Filing your federal income tax return using Form 1040 is an essential task for millions of Americans each year. However, despite improvements in tax software and e-filing systems, a large number of returns still contain errors that can lead to refund delays, audits, or penalties. These mistakes are often preventable and arise from overlooking small but important details.
This blog highlights the most common mistakes taxpayers make on Form 1040 and provides strategies to help you file an accurate and compliant return.
1. Incorrect or Missing Personal Information
One of the most frequent errors is providing incorrect personal details. These seemingly minor mistakes can cause the IRS to reject your return.
- Wrong Social Security Numbers (SSN): Ensure your SSN and those of your spouse and dependents are entered exactly as they appear on Social Security cards.
- Misspelled Names: Match all names to Social Security records. Even one letter off can result in delays.
- Wrong Filing Status: Carefully choose the correct status (e.g., Single, Married Filing Jointly, Head of Household). Selecting the wrong one affects your standard deduction, eligibility for credits, and tax rates.
2. Omitting Income Sources
The IRS receives copies of income documents (e.g., W-2s, 1099s), and failing to report income can lead to underreporting penalties or audits.
- Forgotten 1099s: Include all 1099 forms—such as 1099-INT, 1099-DIV, 1099-B, and 1099-NEC—even if income is small.
- Side gig or freelance work: Even if you were paid in cash or through apps like PayPal or Venmo, you must report self-employment income.
- Unemployment benefits: Form 1099-G must be included if you received jobless benefits.
3. Filing With the Wrong Tax Year Forms
Each tax year has specific forms with updated instructions, credits, and tax brackets. Filing with a previous year’s Form 1040 can lead to confusion or rejection.
Tip: Always check that you are using the correct version of Form 1040 for the tax year you’re filing.
4. Incorrect Standard Deduction or Itemization
Choosing between the standard deduction and itemizing is crucial. Mistakes here can result in overpaying taxes or missing out on deductions.
- Wrong deduction claimed: Ensure you’re claiming the standard deduction only if it exceeds your itemized deductions (mortgage interest, taxes paid, medical expenses, charitable contributions).
- Itemizing without documentation: If you itemize, you must maintain records to support each deduction.
5. Claiming Ineligible Credits or Deductions
The IRS routinely disallows credits and deductions that don’t meet eligibility rules. Common errors include:
- Earned Income Tax Credit (EITC): Incorrectly claiming EITC without eligible dependents or income.
- Child Tax Credit: Claiming a child who doesn’t meet the age, relationship, or residency requirements.
- Education Credits: Using outdated tuition receipts or incorrect Form 1098-T information.
Tip: Use the IRS interactive tools to confirm eligibility for these credits before claiming them.
6. Math Errors and Calculation Mistakes
Although tax software helps minimize arithmetic mistakes, they still happen, especially when filing manually. Common errors include:
- Incorrectly adding income from multiple sources
- Miscalculating self-employment tax
- Entering tax owed or refund amounts on the wrong lines
Solution: Double-check all numbers, use a calculator, and cross-reference each section of Form 1040 and attached schedules.
7. Forgetting to Sign the Return
This is one of the most easily avoided mistakes. An unsigned return is considered invalid and will not be processed by the IRS.
If you’re filing a joint return, both spouses must sign unless one has a valid Power of Attorney form (Form 2848) on file.
Tip: If filing electronically, use the Self-Select PIN or IRS IP PIN to sign digitally.
8. Wrong Bank Information for Direct Deposit
If you’re expecting a refund and opt for direct deposit, entering incorrect banking details can delay your refund or deposit it into someone else’s account.
- Verify your routing and account numbers with your bank
- Double-check account type: Savings vs. Checking
Tip: If you make an error, the IRS may send a paper check instead, which will take longer.
9. Failing to Include Required Forms and Schedules
Many parts of Form 1040 rely on supplementary schedules. Failing to include these forms can result in an incomplete return:
- Schedule 1: For reporting additional income and adjustments (e.g., student loan interest, HSA deductions)
- Schedule 3: For claiming nonrefundable and refundable credits
- Form 8862: For EITC if previously disallowed
Be sure to review IRS instructions or use tax software that prompts you to attach required forms.
10. Filing Late or Missing Deadlines
Filing late without an extension can result in late filing and late payment penalties. The usual deadline is April 15, unless it falls on a weekend or holiday.
Tip: If you need more time, file Form 4868 for an automatic six-month extension, but remember this extends your time to file—not to pay taxes owed.
11. Not Reporting Health Care Coverage Information
Although the federal mandate penalty was removed, some states still require proof of health insurance. Additionally, if you received premium tax credits via the ACA marketplace, you must reconcile them using Form 8962.
Failing to include Form 8962 can delay your refund or cause the IRS to reject your return.
12. Not Updating Address or Filing Status
If you’ve moved during the tax year or your marital status changed, be sure to update your information:
- Use Form 8822 to notify the IRS of an address change
- Select correct filing status based on your status as of December 31
Conclusion: Accuracy Saves Time and Stress
Filing Form 1040 may seem routine, but overlooking key details can cost you time, money, and peace of mind. By carefully reviewing your return, using accurate documentation, and staying updated on current IRS guidelines, you can avoid common mistakes and file confidently.
If your return is complex or you’re unsure about certain deductions or credits, consider consulting a tax professional to ensure you meet all filing requirements and maximize your refund.
