
• The telephone number for the IRS’s automated tax transcript service, which you can call to request a summary of the tax information in your return.
• The deadline for disputing any tax assessed due to the error.

What about mistakes on state tax returns?

Don’t forget about your state return. In most states with an income tax, you start the calculation of your state tax liability with either your federal adjusted gross income or federal taxable income. 

As a result, you might have to amend your state tax return if you fix a mistake on your federal tax return. The process varies from state to state. Check with your state tax agency for more information on how to correct your return.

How to avoid mistakes

There are a myriad of reasons for tax return blunders. Here are some of the most common ones, and steps you can take to avoid them. 

Filing too early. The IRS usually starts accepting tax returns during the third or fourth week of January. This year, it began processing returns on Jan. 26.

There are benefits to filing early, but make sure you have all of your necessary tax forms before submitting your return. Some documents you need to file your return, such as W-2 or 1099 forms from employers or clients, aren’t required to be provided to you until the last day of January, or even later in certain cases. 

Missing tax breaks. If you forget to claim a tax deduction or credit on your return, it’s usually worth the effort to file a superseding or amended return to claim it. 

Adams often sees this happen with small-business owners who fail to deduct certain expenses on their Schedule C, such as advertising costs, car expenses or insurance premiums. “That’s when you want to go back and file an amendment so you can bring down your tax liability,” he says.

Keeping receipts and credit card statements, using a tax preparation checklist, staying up-to-date on new tax laws (like the 2025 measure commonly called the One Big Beautiful Bill) and consulting a tax professional can help you identify all the tax breaks you’re entitled to claim. 

Filing a paper return. If you’ve been filing paper returns your entire life, it may be time to try a tax software program and file electronically, or to hire a tax preparer who does. The software does all the calculations for you and ensures that you completely fill out the necessary forms and include supporting documents.

“When people leave a Social Security number off a return, or their addition doesn’t add up, or their return is not signed, electronically filing a return will avoid those reasons for the IRS to kick it back,” says O’Saben.