Common tax filing mistakes and how to avoid them

Filing your taxes doesn’t have to be stressful—but even small slip‑ups can cost you time, money, or peace of mind. From missing income to choosing the wrong filing status, common tax filing mistakes can delay refunds, trigger IRS notices, or increase what you owe the IRS.

The good news? You can avoid tax filing errors with a little preparation and the right support. Read on to find out what to watch for (including our list of tax mistakes to avoid), how to fix issues if they happen, and when it makes sense to get expert help. 

What happens if you make a mistake on your tax return?

 If you make a mistake on your return, the IRS may fix it automatically or it may reject your return—depending on the type of mistake. 

• If you make a simple error on your tax return, the IRS may reject your e-file submission allowing you to fix it and resubmit it. In other cases, such as small math errors, the IRS may fix it for you and may notify you via mail. A simple tax filing mistake on your tax return can cause delays in your tax refund or affect the amount you owe.      
• If you make a more significant error, such as missing or misreporting income, you may receive an IRS notice explaining what needs to be corrected and whether you owe additional taxes. 

Looking for support? With many tax filing options, H&R Block can help.

What are the most common tax filing mistakes?

Common tax filing mistakes include simple errors such as math mistakes, incorrect Social Security numbers, and missing signatures. Larger issues include unreported income, choosing the wrong filing status, and missing deductions or credits. 

Other common errors include:

• Incorrect income amounts
• Missing forms and documents
• Math mistakes
• Claiming credits you don’t qualify for
• Missing required tax documents
• Failing to keep good tax and financial records
• Filing before getting all tax documents and missing out on credits and deductions

What mistakes should first-time tax filers avoid? 

First-time tax filers should avoid common mistakes like misspelling names, inputting incorrect Social Security numbers, or filing before you have all your tax forms. . 

Other mistakes for new filers include:

• Forgetting to include all sources of income: This mistake is common when money is earned from part‑time jobs, internships, freelance work, or side gigs that don’t come with a traditional W‑2. Even small amounts of unreported income can cause problems later if the IRS receives matching information.
• Overlooking valuable credits and deductions: Missing credits is another frequent tax mistake. First‑time filers may not know they qualify for certain credits and deductions tied to their income and life stage. 

Use our tax prep checklist to help make sure you’ve gathered all relevant documents and to consider common credits and deductions before you file. 

Most common errors when filing IRS Form 1040

Even when you file on time, simple oversights can still lead to delays or IRS follow-up actions. Other tax filing errors on the individual federal income tax return on IRS Form 1040 include:

• Math mistakes (especially for those who file manually)
• Incorrect Social Security numbers
• Omitted income

While these errors are often unintentional, they can still cause refund delays or lead the IRS notices or corrections. To reduce these types of errors, be sure to double check what you’ve entered against your documents. 

Most common mistakes when preparing Schedule C

Self‑employed filers often run into different issues because business income and expenses have more detailed IRS rules than a standard W‑2 return. If you’re self employed, common Schedule C tax mistakes include: 

• Claiming expenses that don’t qualify: Not every expense counts as a business deduction. The IRS requires expenses to be both ordinary and necessary for your business. 
• Claiming expenses for a hobby that doesn’t have a profit motive: The IRS requires you to report all hobby income, but you can’t deduct hobby-related expenses or losses against other income.
• Underreporting income: Failing to report income shown on Forms 1099‑NEC or 1099-K, is another common issue for Schedule C filers. The IRS receives copies of these forms, and any differences with your Schedule C may trigger an audit. 
• Mixing business and personal expenses: Using the same account for both business and personal spending can make it harder to track deductions and may raise concerns if your return is reviewed. Self-employed individuals may co-mingle expenses, such as paying for gas with a business credit card, versus taking the standard mileage tax deduction. 

Learn more about independent contractor taxes.

Most common mistakes on a multi-state tax return

Filing taxes in more than one state can make your return more complex—and that’s often where mistakes happen. Not to mention, each state has its own tax rules, income thresholds, and requirements. Multi-state return mistakes usually involve filing in the wrong state, missing a required return, or allocating income incorrectly. Multi-state filing mistakes include:

• Not filing a return in every state where it’s required, especially if you work out of state or move during the year
• Reporting income incorrectly when it was earned in more than one state

When you have these types of errors, you might receive a notice from a state tax agency asking about missing income or a return that wasn’t filed. You can lower the risk of these mistakes by keeping good records throughout the year. Track where you worked, especially if your job or location changed. 

Because multi‑state tax returns involve more rules and higher likelihood of error, they’re often a sign it’s time to get expert help whether that’s with an H&R Block tax professional or help with online tax preparation. 

What W‑4 withholding mistakes can affect your refund?

Withholding mistakes can impact your tax refund. If your withholding is off, you could owe taxes or receive a smaller refund than expected.

When your W-4 form withholding doesn’t account for all household income or it is outdated, you may run the risk of not withholding the right amount of taxes each pay period. Big life changes—like getting married, having a child, or starting a new or second job—can change how much tax your employer should withhold. To avoid this, review your withholding and your spouse’s withholding at least once a year or after significant life changes. Read more about how to fill out a W-4.

