4 Tax Return Pitfalls to Avoid Before Deadline

Illinois CPAs warn last-minute filers to watch for common mistakes that can trigger IRS scrutiny

Apr. 7, 2026 at 9:12pm

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An extreme close-up of a calculator, pen, and tax forms on a cluttered desk, conveying the intense pressure and complex mechanics of last-minute tax preparation.As the tax filing deadline nears, taxpayers must navigate a maze of forms, receipts, and calculations to avoid costly mistakes.Chicago Today

With the April 15 tax filing deadline just a week away, the Illinois CPA Society is urging taxpayers to be mindful of four common mistakes that can raise red flags with the IRS or Illinois Department of Revenue (IDOR) - inaccurate income reporting, incomplete investment transaction details, unsupported tax credits and deductions, and simple clerical errors. Tax professionals say these issues frequently arise during the final rush to file and can result in information requests, delayed refunds, or additional scrutiny.

Why it matters

Taxpayers who rush through their returns are more prone to making preventable errors that can lead to costly IRS and state tax agency inquiries. Maintaining meticulous records and double-checking all information is crucial to avoiding problems and ensuring a smooth filing process, especially as the deadline approaches.

The details

The most common issues aren't necessarily complex, but they're preventable. Taxpayers should carefully review all income reported on tax forms like W-2s and 1099s, provide accurate cost basis and transaction details for investment sales, maintain documentation to support any credits or deductions claimed, and thoroughly check for simple mistakes like typos or outdated direct deposit information. The Illinois CPA Society notes that the IRS and IDOR scrutinize these areas to discourage abuse and unsupported claims.

  • The April 15, 2026 deadline to file federal and state tax returns or request a six-month extension is just one week away.
  • If an extension is granted, the final deadline to file is October 15, 2026, though any taxes owed must still be paid by April 15 to avoid penalties and interest.
  • Illinois taxpayers who request a federal extension automatically get more time for their state return, but must submit Form IL-505-I by April 15 to avoid late payment penalties.

The players

Illinois CPA Society

A professional association representing more than 20,000 certified public accountants in Illinois, dedicated to enhancing the value of the CPA profession through advocacy, information, education, and connections.

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What’s next

The Illinois CPA Society's free 'Find a CPA' directory can help taxpayers locate a trusted advisor to assist with last-minute filing needs.

The takeaway

Rushing through tax preparation can lead to easily avoidable errors that invite IRS and state scrutiny, so taxpayers should take the time to carefully review all income, investment, credit, and deduction details before submitting their returns, especially as the April 15 deadline approaches.