With the Tax Day set for next April 15, 2026, specialized agencies and former officials of Internal Revenue Service (IRS) They identified the five most common mistakes taxpayers make during tax season. Each of these errors has direct consequences: from reduced refunds to penalties and accrued interest.
The volume of declarations that the IRS processes in the weeks leading up to the deadline is often accompanied by a spike in avoidable errors. Experts consulted by specialized media outlets indicate that haste and lack of preparation are the factors that most contribute to submitting forms with incorrect or incomplete data.
The combination of changes to the federal tax code, modifications to deduction limits, and adjustments to available credits makes the 2026 tax season a particularly demanding cycle for those who mechanically repeat the steps of previous years.
Errors in status declaration: The IRS won’t let it pass
The first mistake identified by the specialists is the incorrect selection of the civil status declaration (filing status). That choice determines the applicable tax rate, the standard deduction, and the universe of credits to which the taxpayer can access.
An incorrect selection may result in a higher payment than required, a lower refund than due, or a review of the form by the tax authorities. IRS.
Changes in personal circumstances during 2025—marriage, divorce, birth of a child, addition of a dependent relative, or modifications to shared custody—directly alter the applicable civil status. IRS It provides an online tool to guide taxpayers in that choice, although most are unaware of its existence or do not use it.
Claiming every tax credit available
The second mistake is not claiming all of the tax credits and deductions available. Bill Sweeney, senior vice president of government affairs of AARP, said: “I think the top mistake people make is not fully understanding or taking the time to really research what are all the different deductions and the ways that you can put a little bit of extra money in your pocket that are available to you”.
Sweeney also warned about all the changes introduced by the One Big Beautiful Bill Act: “This would be a good year given that there are these changes to the tax code, to make sure not to assume that what you did last year will convey over to this year”.
Submitting without complete documentation: the risk of an amended declaration
The third documented error is filing the return before having all the necessary supporting documents. The forms W-2 and 1099 are the most frequently omitted documents, either because they didn’t arrive by mail, because the taxpayer misplaced them, or because they were issued electronically without the recipient noticing.
Filing a return with incomplete information then requires amending the original form, a procedure that prolongs processing times and can trigger additional audits.
Mike Faulkender, former commissioner of the IRS, and current co-director of American Prosperity at the America First Policy Institute indicated that there is a simple way to verify the information filed before submitting: “One of the things that I learned last year when I was an IRS commissioner was that if you create an account on irs.gov, you can see everything that’s been filed under your tax ID.”
He added that this resource allows you to identify missing forms without having to request them again from your employer or financial institution.
The omission of secondary income is a frequent consequence of this same problem. Self-employed workers, independent contractors, and participants in the gig economy they receive multiple forms 1099 from different sources, and the possibility that some may go unregistered increases with the fragmentation of income.
Deadline extensions for filing versus extensions for payment
The fourth mistake is one of the most costly in terms of penalties: confusing a extension of time to submit with a extension to pay The extension that the IRS granted to those who request it before April 15 only extends the filing deadline, not the payment deadline.
Faulkender was clear about this: “Remember that even if you claim an extension, the money is owed on April 15.” He added: “You have to actually send a check or have the payment deducted from your account by the filing deadline.”
Taxpayers who cannot pay the full amount before the due date have the option to pay a portion to reduce the interest and penalties calculated on the outstanding balance. IRS applies a late payment penalty of 0.5% monthly on the amount owed, accruing until the debt is paid off.
The fifth error involves technical data that often goes unnoticed: errors in bank details for the direct deposit of the refund, inconsistencies in the number of Social Security of declared dependents, or the failure to correctly report transfers (rollovers) of retirement accounts such as 401(k) the IRA. And rollover indirect payments have a 60-day window to be completed; after that period, the amount may be treated as taxable income plus a 10% penalty for early withdrawal.