8 common mistakes to avoid when filing your taxes

Tax season is officially here and millions of Americans have started filing their tax return, many in hopes of receiving a refund. But some will have to wait longer because of mistakes on their returns.

In 2024, some 2.7 million returns had math errors, according to the IRS.  

While some mistakes can be corrected fairly easily, other errors can result in missed deductions, interest charges or even financial penalties.

Watch out for these eight common filing mistakes that trip up taxpayers.

If you haven’t received all the tax forms you require — or don't even know which you need — you’re not ready to file.

“The most common mistake that you’ll see is that a taxpayer will go to an accountant or go to do their taxes through a self-preparing mechanism and they’ll do it without everything they need,” says Luis Rivero Vazquez, a CPA and former director of tax at Taxfyle.

Make a list of all the forms you should have, including W-2s from all the employers you worked for in 2024 and any 1099 forms you expect from gig work, unemployment, IRAs or investments.

And don't forget the less common paperwork, either, like Form 5498s-SA for health savings account contributions.

"A taxpayer might say, ‘Oh, hey, I’m getting this huge refund, but I forgot my crypto," Vazquez recalls. "Or, I forgot the small investment that I sold that I need to pay taxes on.’”

Not having all the information you need on hand can mean extra time filing, missing out on hefty deductions or even underpaying your tax bill.

Math mistakes are among the most frequent errors the IRS encounters, according to the agency, ranging from basic blunders in adding and subtracting to complex calculations when claiming deductions.

If you catch the error after your file, you may be able to submit an amended return.

If the IRS determines that you underpaid, however, it will likely demand the additional money plus any interest generated since the return was due.

Tax preparation software like H&R Block and TaxAct automate calculations, going a long way to keeping math mistakes from creeping into your return.

Your filing status is key to which deductions you can take and how return is processed. There are five filing options:

• Single: Anyone who is not currently legally married.
• Married filing jointly: Married spouses who are filing a joint tax return.
• Married filing separately: Each partner files an individual return.
• Head of household: An unmarried filer who supports a qualifying dependent, for whom they pay at least half the living expenses.
• Qualifying widow or widower: Allows a surviving spouse to use married filing jointly rates but on an individual return for up to two years following their partner's death.

Picking the wrong filing status could be costly. If you’ve had a big life change like a marriage or divorce, double-check your status before signing your return and make sure your partner (current or soon-to-be-ex) is filing the same way.

According to the IRS, the number one error taxpayers make in their returns is with the child tax credit.

This tax break is worth up to $2,000 per dependent under 17 on 2024 returns, though it starts phasing out once your adjusted gross income hits $200,000 (for single taxpayers) or $400,000 (for married couples filing jointly).  

The refundable part, known as the additional child tax credit, is up to $1,700, which you can receive even if you don't owe taxes. 

But the guidelines can throw some filers. To qualify for the child tax credit, the child must:

• Be under 17 years old at the end of 2024.
• Be the filer's son, daughter, stepchild, foster child, brother, sister, stepbrother, stepsister, half-brother, half-sister, or a descendant thereof
• Be listed as a dependent on the filer's tax return
• Have lived with filer for more than half of 2024
• Not have paid for more than half of their living expenses
• Be a U.S. citizen, U.S. national or a U.S. resident alien  
• Have a valid Social Security number before the due date of your tax return (including extensions)

Using tax preparation software can come in handy here, too, since most fields for these deductions are already programmed in. And you'll be less likely to accidentally claim credits you're not eligible for.

For 2024, the Earned Income Tax Credit is worth up to $7,830 for eligible families with three or more children, for example, or up to $632 for eligible workers without kids.

New parents can also claim the child and dependent care credit to help cover child care expenses: It's worth $3,000 for one qualifying child under 13 and $6,000 for two or more.

If you're going to itemize your return to deduct property taxes, charitable donations, the interest on your mortgage or medical expenses over 7.5% of your adjusted gross income, be sure to have adequate documentation to avoid an issue.

Some deductions, like for student loan interest, are considered "above the line" and don't require itemizing.

April 15, 2025, isn't just Tax Day, it's the last day to make contributions to a traditional IRA or Roth IRA and still have it count for tax year 2024.

You can contribute up to $7,000 — or $8,000 if you were 50 or older in 2024.

If you have a health savings account, you also have until Tax Day to contribute for 2024: HSAs funds are deposited pre-taxed and grow tax-free, as well. If you use the funds or qualified medical costs, you can withdraw the cash tax-free, too.

For 2024, you can contribute up to $4,150 into a HSA if you have self-only coverage or up to $8,300 if you have family coverage.

Even if your math is solid, it's easy enough to switch two numbers on your wife's Social Security number or to type in "four dependents," when you really have three.

Don't rush through filing and be diligent about addressing any changes that occurred in your household in 2024.

If you itemize your deductions, Vazquez recommended paying close attention to the figures you enter for any charitable contributions and medical expenses — as well as to any taxes you’ve already paid through withholding or estimated tax payments.

If you're one of the roughly 50% of taxpayers expecting a refund this year, congratulations!

But if you don't provide banking account and routing information to the IRS or your tax preparer, you'll have to wait six to eight weeks for a paper check to arrive on your doorstep.

Direct deposit can get you your refund in as little as 21 days, according to the IRS.

Some tax-prep companies promise your money even faster: TurboTax users can get their refund deposited into a Credit Karma Money™ checking or savings account up to five days before the IRS.

Now that you've completed your return, the final step is to affix your signature, digitally or in ink. (If you're filing jointly, both spouses must sign the return.)

The IRS likes to remind taxpayers that an unsigned tax return isn't valid.

At the same time, don't rush through to the signature just to get it over, whether you're working with a CPA, tax preparer or software program.

"As a person, I'd want to know 'Does this [figure] agree to an extent with what I was expecting?'" Vazquez said. "If it doesn't," he added, "[Can they] explain to me why I was wrong?"

And, in your haste, don't forget to hit "send" or drop that envelope in the mailbox by April 15, 2025.

Of course, Vazquez cautions, the process isn't truly over until the IRS confirms it received your return.

"Get a confirmation that your return — with your Social Security number attached — was filed on time and got accepted,."

You can do this with your account or tax-prep software, by making an online account with the IRS or checking the Where's My Refund tool.

Once the IRS has acknowledged your return, you can exhale and wait for the process to begin again next year.

At CNBC Select, we work with experts who have specialized knowledge and authority based on relevant training and/or experience. For this story, we interviewed Luis Rivero Vazquez, a CPA and former director of tax at Taxfyle. As of October 2024, Vazquez is now president of RMW Accounting in Miami.

At CNBC Select, our mission is to provide our readers with high-quality service journalism and comprehensive consumer advice so they can make informed decisions with their money. Every tax article is based on rigorous reporting by our team of expert writers and editors. While CNBC Select earns a commission from affiliate partners on many offers and links, we create all our content without input from our commercial team or any outside third parties, and we pride ourselves on our journalistic standards and ethics.

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