The Notice Library
Every notice below is explained the same way: what it is, what it is not, how serious, the clock it carries, what ignoring it does, and the first move. Sourced to the IRS's own notice pages and the tax code — checked October 2026.
CP14
Your first bill. The IRS finished your return, the math left a balance, and this notice is the formal demand for it (the law calls it notice and demand, 26 U.S.C. 6303).
CP501
A reminder bill. You owed a balance, the first bill (CP14) didn't produce a payment, and this is the IRS asking again — with interest and penalties still running.
CP503
The second-to-last reminder before levy language starts. Same balance as CP14 and CP501 — the IRS is done asking politely.
CP504
A 'Notice of Intent to Levy' — the IRS says pay immediately or it can levy (take) your state tax refund, and it is now searching for other assets. Issued under 26 U.S.C. 6331(d).
LT11
The Final Notice of Intent to Levy — and the notice of your right to a hearing. This is the letter that starts the most important 30 days in the whole collection ladder.
Letter 1058
The same Final Notice of Intent to Levy as LT11 — the difference is who sent it: Letter 1058 usually comes from a revenue officer (a person working your case), LT11 from the automated system.
CP90
A Final Notice of Intent to Levy for specific kinds of property — including federal payments — and it carries the same Collection Due Process hearing right as LT11.
CP297
The companion version of the final levy notice — a Final Notice of Intent to Levy that carries your Collection Due Process hearing right, issued where the standard LT11/1058 doesn't fit (for example, certain joint or successor accounts).
CP91
The final notice before the IRS levies Social Security benefits through the Federal Payment Levy Program — it can take up to 15% of each monthly benefit payment until the balance is resolved.
Letter 3172
The IRS has filed a Notice of Federal Tax Lien — a public record telling your creditors the government claims your property for a tax balance — and this letter gives you the right to appeal the filing at a hearing.
CP523
Your installment agreement is in default — a missed payment, a new unpaid balance, or a missing return — and the IRS intends to terminate the plan and resume collection, including levy.
CP521
The monthly reminder for your installment agreement: how much you owe, how much to pay this month, and where to send it.
CP71
An annual reminder: you still owe a balance from an earlier year, and the IRS sends this about once a year so the debt doesn't go quiet.
CP161
A request for payment of an unpaid balance — functionally a member of the balance-due family, most often seen on business and employment-tax accounts, but it appears on individual accounts too.
LT16
A collections outreach letter — in plain words, 'we have not heard from you.' An IRS collection unit is asking you to call about an unpaid balance before the account moves to stronger notices.
LT24
A proposal letter: the IRS is offering you a specific payment plan — a monthly amount and terms — and asking you to accept it (often by signing and returning a form) by a printed date.
CP2501
The first letter in the income-mismatch process: the IRS compared your return with what employers, banks, and platforms reported, found a difference, and is asking you to explain it before anything is proposed.
CP2000
A proposed change to your tax return: the IRS's computers matched your return against third-party reports, found a gap, and computed the extra tax, penalties, and interest they say follows. The average proposed balance runs around $5,400.
CP3219A
The statutory notice of deficiency — the famous '90-day letter.' The IRS has formally decided you owe more tax, and this notice is your ticket to the one court that hears tax cases before you pay: the U.S. Tax Court.
CP11
The IRS corrected a math or clerical error on your return and the correction leaves you owing money. Buried in this ordinary-looking notice is an extraordinary right: ask within 60 days and the IRS must undo the assessment.
CP12
The IRS corrected an error on your return and the correction changes your refund — usually the math-error family's good-news branch: a refund is coming, or a bigger one than you expected.
CP13
The IRS changed something on your return and the change nets to zero — no refund, no balance. A record-keeping notice.
CP10
The IRS adjusted your return and applied part or all of your refund to a balance you owe for a different tax year — this notice explains the change and where the money went.
CP21
The IRS made the change you asked for — usually from an amended return or a phone request — and this notice reports the result: a refund, a balance, or neither.
CP22
The IRS changed your account from data it processed — for example, information from an amended return, a corrected document, or an internal adjustment — and the change produced the result this notice shows (a balance, on the CP22A variant).
CP23
An estimated-tax mismatch: the credits the IRS shows for your quarterly estimated payments don't match what your return claimed, and the difference changed your bill or refund.
CP49
Your refund was applied to a tax balance from another year instead of being sent to you. This notice shows the refund, the debt it paid, and what's left of each.
CP75
An audit-by-mail asking for documents: the IRS is examining a specific item on your return — most often the Earned Income Tax Credit, dependents, or education credits — and wants proof before it decides.
Letter 566
The opening letter of an audit by mail: the IRS has selected specific items on your return for examination and is asking for the documents that support them.
Letter 525
The examination report: the IRS has finished its review, proposes specific changes (with a report, usually Form 4549), and gives you 30 days to agree, partly agree, or ask for your case to go to the IRS Independent Office of Appeals.
Letter 531
The notice of deficiency after an examination: the IRS's formal, final determination that you owe additional tax — and your 90-day ticket to petition the U.S. Tax Court before paying.
Letter 5071C
An identity check: the IRS flagged the return filed under your name and froze it until you prove you're you. Verify, and processing resumes; don't, and the return (and any refund) sits suspended.
Letter 4883C
The phone-only sibling of 5071C: the IRS needs you to call and verify your identity before it will process the return filed under your name.
Letter 5747C
The in-person identity letter: because of a data breach or a high-risk flag, the IRS will only verify you face-to-face at a Taxpayer Assistance Center. Your return waits until you go.
CP05
A review notice: the IRS is holding your refund while it double-checks income and withholding from your return against employer and bank reports. It typically asks for nothing and buys itself about 60 more days.
CP05A
The follow-up to a refund review: the IRS now wants specific documents — pay stubs, employer statements, withholding proof — before it releases your refund.
Letter 12C
The IRS can't finish processing your return without something: a missing form or schedule, a health-coverage form (Form 8962 for premium tax credits is the classic), a signature, or a document it names.
CP59
The IRS has no record of your tax return for the year named, and it wants one — or your explanation of why you weren't required to file. The nonfiler program restarted at scale: over two million of these went out in FY2025.
CP518
The final notice in the unfiled-return sequence: file the return named, or the IRS may determine your tax itself from the information it has.
CP2566
A proposed assessment from a substitute for return: since no return arrived, the IRS computed your tax from W-2s and 1099s — and is proposing that figure, usually with penalties.
CP63
The IRS is holding a refund from a year you DID file because it shows earlier returns you did NOT file. File the missing years, and the hold can release.
CP09
The rare IRS letter that might be carrying good news: IRS records suggest you may qualify for the Earned Income Tax Credit but didn't claim it. It includes a worksheet/form to claim it.
The free decoder tells you what the letter means and when it is due. The Kit is the doing: response letters for every notice family, the penalty-relief scripts, the payment-plan and Offer in Compromise reality checks, and the proof habits that keep a sent letter from becoming a lost argument.
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