CP11A: What It Means and How to Respond
By Forrest Baumhover, CFP®, EA · Last verified September 10, 2026
CP11A is what CP11 becomes automatically the moment an EIC disallowance for a Social Security number, name, or date-of-birth mismatch is one of the math errors on the return — a different underlying problem than a routine recalculation, even though the letter looks nearly identical.
If you got this letter
Got a CP11A in the Mail?
You got this letter because the IRS changed your return and found you owe money. Specifically, one or more of those changes reduced or removed your Earned Income Credit (EIC). That happened because a Social Security number, taxpayer ID number, last name, or date of birth on your return didn't match Social Security Administration records — for you, your spouse, or a child you claimed.
This letter is not the same as a routine math-recalculation letter. The fix here usually means correcting or verifying identity information with the Social Security Administration, not just re-checking arithmetic. If someone on the return doesn't have a Social Security number, the notice will point you toward Form W-7 to get an ITIN (Individual Taxpayer Identification Number) — but an ITIN will not restore your EIC, since EIC specifically requires a valid Social Security number.
You have a real legal right to dispute this: 60 days from the date of the notice to contact the IRS in writing if you disagree and want the change reversed (IRC §6213(b)(2)(A)). Use the address or phone number printed on the notice itself — it has its own section for this. If you ask within 60 days, the IRS must reverse the change (IRC §6213(b)(2)(A)). If you send nothing that fixes the identity mismatch, the IRS can then send your case to audit, where you will have to prove the credit, so send proof of the correct name, number and birth date with your request. There's also a separate, shorter payment due date printed on the notice to avoid additional interest — a different deadline for a different purpose than the 60-day dispute window (IRC §6213(b)(2)(A)). The Math-Error Abatement Clock computes the exact 60-day deadline from the date on your notice (IRC §6213(b)(2)(A)).
If you let the 60 days (IRC §6213(b)(2)(A)) pass without contacting the IRS, the IRS no longer has to reverse the change, and you have to pay the additional tax. The IRS still looks at proof you send later, and the usual path to get money back is a refund claim, and you generally have to file it within 3 years of when you filed the return or 2 years of when you paid the tax, whichever is later. If the IRS moves to collect the tax, you can also still dispute it in a Collection Due Process hearing.
One more thing worth knowing, even though it doesn't change anything about your current letter: a law passed in November 2025 will require future CP11A notices — sent after November 25, 2026 — to spell out the specific line and error in plain language and itemize every number changed, instead of the more general format used today. See the IRS Math and Taxpayer Help Act page for what's changing and when.
What the notice actually says
CP11A tells you the IRS changed your return because of a math error, and that change resulted in a balance due of $5.00 or more. What sets it apart from plain CP11 is mechanical: the IRS code table in Document 6209, Section 9 lists CP11A as the EIC math-error notice with a balance due of $5.00 or more. The sample notice states this directly: EIC was reduced or disallowed "because one or more a social security number, taxpayer identification number, last name, or date of birth was not correct or was missing." That specimen also disallowed a dependent exemption alongside EIC, but personal and dependency exemptions were zeroed out starting with the 2018 tax year and have since been permanently repealed — a current-year CP11A cannot disallow an exemption that no longer exists on the return, so this page does not carry that part of the older specimen forward.
That's a real distinction, not a labeling quirk. A CP11 recalculation can come from almost any arithmetic slip on the return; a CP11A specifically traces to an identity-matching failure against Social Security Administration records for the taxpayer, spouse, or a qualifying child claimed for EIC.
What actually triggered it
This is an IRC §6213(b) math-error assessment: a name, SSN, ITIN, or date of birth entered for the taxpayer, spouse, or a qualifying child failed to match Social Security Administration data, reducing or eliminating EIC and producing a balance due of $5.00 or more.
The most common real-world causes are a typo in a Social Security number, a recent name change (marriage, adoption) that hasn't been updated with the Social Security Administration yet, or a qualifying child whose SSN was missing or wrong on the return (IRC 32(m) allows EIC only for an SSN the SSA issued on or before the return's due date).
