As we approach the end of tax season, most taxpayers have either filed their 2017 tax returns or are in the homestretch of getting all their tax information ready for the final push toward the April 17 deadline. Ideally, by gathering all the forms you need early on, you can ensure that your filed return will be complete and accurate without raising any red flags from the IRS.

Inevitably, though, there are situations in which you'll find that you need to make changes to a return that you've already filed. In that case, you'll need to use Form 1040X in order to amend your return formally. That might sound intimidating, but Form 1040X isn't as difficult to use as many taxpayers fear. Below, we'll look at why you might need to amend your tax return and how you can file a 1040X to get things fixed.

Magnifying glass on top of a Form 1040.

Image source: Getty Images.

When do I need Form 1040X?

There are several reasons why you might need to file a 1040X with the IRS. The most common reason is to make corrections on tax returns that you filed on Form 1040, 1040A, 1040EZ, or similar returns for nonresidents. Those changes can be as simple as having forgotten to check a box or as complicated as reworking the math supporting a major deduction or credit. Sometimes, you'll only realize you've left something out when you get an unexpected tax form in the mail that makes your previously filed return incomplete, and that will require you to amend your return.

There are also certain tax elections that you can only make on Form 1040X if the prescribed deadline has already passed. In addition, if the IRS has looked at your return and made adjustments to the numbers that you originally filed, it can be helpful to file an amended return in order to reflect those corrected numbers and make any other changes that are necessary to be consistent with the IRS determination.

The IRS advises that you not file Form 1040X in certain specified situations. First, if you're requesting a refund of penalties and interest, there's a separate form for claiming a refund and request for abatement that's different from the 1040X form. Also, if you want a refund of an overpayment that was used in part to pay for a past-due obligation of your spouse, you should use a special form for what the IRS calls injured spouse allocation.

How does Form 1040X work?

In general, amending your return using the 1040X form is as simple as the IRS could make it. The form gives you a space to put the original amount you reported, the change that you're making, and the correct amended amount. In some cases, that's the only information that you need to provide.

If the changes have to do with a specific tax schedule or related form, then you'll also typically need to provide a new copy of that schedule with the amendment made. For example, if you're changing the amount of itemized deductions that you're taking, then you'll need to enclose a new Schedule A that gives details about those deductions. However, if you're switching from having itemized deductions to using the standard deduction, then you wouldn't need to include Schedule A, because it's not the basis for the new number you're using.

Form 1040X is divided into several parts, and in many cases, you won't need to make changes to all of them. The front page deals with changes to income, deductions, tax liability, and filing status. Personal exemptions and dependents are handled at the top of the back page, along with changes to your election regarding the presidential election campaign fund. You can also put an explanation in the large box on the back page.

How do I file Form 1040X?

To file Form 1040X, sign and date the back side of the form and then mail it to the address that corresponds to where you live, as indicated in the instructions to the form. Bear in mind that you can't electronically file Form 1040X; the IRS accepts only paper returns.

When can I file the 1040X form?

There are deadlines for filing a 1040X. On the front end, you can file a 1040X as soon as the day after you file your original 1040, but most tax experts suggest that it's better to wait until the IRS has accepted and processed the original return before trying to amend it. Jumping the gun can lead to confusion if the IRS hasn't fully processed your original 1040 and then gets an amendment request.

You have up to three years after the original due date of your tax return to amend the return for that year. So if you want to amend your 2014 tax return that was due in mid-April 2015, you'll have until mid-April 2018 to get that amendment in.

Do what you need to do

Amending your return isn't as difficult as it could be, but it's still an extra step that you'll want to avoid if you can. By knowing how Form 1040X works, you'll be prepared to handle those unexpected situations without panicking and instead take care of your tax business promptly and efficiently.