Common Tax Filing Mistakes That Can Delay Refunds and Trigger IRS Notices

Tax return errors are often simple, but they can materially delay processing, reduce or offset refunds, and generate IRS notices or assessments. The most common problems identified in IRS guidance include incorrect filing status, missing or incorrect taxpayer identification numbers, omitted income, unsigned returns, incorrect credit claims, and inaccurate bank account information for direct deposit (IRS, IRS, IRS).

A threshold issue is that a return must be complete and properly signed. IRS guidance states that an unsigned paper return is not treated as a valid return, and on a joint return both spouses generally must sign unless a recognized exception applies. That matters not only for filing validity, but also because failure to file a valid return can expose the taxpayer to failure-to-file penalties if the due date passes without a valid submission.

One of the most frequent error categories is taxpayer identification information. IRS guidance repeatedly emphasizes that names and Social Security numbers or other TINs must match official records exactly for the taxpayer, spouse, dependents, and children claimed for credits (IRS). This is especially important because the Code treats certain missing or incorrect TINs as “mathematical or clerical errors” under IRC § 6213(g)(2), including omissions tied to credits such as the child tax credit, earned income credit, education credits, and several newer deductions and credits. When the IRS makes a math-error adjustment, it may assess the additional tax without issuing a notice of deficiency, and the taxpayer generally has no immediate Tax Court petition right unless the taxpayer timely requests abatement within 60 days under IRC § 6213(b)(2).

Incorrect filing status is another recurring problem. IRS publications and notices identify this as a common mistake, particularly where taxpayers improperly claim head of household status (IRS). Filing status affects tax rates, standard deduction, and eligibility for credits, so an error can cascade through the return and produce both refund changes and downstream notices.

Dependent and credit errors are also high-risk. IRS guidance highlights claiming ineligible dependents, failing to include required identifying information, and miscomputing credits such as the earned income credit, child tax credit, and education credits (IRS, IRS). For 2025 returns, the identification rules are especially strict: the child tax credit and additional child tax credit generally require a qualifying child with the required SSN issued by the due date of the return, and the credit for other dependents generally requires the taxpayer or spouse to have a valid SSN or ITIN issued by the due date, including extensions. Because several of these omissions are expressly listed in IRC § 6213(g)(2), they can trigger immediate math-error adjustments rather than ordinary deficiency procedures.

Income omission is another major source of notices. IRS guidance stresses that taxpayers must report all income, even if they did not receive a Form W-2 or Form 1099, and even if the income was not reported on a third-party information return. In practice, omitted wage, interest, dividend, retirement, or gig-economy income often leads to mismatch notices after the return is processed.

Math and computation errors remain common even where the substantive positions are correct. IRS Topic 303 specifically flags incorrect tax calculations, incorrect standard deduction amounts, failure to attach required schedules, and failure to place items on the correct lines (IRS). Electronic filing reduces these issues because the system often rejects returns with common errors before acceptance, which can prevent later processing delays (IRS, IRS).

Refund issues are not limited to return-preparation mistakes. Even where the return is correct, the refund may be reduced by statutory offsets. Under IRC § 6402, the IRS may credit an overpayment against the taxpayer’s federal tax liabilities and may reduce refunds for past-due child support, certain federal agency debts, qualifying state income tax debts, and covered unemployment compensation debts. Those reductions are generally not reviewable in a refund suit against the United States because IRC § 6402(g) bars federal court jurisdiction to restrain or review those offsets, although actions may remain available against the agency or state that received the offset. On joint returns, an injured spouse may seek allocation relief, but that is distinct from innocent spouse relief.

Direct deposit errors can also delay or misdirect refunds. IRS guidance specifically warns taxpayers to verify routing and account numbers and to ensure the account information matches the return information (IRS, IRS). Congress directed Treasury to establish procedures for misdirected direct deposit refunds in IRC § 6402(n), but taxpayers should not assume quick correction if incorrect banking information is entered.

Finally, some delays arise from filing logistics rather than substantive tax law. IRS guidance notes that mailing a return to the wrong address, failing to attach required Forms W-2 or Forms 1099-R showing withholding on paper-filed returns, or failing to include required schedules can all slow processing (IRS).

In short, the filing mistakes most likely to delay refunds or trigger notices are usually procedural rather than aggressive: wrong filing status, TIN mismatches, omitted income, unsupported dependent or credit claims, unsigned returns, math errors, and incorrect refund instructions (IRS, IRS). The legal significance is that some of these errors lead only to ordinary processing delays, while others fall within the math-error regime of IRC § 6213(b) and permit immediate assessment unless the taxpayer timely invokes abatement rights. For refund expectations, taxpayers should also account for mandatory offset rules under IRC § 6402, which can reduce an otherwise valid refund even where the return itself is error-free.