Response deadline and what happens if you miss it
Two separate deadlines apply, and confusing them is the single most consequential mistake a practitioner can make on this notice. The first is the IRC §6213(b)(2)(A) math-error abatement right: 60 days from the date of the notice to request that the IRS reverse the change (the request may be written or oral) — the notice and the Internal Revenue Manual's general math-error procedures both confirm it. The IRS must reverse the change if you ask within 60 days, with or without supporting documents, but it then treats an unsupported request as a protest and refers it to Exam Classification (IRM 21.5.4.3.2), so address the SSA mismatch in writing. Miss the 60-day window entirely, and "the change will not be reversed and you must pay the additional tax" — the remedies left at that point include a late reply with substantiation, which the IRS still processes (IRM 21.5.4.4.3), a refund claim within the normal 3-year/2-year limitations period and, if the balance goes to collection, a challenge to the liability under the collection due process procedures (IRM 21.5.4.3).
The second deadline is the specific payment due date printed on the notice to avoid additional interest — a calculated date, not a fixed universal day count, so don't generalize it as a rule. These two deadlines serve different purposes: one preserves your right to dispute the change at all; the other only affects how much interest accrues while you sort it out.
No primary source reviewed names a specific follow-on notice number if you do nothing at all — treat the balance as moving into the IRS's standard collection stream rather than assuming a particular next notice.
What to do next
Verify the actual SSA-matching data before assuming the return was wrong. Confirm the Social Security number, spelling of the name exactly as SSA has it on file, and date of birth for everyone claimed for EIC — a marriage-related name change or a child's SSN that was missing or wrong on the return are common causes that a straight recalculation review would miss entirely. Fixing the SSA record restores EIC only for an SSN the SSA issued on or before the return's due date (IRC 32(m)).
If the fix requires an ITIN application, walk the client through Form W-7 — but confirm before promising anything that an ITIN does not restore EIC eligibility, since EIC requires a valid SSN specifically, not just a taxpayer identification number of any kind. Near day 60 with the SSA mismatch unresolved, ask the IRS now to reverse the change and fix the SSA record in parallel. If an audit then disallows the credit, unlike a math-error change, later claims of that credit need Form 8862 attached.
What people mistake CP11A for
The obvious confusion is with plain CP11 itself — the two letters look and read almost identically, and the same 60-day abatement right (IRC §6213(b)(2)(A)) and payment-deadline structure apply to both. The practical cost of treating them the same is that CP11A's actual defect is an identity-matching failure with the Social Security Administration, not an arithmetic error on the return. A practitioner who responds to a CP11A by simply re-checking the math, without verifying or correcting the underlying SSN/name/DOB data, will not resolve the case — the IRS must reverse the change on a request inside the 60 days, but without proof that fixes the SSA mismatch it refers the case to Exam (IRM 21.5.4.3.2), and a return that computes correctly does not prove the credit.
A second, narrower trap: CP211A is an entirely unrelated notice (it confirms approval of a Form 8868 extension — for an exempt organization's Form 990-series return, or a Form 5330 excise-tax filer) despite the superficially similar number — don't let it come up in a search and lead you to treat it as a CP11 family member.
Common Questions
How is CP11A different from a plain CP11?
CP11A is issued automatically instead of CP11 whenever the underlying math error includes an EIC disallowance caused by a Social Security number, name, or date-of-birth mismatch against Social Security Administration records. The deadlines and payment mechanics are the same as CP11; the underlying defect and the fix are not.
How long do I have to dispute the change?
You have 60 days from the date of the notice to contact the IRS (writing is safest) — a real legal right the IRS has to honor, not just a suggestion (IRC §6213(b)(2)(A)). There's a separate, shorter payment due date on the notice to avoid additional interest, but that one doesn't affect your right to dispute the change within the 60 days (IRC §6213(b)(2)(A)).
Does getting an ITIN fix the problem?
Not for EIC specifically. If a dependent lacks a valid Social Security number, an ITIN can resolve some filing issues, but the notice itself states an ITIN does not restore Earned Income Credit eligibility, since EIC requires a valid SSN.