IRS must help taxpayers understand adjustments with new math error notice requirements

ARTICLE | December 07, 2025

Authored by RSM US LLP

Background–IRS math error notices

A taxpayer diligently prepares and files their annual income tax return, reporting their income, deductions and other financial information for the year. The return was filed on time, and all taxes due were paid. All seems well.

Several months or even years later, the taxpayer receives a letter in the mail from the IRS, containing the words ‘Notice CP11, Math Error on Return – Balance Due.’ The notice states that the taxpayer has made an error on their filed return; the IRS has made an adjustment to correct this error for the taxpayer, but there are now additional taxes due as a result. But what was the error? How did the IRS identify it? The letter may provide a general issue statement, or a list of the return lines where changes have been made, but that might not be enough detail for the average taxpayer to understand the issue and resulting balance due.

What if the taxpayer believes the adjustment (and additional tax due) is incorrect? Notice CP11 may include a section entitled, ‘What you need to do immediately’ for taxpayers who disagree with the adjustment. This would include a warning about the 60-day window to dispute the adjustment and a brief explanation of appeal rights. However, sometimes this section is omitted, leaving it up to the taxpayer to research the Notice requirements, contact the IRS and generally figure out how to dispute the adjustment.

The IRS is generally restricted from making additional assessments to certain filed returns, including income tax returns, without first providing taxpayers an opportunity to dispute the adjustments in the United States Tax Court, under Internal Revenue Code (Code) section 6213. However, the math error procedures under section 6213(b) allow the IRS to summarily assess additional tax based on an adjustment due to a mathematical or clerical error by providing taxpayers with a 60-day response time and no right to petition the Tax Court. This makes math error notices a simpler option for the IRS to make adjustments and assess tax due in a shorter timeframe. Although Notice CP11 does often include information about the 60-day response timeframe, section 6213(b) does not specifically require taxpayers to be notified of this deadline.

It should be noted that two other varieties of IRS math error notices also exist: the neutral Notice CP13, Math Error on Return – No balance due; and the more favorable Notice CP12, Math Error Resulting in Overpayment. Both of these notices can suffer from the same possible issues as Notice CP11, sometimes lacking a clear explanation of what error occurred, and what to do about it.

As daunting as receiving a Notice CP11 may be for the taxpayer, there is still one worse possibility: that the IRS sent out a math error notice, and the taxpayer never received it. In this case, the taxpayer may only become aware of assessed tax due if the IRS starts sending balance due reminders or collection letters–well after the sixty-day response window when the math error adjustment could have been challenged.

The TAS, as an independent organization within the IRS, monitors common problems and misunderstandings that arise between taxpayers and the IRS. When a problem is recurring or systemic, TAS provides suggestions, including legislative proposals, for improvements to IRS policies and procedures. Math error notices have been a frequent subject of discussion on TAS news releases and publications. Most recently, the 2025 TAS Purple Book, Compilation of Legislative Recommendations to Strengthen Taxpayer Rights and Improve Tax Administration, included three separate proposals (Recommendation #9, #10 and #12) for improving IRS math error notices.

Specifically, Recommendation #9 states:

Legislative history

H.R. 998, Internal Revenue Service Math and Taxpayer Help Act, was originally introduced by members of the House Ways and Means Committee in February 2025 and ultimately passed through both houses of Congress with bipartisan support. On Dec. 1, 2025, President Trump signed the bill into law.

H.R. 998 has incorporated the proposed changes from Recommendation #9 almost in its entirety by amending section 6213(b)(1) to add new requirements for valid math error assessments. The TAS suggestion of sending all math error notices by certified or registered mail has been incorporated to a lesser degree, directing the Secretary of the Treasury to begin a pilot program within eighteen (18) months after the law’s enactment sending a portion of notices by certified or registered mail, and reporting to Congress on any changes in the number of notices, taxpayer responses and successful abatement requests.

The remainder of the changes to section 6213(b) will also not take effect immediately, as the language applies to IRS notices sent 12 months after the date when the law was enacted. Therefore, notices should begin reflecting the updated requirements in December 2026.

New notice requirements

Under H.R. 998, math error notices will be required to include a new level of specificity about the alleged math error by providing a plain-language explanation of the type of error, the corresponding section, a description of the nature of the error and the specific line of the return where the error occurred. Additionally, the updated notices must include an ‘itemized computation of any direct or incidental adjustments to be made to the return in connection with the error,’ including changes to income, deductions, credits, tax due, etc. In other words, when an adjustment changes other sections of the return beyond the error itself, the notice will have to detail all of the changes, and not just the specific error.

In addition to providing more details about the error itself, the new law will require notices to be sent to the taxpayer’s last known address, which may reduce the number of notices that are sent but never received by taxpayers.

Finally, H.R. 998 requires the updated notices to specifically list the due date for any abatement request; the date will be in a bold, larger font and marked on the first page of the notice for increased visibility. The notice will also need to provide the phone number for IRS automated phone transcript requests, so that taxpayers can obtain more information before responding.

Abatement request procedures

The language added to section 6213(b) also includes a new section about notice of abatement. In the event that a taxpayer receives a math error notice and timely requests abatement, H.R. 998 will require the IRS to send a letter to the taxpayer’s last known address, describing the abatement in plain language and providing a detailed computation of any adjustments made. This was not among the changes requested by TAS, but Congress’ intention with these new provisions is most likely to leave taxpayers better informed about the status of their abatement request.

The last new clause of H.R. 998 directs the Secretary of the Treasury to implement procedures allowing a taxpayer to request abatement of a math error in writing, by telephone, in person or electronically. Currently, abatement requests are usually expected to be made in writing, by responding to the Notice CP11, though it is technically possible to request abatement by calling the IRS or (if available) scheduling an in-person appointment at an IRS Taxpayer Assistance Center. In practice, however, it can be extremely difficult and time-consuming for a taxpayer to reach an IRS representative by phone or in person. At this point, we do not yet have confirmation of what form the electronic abatement request option might take; one possibility would be to allow taxpayers to use the IRS Document Upload Tool (DUT) for the submission of letters or paperwork in response to Notice CP11.

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