How to Fill Out a 1040X Form for U.S. Tax Returns

Tax preparation is arduous for business owners and mistakes happen—even on tax returns. If you realize you made a mistake on your tax return for this year or previous tax years, you don’t have to file a whole new return or worry about an IRS audit. You don’t have to worry about filing a bunch of tax forms, either.

The only tax form you need to worry about is Form 1040-X, which is for filing an amended tax return.

Here’s a look at what tax Form 1040-X is, when you might need it, and how to file an amended tax return.

What Is IRS Form 1040-X?

Form 1040-X is the tax form you use if you need to correct a previously filed federal income tax return.

Here are some common reasons you may need to file an amended tax return:

• You forgot to claim a tax deduction or income tax credit.
• You need to change your filing status or add or remove a dependent.
• You need to claim additional taxable income on your return.
• You need to remove an expense, deduction, or tax credit you shouldn’t have claimed on your return.

You don’t need to file Form 1040-X:

• If you discover a simple math or clerical error on a recently filed return. The IRS tends to correct those mistakes on its own. It then sends a CP11 or CP12 notice, informing you of the correction and, if necessary, the additional tax you owe or additional refund you can expect..
• If you receive a notice of change from the IRS and agree with their changes. Just keep a copy of the notice so you can start next year’s return with the correct information.

However, you can file an amended tax return if you receive a notice of proposed changes to your tax return—usually an IRS Notice CP2000—and partially agree with the changes. In that case, send your amended tax return to the address shown in the notice to clarify which changes you disagree with.

If you disagree with the IRS’s proposed changes entirely, respond to the IRS with a letter explaining why your original return is correct.

Who Files Form 1040-X?

Form 1040-X is the form used to amend an individual income tax return. So not all small businesses use it. Only business owners who report their company’s income and deductions on Schedule C use Form 1040-X to amend a business return.

Partnerships and LLCs that file Form 1065 use Form 1065-X to amend their returns. S corporations that file Form 1120-S and C corporations that file Form 1120 don’t need to use a special form for federally amended tax returns. They simply use the same form to file their original tax return and check the “amended tax return” box at the top of the first page.

However, suppose a pass-through business files an amended return that impacts the owner or shareholder’s share of income and deductions. In that case, they will issue a corrected Schedule K-1 to the owner or shareholder. This may require the owner or shareholder to file Form 1040-X to correct their tax return for that year.

When to File IRS Form 1040-X

Before filing an amended tax return, you should confirm that the IRS has processed the tax return you need to correct. You can do this by logging into your IRS.gov account or using the IRS’s Where’s My Refund? tool.

Waiting until the IRS processes your state tax return before filing an amended return also ensures the IRS doesn’t get your original return and amended tax return mixed up.

Check your filing status to ensure the previously filed tax return has been processed before filing an amendment. However, don’t wait too long to file an amended return as there’s a limit on the amount of time you have to file an amended return. Here are the limits:

• Within 3 years of the original filing deadline, or
• Within 2 years of paying the tax due for that year, whichever is later

For example, say you filed your 2023 tax return on the original tax filing deadline of April 15, 2024, and paid the tax due on that date as well. In that case, the last day to use Form 1040-X to file a tax amendment or an amended return for the 2022 tax year would be April 15, 2027.

If you’re outside that window, you cannot file an amended return, even if doing so would get you a hefty tax refund.

How to Fill Out Form 1040-X

If you’re not using a tax professional to complete an amended return, the procedure for filing is pretty straightforward. Here’s a step-by-step look at the process.

Step 1: Collect Your Documents

To file an amended return, you need a copy of your original return. You also need any new documents supporting the amendment, such as a new W-2, 1099, or receipts for a deduction you want to claim.

Step 2: Get the Right Forms

In addition to Form 1040x, you’ll also need any additional forms or schedules that the change will impact. For example, suppose you’re amending your return to add a business expense. In that case, you’ll also need a copy of Schedule C.

Make sure you have the forms for the proper tax year. For example, if you’re amending your 2023 return, you need a copy of the 2023 version of Schedule C. You can find prior-year forms and their instructions at IRS.gov.

If your change impacts more than one tax year, you’ll need to file a separate Form 1040x for each tax year.

Step 3: Fill Out Form 1040-X

At the top of Form 1040-X, fill in your basic information, including the tax year you’re amending, your name, Social Security number, home address, phone number, and filing status.

The rest of Form 1040-X is comprised of 3 columns.

1. Column A shows the numbers from your original tax return. Use your previously filed return to complete this column. Keep in mind that when you file a Form 1040-X for a tax year, it becomes your new tax return for that year. So if you need to amend a tax return you’ve amended once before, use the numbers from your last amendment rather than your originally filed return.
2. Column B shows how the amounts from your original return will increase or decrease due to the change you make. For example, say you’re amending your Schedule C to include an additional $2,000 in deductible expenses. In that case, you enter ($2,000) on line 1, column B to show your adjusted gross income decreasing by $2,000.
3. Column C shows the correct amount. Add the numbers from columns A and B and enter the result in Column C.

On lines 16 through 23, you’ll calculate the additional tax you owe or the additional refund due from the IRS. If you’re preparing Form 1040-X manually, you’ll need to refer to the tax table for the year you’re amending to calculate the tax liability for line 6. You can find the tax tables in the Form 1040 instructions for that year.

