Most Common Tax Filing Mistakes in 2026 and How to Avoid Them

Every year, the IRS processes over 150 million individual tax returns — and millions of them contain errors that delay refunds, trigger notices, or cost taxpayers money. Some mistakes are as simple as a wrong digit in a Social Security number. Others are strategic errors worth thousands of dollars, like choosing the wrong filing status or missing deductions specific to the 2025 tax year.

The IRS published updated guidance in March 2026 listing the most common return errors it sees during processing. CPA Practice Advisor also analyzed the top mistakes tax professionals are flagging this season. Here are the errors that matter most and exactly how to avoid each one.

This article is for informational purposes only and does not constitute tax advice. Consult a qualified tax professional for your specific situation.

1. Filing Before All Documents Arrive

The most common mistake of the 2026 filing season is also the most preventable: filing before you have received every tax document. Taxpayers eager for their refund submit returns in late January or early February, only to receive a corrected 1099 or a late-arriving K-1 in March.

When the IRS receives income data from employers and financial institutions that does not match what you reported, it generates a CP2000 notice — an underreporter inquiry that can take months to resolve. In 2025, the IRS issued over 4 million CP2000 notices.

How to avoid it: Wait until you have every W-2, 1099, and K-1 before filing. Most tax documents must be mailed by January 31, but corrected forms (like a 1099-B with adjusted cost basis) can arrive through mid-March. If you are still missing a document, see our guide on what to do when you are missing a W-2 or 1099.

The IRS rejects returns when a Social Security number does not match the name on file with the Social Security Administration. This happens more often than you might expect — name changes after marriage, typos, transposed digits, and using a nickname instead of a legal name all trigger rejections.

How to avoid it: Check every SSN on your return against the physical Social Security card. If your name has changed, update it with the SSA before filing. For dependents, verify the number against the child’s card — do not rely on memory.

3. Choosing the Wrong Filing Status

Your filing status affects your tax bracket thresholds, standard deduction amount, and eligibility for credits. The IRS sees two frequent errors:

Single instead of Head of Household. Unmarried parents who pay more than half the cost of maintaining a home for a qualifying child can file as Head of Household, which provides a higher standard deduction ($22,500 vs. $15,000 for 2025) and wider tax brackets. Missing this costs hundreds to thousands of dollars.
Married Filing Separately when Jointly is better. In most cases, Married Filing Jointly produces a lower combined tax bill. Filing separately disqualifies you from the Earned Income Tax Credit, reduces the Child Tax Credit phase-out threshold, and eliminates student loan interest deduction eligibility.

How to avoid it: Run your return under both filing statuses if you are unsure. Most tax software lets you compare the results side by side. For a detailed breakdown of filing status rules, see our filing status explained guide.

4. Missing the New 2026 Deductions and Credits

Several tax provisions changed for the 2025 tax year (filed in 2026), and taxpayers who are unaware of these changes are leaving money on the table:

Increased Child Tax Credit. The credit rose to ~$2,200 per qualifying child under the One Big Beautiful Bill. If your tax software is using the old $2,000 figure, your return is wrong. See our Child Tax Credit guide for 2026 for eligibility details.
Higher SALT deduction cap. The state and local tax deduction cap increased to ~$40,000 for 2025, up from $10,000. Taxpayers in high-tax states who previously could not itemize should re-evaluate. Our SALT deduction guide explains who benefits.
New senior standard deduction bonus. Taxpayers 65 and older may qualify for the new ~$6,000 additional standard deduction. See our senior tax deduction article for details.
US-made vehicle deduction. A new above-the-line deduction for interest on loans used to purchase US-manufactured vehicles. See our US-made vehicle deduction guide.

How to avoid it: Update your tax software to the latest version, which should include current-year rates. If you are working with a tax professional, ask specifically about OBBB changes.

5. Wrong Bank Account Information for Direct Deposit

More than 1.4 million taxpayers experienced refund delays in the 2025 filing season because of incorrect routing numbers, account numbers, or account types (checking vs. savings) on their returns. When the IRS attempts to deposit your refund into an invalid account, the bank rejects the deposit and the IRS must issue a paper check — adding weeks to your refund timeline.

Starting in 2026, the IRS has moved toward phasing out paper refund checks, making correct direct deposit information even more critical.

How to avoid it: Double-check your bank’s routing number and your account number directly from your bank’s website or a voided check. Do not rely on memory. Verify whether the account is checking or savings.

6. Not Reporting All Income

The IRS receives copies of every W-2 and 1099 issued to you. Its Automated Underreporter system matches this data against your return. Common sources of unreported income:

Interest and dividends. Even $10 in savings account interest from a bank you rarely use generates a 1099-INT.
Gig economy income. Rideshare, delivery, freelance, and marketplace sales income reported on 1099-NEC or 1099-K must be included. Our 1099 contractor tax guide covers reporting requirements.
Crypto transactions. Starting with the 2025 tax year, cryptocurrency exchanges are issuing Form 1099-DA. See our crypto tax Form 1099-DA guide for details.
Side income. Tutoring, consulting, or selling items online — all taxable even without a 1099.

How to avoid it: Log in to your IRS account at IRS.gov and check your Wage & Income transcript. It shows every information return filed under your SSN for the tax year.

7. Math Errors and Unsigned Returns

These are the most basic errors, yet the IRS still catches millions of them:

Math errors on paper returns (addition, subtraction, incorrect amounts carried forward from worksheets). E-filing virtually eliminates these because the software performs all calculations.
Unsigned returns. A return without a signature is considered invalid. For joint returns, both spouses must sign. E-filing replaces the physical signature with a PIN or prior-year AGI verification.

How to avoid it: E-file your return. The IRS reports that e-filed returns have an error rate under 1%, compared to roughly 20% for paper returns. If you need help choosing software, see our best tax software comparison.

8. Not Filing at All

The costliest mistake is not filing a return. The failure-to-file penalty is 5% of unpaid taxes per month, up to 25% — ten times worse than the failure-to-pay penalty. Even if you cannot pay what you owe, file your return on time (or file an extension). The IRS offers payment plans that can spread your balance over up to 72 months.

If you owe nothing or are due a refund, there is no penalty for filing late — but you have only three years to claim a refund before it is forfeited to the U.S. Treasury.

The Bottom Line

Most tax mistakes are avoidable with a simple checklist: wait for all documents, verify personal information, choose the right filing status, claim current-year deductions, double-check bank details, report all income, and e-file your return. If you have already filed and discovered an error, you can correct it by filing Form 1040-X (Amended Return).

For a broader look at strategic tax errors that cost thousands of dollars over time, see our in-depth guide on 15 tax planning mistakes to avoid.