Why Tax Return Mistakes Are So Common

The federal income tax return is one of the most complex financial documents most Americans encounter each year. Form 1040, along with its schedules and supporting forms, requires taxpayers to synthesize information from multiple sources: W-2s from employers, 1099s from clients and financial institutions, brokerage statements, mortgage interest statements, charitable receipts, and more. With so many data points flowing into a single return, errors are remarkably common. The IRS processes over 150 million individual returns each year, and even small percentage error rates translate into millions of affected taxpayers.

At The Reed Corporation, we see recurring patterns in the mistakes taxpayers make, whether they prepared the return themselves using software or had it prepared by another professional. Understanding these common errors helps taxpayers review their returns more critically and avoid costly consequences including delayed refunds, unexpected balances due, and in some cases, IRS notices or audits.

Incorrect or Missing Social Security Numbers

One of the simplest yet most impactful mistakes is entering an incorrect Social Security number for the taxpayer, spouse, or a dependent. The IRS uses Social Security numbers to match income documents (W-2s, 1099s) to the correct return. A single transposed digit can cause the IRS to reject an electronically filed return or, if the return is processed, trigger a mismatch notice months later. When claiming dependents, the dependent’s Social Security number must match IRS records exactly. Errors here can delay or disallow the Child Tax Credit, Earned Income Tax Credit, and dependency exemption.

Filing Under the Wrong Filing Status

Filing status determines the tax brackets, standard deduction amount, and eligibility for various credits and deductions. The five filing statuses are Single, Married Filing Jointly, Married Filing Separately, Head of Household, and Qualifying Surviving Spouse. The most common mistake in this area is claiming Head of Household when the taxpayer does not meet all three requirements: being unmarried (or considered unmarried) on the last day of the tax year, paying more than half the cost of maintaining a home, and having a qualifying person live in the home for more than half the year. Head of Household provides a larger standard deduction and more favorable tax brackets than Single, which makes it tempting to claim, but the IRS actively audits this status.

Not Reporting All Income

Every dollar of income from every source must be reported on the tax return, even if the taxpayer did not receive a 1099 or W-2 for it. Common sources of unreported income include freelance work paid in cash, gig economy earnings below the 1099-NEC reporting threshold, interest from bank accounts, dividends from brokerage accounts, rental income, cryptocurrency transactions, and gambling winnings. The IRS receives copies of all information returns (1099s, W-2s, K-1s) filed by payers, and its automated matching system compares these documents against the amounts reported on the taxpayer’s return. Any discrepancy triggers a notice, typically a CP2000, which proposes additional tax plus interest.

Taxpayers who receive income from multiple sources, including creators, real estate agents, and other independent professionals, should maintain a running total of all income received throughout the year rather than relying solely on 1099 forms to arrive in January.

Math Errors and Transcription Mistakes

Despite the prevalence of tax software, math errors remain surprisingly common, particularly among taxpayers who enter data manually. Transposing numbers from a W-2, entering a deduction on the wrong line, or miscalculating a credit can all produce an incorrect tax result. The IRS has authority under IRC Section 6213(b) to correct obvious math errors without going through the formal audit process, which means a taxpayer may receive a notice adjusting their return and assessing additional tax without any opportunity to contest the correction through the normal audit procedures.

Missing Deductions and Credits

While some taxpayers overstate deductions, a more common problem, particularly among self-preparers, is failing to claim deductions and credits they are entitled to. Frequently missed tax benefits include:

• The Earned Income Tax Credit, which many eligible taxpayers do not claim simply because they are unaware of it or believe they earn too much to qualify
• Student loan interest deduction, which allows up to $2,500 in interest paid on qualified student loans to be deducted as an adjustment to income
• Educator expenses deduction, which allows teachers and other eligible educators to deduct up to $300 of unreimbursed classroom expenses
• The Saver’s Credit for retirement contributions made by lower and moderate income taxpayers
• Energy efficiency credits for qualifying home improvements under the Inflation Reduction Act
• Business deductions on Schedule C for freelancers who forget to deduct home office expenses, professional development, or business-use-of-vehicle expenses

Incorrect Bank Account Information for Direct Deposit

Taxpayers who choose direct deposit for their refund must enter their bank routing number and account number correctly on Form 1040. An incorrect routing number or account number can cause the refund to be deposited into the wrong account, rejected by the bank, or converted to a paper check, all of which significantly delay receipt. The IRS cannot redirect or reissue a deposit once it has been sent to the bank account specified on the return. Verifying these numbers before filing is a simple step that prevents significant inconvenience.

Not Signing or Dating the Return

A tax return that is not signed is not considered filed. For paper-filed returns, this means an unsigned return can be treated as if it was never submitted, potentially triggering late filing penalties. For electronically filed returns, the signature is provided through a PIN or prior year AGI verification, but errors in these electronic signature methods can cause rejections. Married taxpayers filing jointly must both sign the return. If one spouse is unavailable, a valid power of attorney (Form 2848) can authorize another person to sign on their behalf.

Failing to Report State Refunds or Alimony

If a taxpayer itemized deductions in the prior year and claimed a state income tax deduction, any state tax refund received in the current year may need to be reported as income under the tax benefit rule. This catches many taxpayers off guard because they view the state refund as a return of their own money, not as income. Similarly, alimony received under divorce agreements executed before 2019 is taxable income to the recipient and must be reported on the return. Agreements executed after December 31, 2018 follow different rules under the Tax Cuts and Jobs Act where alimony is no longer deductible by the payer or taxable to the recipient.

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