How tax filing mistakes can delay refunds or trigger IRS notices

These tax filing mistakes can trigger delayed refunds (because they may require manual processing) or even IRS notices: 

• Typos
• Simple data entry errors
• Missing signatures
• Incorrect bank account numbers

Filing on paper instead of e‑filing can also slow things down, especially as the IRS continues to move away from paper checks.

Mistakes involving income underreporting are more likely to trigger IRS letters or notices. If you’ve not reported all your income, you could receive a notice such as an IRS CP2000 (underreporter notice).How to avoid tax filing mistakes

Tax season can sneak up on even the most organized households. Use this checklist to help avoid errors before filing your taxes:

• Double-check your Social Security numbers and Tax Identification numbers (yours, your spouse’s, and dependents’)
• Confirm names are spelled exactly as they appear on Social Security cards
• Verify your tax filing status
• Make sure all income is reported (W-2s, 1099s, side income, investment income)
• Review bank account and routing numbers for direct deposit
• Make sure you have all relevant forms (use our tax prep checklist) and schedule
• Check tax calculations (especially if filing by paper)
• Sign and date your return (both spouses if filing jointly)
• Keep copies for your records

Lean on Block’s expertise for an accurate filing! Whether you file with H&R Block Online or with a tax pro, we guarantee 100% accuracy. Learn more about our guarantees. 

How to fix a mistake after filing your tax return

Fixing a mistake after filing your return depends on the type of mistake. 

• With small math errors or typos, the IRS may fix them for you. 
• For situations such as missing income or deductions, you may need to file an amended return to correct the issue. If you’re wondering how to correct a mistake on a tax return, here’s how: Wait for the IRS to officially accept your e-filed return before amending it. If you’re expecting a refund, make sure the money is in your bank account before you file any corrections.

Keep copies of your return and other supporting documents. You may need them if questions come up later. If you’re not sure whether you need to amend your return—or how to respond to an IRS notice—an H&R Block tax professional can help you.

When should you get expert help with tax filing mistakes?

You may want to get expert help when you have left out significant income or tax benefits or receive an IRS audit notice.  If you do receive a notice, expert assistance can be critical if you cannot answer IRS questions accurately or on-time. 

Don’t want to go it alone? H&R Block has the expertise to help you with an IRS notice. 

How H&R Block can help

From avoiding common tax filing mistakes to fixing issues after you file, we’re here to help you get it right—so you can move forward with confidence. H&R Block offers flexible options for filing your taxes.

Whether you choose to file with a tax pro or file online, H&R Block can help you file your taxes so you can get your maximum refund.*

^{*All tax situations are different. Not everyone gets a refund. See hrblock.com/guarantees for complete details.} 

Frequently asked questions about tax filing mistakes

What happens if I file my taxes incorrectly?

If you file your taxes incorrectly, the outcome depends on the type of mistake. Minor issues—like math errors or missing information—are often corrected by the IRS and may simply delay your refund. More serious tax filing errors, such as underreporting income or claiming credits you don’t qualify for, can trigger IRS notices, including an underreporter inquiry, or result in penalties and interest.

To reduce risk, review your return carefully before filing and use e‑filing tools that automatically check for errors. If you receive an IRS notice, responding accurately and on time is key. 

How can I fix a mistake after filing taxes?

The IRS often fixes simple math errors or missing forms on its own and will send you a notice if it makes a correction. However, if the mistake changes your income, deductions, credits, or filing status—and affects how much tax you owe or your refund—you should file an amended return using Form 1040-X. Correcting the error promptly can help reduce penalties and interest if additional tax is due.

If you’re unsure whether or not you should amend your return, consult our tax professionals.

What tax mistakes trigger IRS audits?

Certain common tax filing mistakes are more likely to draw IRS attention. These include:

• Reporting less income than what the IRS has on record
• Claiming credits or deductions you don’t qualify for

The IRS often finds these problems through automated matching systems, not full audits. This usually leads to a notice in the mail. Reporting your income correctly and keeping good records are the best ways to protect yourself.

What mistakes are common when filing self‑employed taxes?

Self‑employed filers frequently make tax filing mistakes related to income reporting and expense deductions. Common issues include:

• Not reporting all non‑W‑2 income
• Overestimating or misclassifying business expenses, like claiming non-qualifying or incorrectly categorized personal expenses as deductions
• Treating a hobby as a business

For example, a freelancer who omits income reported on a 1099 may receive an underreporter inquiry. Reviewing Schedule C requirements and keeping detailed records can help. 

How do I avoid mistakes when filing multi‑state taxes?

Filing taxes in more than one state can make your return more complex—and increase the chance of mistakes—since each state has its own rules, income thresholds, and filing requirements.

To avoid multi-state tax mistakes:

• Track where you lived and worked throughout the year
• Confirm each state’s filing requirements
• Keep documentation that supports income allocation

Because multi‑state rules vary, professional tax support can help ensure accuracy and prevent state tax notices.

What mistakes should be avoided during tax return preparation?

Mistakes that can be avoided during tax return prep include filing too early or rushing through data entry. Missing deductions, choosing the wrong filing status, or failing to review eligibility rules for credits are among the most common mistakes when filing taxes.

Using a tax preparation checklist—double-check your return can help catch issues beforehand.