Many filers discover after having mailed in their Form 1040 that they made a mistake, such as missed deductions or understated income. Not to worry, says tax guru Julian Block. Here, he explains what a filer must do to amend 1040 depending on their error and how to minimize the chance of IRS audits.  

When Form 1040 time rolls around, I receive queries from filers who made mistakes on their 1040s. They want to know how to fix their tax errors, and I tell them not to worry: Usually, they can still set things right after the fact.

This series will respond to a query from a freelance writer based in New York City. Like a lot of other filers, her tax tribulations began when she scanned her already-mailed 1040 and felt a little jolt of panic when she realized that she messed something up. To soothe her, I reminded her that she’s hardly alone. That’s why the Internal Revenue Service offers what it characterizes as an easy way for her to correct filing errors, such as missed deductions or understated or overstated income.

The tool she needs is a two-page form called Amended U.S. Individual Income Tax Return, or Form 1040-X, formerly 1040X (so named, I like to think, because it lets a filer “X-plain” her mistakes). The IRS mandates its use to justify changes to a filer’s original return and compute any resulting refund or balance due.

Claim game. For starters, I reminded her that the 1040-X comes with its own set of tricky rules. What follows are tips on how to fill it out and set things right with the IRS.

First, she must file a separate 1040-X for each year in which she is claiming a refund or acknowledging that she underpaid. This is the case even if she has made a similar mistake in more than one year because a claim filed for one year doesn’t automatically put the IRS on notice that she seeks a refund or that she underpaid in another year. Along with her 1040-X, she should submit any applicable correspondence from the IRS and corrected versions of her 1040s. 

For example, let’s say she forgot to take advantage of the child-care credit (for 2021’s 1040, it’s at Part II, Line 13g), which gives her a tax break on money paid to a caregiver for her children. No problem: Along with 1040-X, she can submit Form 2441, Child and Dependent Care Expenses, just as she would have to claim the credit on her original return. Or, let’s say she needs to correct the number of wages or tax withheld (for 2021’s 1040, it’s Lines 1 and 25) that she reported for the year in question. She should attach a copy of any additional or corrected W-2 forms that she received after she first filed. Suppose her mistake was simply due to her misreading a correct W-2 form. Chances are, the IRS computers will catch it, but she should still send in a 1040-X and explain the error.