Every year, millions of tax returns contain errors that cost taxpayers money — either through overpaid taxes, missed refunds, or IRS penalties. Here are the ten most common tax filing mistakes and how to avoid them in 2025.
1. Choosing the Wrong Filing Status
Your filing status affects your tax brackets, standard deduction, and eligibility for credits. The five statuses are Single, Married Filing Jointly, Married Filing Separately, Head of Household, and Qualifying Surviving Spouse.
The most common error is filing Single when you qualify for Head of Household, which offers a higher standard deduction ($23,625 vs. $15,750 in 2025) and wider tax brackets. You qualify if you are unmarried, paid more than half the cost of maintaining your home, and have a qualifying dependent.
2. Not Reporting All Income
The IRS receives copies of every W-2, 1099, and K-1 sent to you. Forgetting to report a 1099-INT for $50 in bank interest or a 1099-NEC for freelance work will trigger a notice.
Starting in 2025, payment platforms must issue 1099-K forms for transactions exceeding $600. If you sell goods or services through apps like Venmo, PayPal, or Etsy, expect to receive these forms and report the income.
3. Missing the Standard vs. Itemized Deduction Decision
Under OBBBA, the 2025 standard deduction is $15,750 for single filers and $31,500 for married filing jointly, rising to $16,100 / $32,200 in 2026. Many taxpayers assume they should itemize without doing the math — or vice versa.
Add up your itemizable expenses (state and local taxes up to the OBBBA SALT cap — $40,000 for 2025, $40,400 for 2026, phasing down above $500,000 MAGI toward a $10,000 floor; mortgage interest; charitable contributions; medical expenses over 7.5% of AGI) and compare. Choose whichever is larger. If you are close to the threshold, consider bunching deductions into one year.
4. Math Errors and Typos
It sounds basic, but math errors are one of the top reasons the IRS adjusts returns. Common mistakes include incorrect addition, wrong Social Security numbers, misspelled names, and using the wrong figure from a W-2 or 1099.
E-filing reduces math errors dramatically because the software performs calculations automatically. If you file on paper, double-check every number.
5. Forgetting Estimated Tax Payments
If you are self-employed, have significant investment income, or your withholding does not cover your liability, you must make quarterly estimated tax payments. The deadlines for 2025 are April 15, June 16, September 15, and January 15, 2026.
Failing to pay enough throughout the year triggers an underpayment penalty (currently based on the federal short-term rate plus 3%). You generally need to pay at least 90% of your current year tax or 100% of your prior year tax (110% if your AGI exceeds $150,000).
6. Overlooking Valuable Credits
Tax credits reduce your tax dollar-for-dollar, making them more valuable than deductions. Commonly missed credits include:
- Earned Income Tax Credit (EITC): Worth up to $7,830 for families with three or more children in 2025.
- Child Tax Credit: $2,200 per qualifying child under 17 for 2025 and 2026 (OBBBA raised it from $2,000, made permanent).
- Saver’s Credit: Up to $1,000 ($2,000 if married) for low-to-moderate-income retirement savers.
- Lifetime Learning Credit: Up to $2,000 for education expenses.
If you do not claim credits you are entitled to, you leave money on the table.
7. Incorrect Bank Account Information
If you are expecting a direct deposit refund, one wrong digit in your routing or account number can delay your refund by weeks or send it to the wrong account. Triple-check these numbers before submitting.
8. Missing the Filing Deadline
The 2025 filing deadline is April 15. If you cannot file on time, submit Form 4868 for an automatic six-month extension to October 15. However, an extension to file is not an extension to pay — you must estimate and pay any tax owed by April 15 to avoid penalties and interest.
The failure-to-file penalty is 5% of unpaid taxes per month (up to 25%), which is ten times higher than the failure-to-pay penalty of 0.5% per month.
9. Not Signing and Dating the Return
An unsigned return is treated as if it was never filed. If you file jointly, both spouses must sign. This is another error that e-filing largely eliminates, as the software requires an electronic signature before submission.
10. Ignoring Prior-Year Carryovers
Several tax items carry forward from year to year, and forgetting them means losing legitimate tax benefits:
- Capital loss carryovers: Net losses exceeding $3,000 carry forward indefinitely.
- Charitable contribution carryovers: Donations exceeding 60% of AGI can carry forward up to five years.
- Net operating losses: Losses from a business can offset future income.
Check your prior-year return for any carryover amounts before filing your 2025 return.
Practical Example
Tom is a single freelancer who earned $85,000 in 2025. He forgets to make estimated payments, overlooks the home office deduction ($1,500 simplified method), and files as Single instead of Head of Household (he supports his mother). These mistakes cost him roughly:
- Underpayment penalty: approximately $350
- Missed home office deduction: $360 in tax savings at 24%
- Wrong filing status: approximately $1,200 in higher taxes
Total cost of these errors: roughly $1,910.
Bottom Line
Most tax filing mistakes are avoidable with careful preparation. Use e-filing software to eliminate math errors, review all your income documents before filing, and make sure you are using the correct filing status and claiming every credit and deduction you qualify for. See IRS Publication 17 for a comprehensive guide to individual tax filing requirements.