While it might be tempting to jump ahead to the lines you think might apply to your change, it’s a good idea to complete the form line by line. Some lines require calculations based on other lines you’ve already filled out. If you jump ahead, you could miss a crucial step. So double-check each line as you go to verify whether it applies to your amended return.

You only need to complete Part II of the form if you change the dependents claimed on your tax return.

In Part III of Form 1040-X, provide a clear explanation for your reasons for filing an amended return. Don’t be too concise here. Start with an overall statement, such as “Amending 2023 return to reflect additional business expenses on Schedule C.” Then briefly explain each changed line throughout the form. For example, “Adjusted gross income on line 1 decreased by $2,000, Qualified business income deduction on line 4b decreased by…” and so on.

Sign and date the bottom of the form. Otherwise, the IRS won’t process your amended return. If you file jointly with your spouse, both of you need to sign Form 1040-X. If your accountant or tax preparer files Form 1040-X for you, they will need to fill out the paid preparer section with their information.

If you used tax software like TurboTax or H&R Block to file your original return, you can use the software to amend your tax return. Just log into your account, open the tax return you already filed, and follow the instructions to amend your tax return.

The software will show how to fill out the form, enter the correct numbers, and calculate the tax change before you send it to the IRS directly.

Step 4: File Your Amended Tax Return

With a completed form filled and signed, it’s time to send it and the related schedules to the IRS.

If the tax return you’re amending is from 2019 or later and you electronically filed your original return for that year, you can e-file your federal amended return.

If you need to amend a return from 2018 or earlier, or complete paper forms for the year you’re amending, you’ll need to print Form 1040-X and any related schedules. Mail your forms to the IRS center listed for the state you live in (found on the IRS website or in the IRS instructions for Form 1040-X). You’ll notice there’s no street address listed in the instructions, but don’t worry: The zip code is exclusive to the IRS processing center and identifies it as going to the IRS.

If you’re amending your return in response to an IRS notice, mail your 1040-X and related forms and schedules to the address shown on the notice.

E-filing is always the most secure way to file a tax return, but if you must mail your return, it’s a good idea to use a method that provides proof of mailing. For example, if you mail your amended return via the U.S. Postal Service (USPS), don’t just pop your forms into the nearest mailbox. Instead, send them via certified mail so you have proof that you mailed your amended return on a specific date. This will come in handy if the IRS loses your return and tries to assess more significant penalties and interest than you actually owe.

You can also send the form and attachments via a private delivery service like DHL, FedEx, or UPS. If you go this route, check out the IRS’s Submission Processing Center Street Addresses for Private Delivery Service list for the correct mailing address.

What to Include With Form 1040-X

Other than the forms and schedules impacted by your amendment, you generally don’t have to include anything else with Form 1040-X. For example, don’t include a copy of your original tax return, direct deposit information, IRS notices, or any other tax documents unless you’ve been instructed to do so.

One exception is if the change you’re making involves a form that shows additional income tax was withheld. For example, say you amended your return to include income reported on a 1099-NEC, and that form shows federal income tax withheld on line 4. In that case, you should attach a copy of Form 1099-NEC to the front of Form 1040-X to report additional income.

While there’s a chance you will have a new refund amount, there’s also a chance amending your tax return results in owing more tax. You should pay the additional tax due when filing Form 1040-X. You can make your additional tax payment online via IRS Direct Pay or the Electronic Federal Tax Payment System (EFTPS), or mail a check with a paper form.

There’s no specific due date for paying, but making that payment right away rather than waiting for the IRS to process your amended return and send you a bill minimizes the interest, additional fees, and penalties you’ll owe.

How to Check on the Status of Form 1040-X

Amended returns often take a while to process—especially if you send your forms via mail instead of e-filing. However, you can check on the status of your amendment using the IRS’s Where’s My Amended Return? tool. You’ll need to provide your Social Security Number, date of birth, and zip code to use the tool.

The IRS says it can take at least 3 weeks after you mail or e-file for it to show up in their system and 16 weeks for the agency to process the forms.

However, it may take even longer. If you can e-file, doing so will help ensure your amended return gets processed as quickly as possible.

How Do I Amend My State Return?

If you’re amending your federal return, you’ll likely need to amend your state income tax return as well. Each state tax agency has its own forms and procedures to file an amended tax return, so check with your accountant or other tax professionals, or your state’s department of revenue for forms and instructions. The Federation of Tax Administrators maintains a list of state tax agencies with links to each state’s website.

Many states require you to attach a copy of your amended federal return to your amended state return.

Again, if you used tax software to prepare and then e-filed your original return, the tax filing software can help you file an amended state return as well. Keep in mind, there may be additional e-file fees associated with a second e-filed return.

Ultimately, there are many reasons you might need to file Form 1040x, and millions of people file amended returns each year. It doesn’t matter if you owe tax or not, if you made a mistake on your return, don’t panic. Just use the form and fix it. Be sure to take your time and double-check your math to ensure you get it right this time around.

If after reading this article or Googling “how to fill out a 1040x form for dummies” you still don’t feel comfortable preparing Form 1040x on your own, reach out to a tax professional for sound tax advice. They can answer any questions about amending your return, correct errors, and even fill out the form for you.

This post was updated in December 2024.