IRS Notice Library — Practitioner Quick Reference
The Federal Tax Desk | federaltaxdesk.com
When a client calls about an IRS letter, you have minutes to triage it. The notice number in the upper-right corner tells you everything: what the IRS is asserting, how much time you have, and what your client’s rights are.
This library covers the 25 IRS notices practitioners encounter most — organized by category, with response deadlines, first actions, and controlling authority for each. All deadlines run from the notice date printed on the notice, not the date your client received it. That distinction matters every time.
Sources: IRS.gov notice pages (current), IRM (cited by section), IRC (cited by section). Verify IRS.gov for any notice before responding — the IRS updates notice pages periodically.
CATEGORY 1: BALANCE DUE — COLLECTION SEQUENCE
The IRS follows a predictable escalation path. Each notice in this sequence carries more enforcement authority than the last.
CP14 — Notice of Tax Due and Demand for Payment
What triggered it: The taxpayer filed a return showing a balance due but did not pay in full, or the IRS adjusted the account upward and a balance remains.
Response deadline: 21 days from notice date.
Practitioner’s first action: Pull IRS account transcripts (Form 4506-T or online Tax Pro Account) to verify the balance, confirm no payments are in transit, and identify the tax year. If the balance is correct and the client can pay, pay immediately to stop penalty accrual. If the client cannot pay, initiate an Installment Agreement (Form 9465) or evaluate other resolution options before the 21-day window closes.
Controlling authority: IRC § 6303(a) (notice and demand); IRM 5.19.1 (Balance Due Overview); IRS.gov/individuals/understanding-your-cp14-notice
CP501 — First Reminder Notice (Balance Due)
What triggered it: The taxpayer did not respond to CP14. The balance remains unpaid with accrued interest and penalties.
Response deadline: 21 days from notice date.
Practitioner’s first action: Same as CP14 — verify balance via transcripts, then pay or establish a resolution. CP501 is still early-stage; all collection alternatives remain available. Flag that the next notice (CP503) uses stronger language and is followed closely by CP504.
Controlling authority: IRC § 6303(a); IRM 5.19.1; IRS.gov notice index
CP503 — Second Reminder Notice (Balance Due)
What triggered it: No response to CP501. The IRS is escalating urgency. Penalties and interest have continued to accrue.
Response deadline: 30 days from notice date.
Practitioner’s first action: Treat as urgent. Establish a resolution — payment, Installment Agreement, CNC status, or OIC — before CP504 issues. CP504 authorizes the IRS to levy state tax refunds and initiate the Federal Payment Levy Program without further notice. Once CP503 arrives, the window to resolve before enforcement-adjacent action begins is short.
Controlling authority: IRC § 6303(a); IRM 5.19.1; IRS.gov notice index
CP504 — Final Notice Before Levy on State Tax Refund
What triggered it: No response to CP503. The IRS now has statutory authority to levy state tax refunds and certain federal payments (Social Security, federal vendor payments) without further notice under IRC § 6331(d).
Response deadline: 30 days from notice date.
Practitioner’s first action: File Form 2848 immediately if not already on file. Evaluate all resolution options before the deadline — payment in full, Installment Agreement (Form 9465), OIC (Form 656), CNC request, or penalty abatement (Form 843). CP504 is not the CDP-triggering notice (that is LT11/Letter 1058), but it is the last practical opportunity to resolve before the IRS begins passive levies.
⚠️ Note: CP504 authorizes state refund offsets and FPLP levies. It does not authorize bank levies or wage garnishments — those require LT11.
Controlling authority: IRC § 6331(d); IRM 5.19.2; IRS.gov/individuals/understanding-your-cp504-notice
LT11 / Letter 1058 — Final Notice of Intent to Levy and Notice of Right to a Hearing
What triggered it: The IRS has exhausted the collection notice sequence and is now prepared to levy wages, bank accounts, retirement accounts, and other property. LT11 comes from the Automated Collection System (ACS); Letter 1058 comes from a Revenue Officer. Both carry identical legal effect.
Response deadline: 30 days from notice date to request a Collection Due Process (CDP) hearing. This deadline is statutory and unforgiving — missing it permanently forfeits the right to a pre-levy CDP hearing and Tax Court review of the levy.
Practitioner’s first action: File Form 12153 (Request for a Collection Due Process or Equivalent Hearing) within 30 days. Filing timely stops all levy action while the CDP request is pending. At the CDP hearing, you may raise collection alternatives (IA, OIC, CNC), challenge the underlying liability if the client never had a prior opportunity, raise spousal defenses, and appeal an adverse determination to U.S. Tax Court. If the 30-day window has passed, an Equivalent Hearing is still available (one year from notice date) but does not stop levy action and does not preserve Tax Court rights.
⚠️ Critical: Never let the 30-day CDP window expire. Calendar it the day the notice arrives.
Controlling authority: IRC § 6330 (CDP rights); IRC § 6331 (levy authority); IRM 5.11.1; IRS.gov/individuals/understanding-your-lt11-notice-or-letter-1058
CP90 / CP297 — Final Notice of Intent to Levy (Alternative Versions)
What triggered it: CP90 is the version of the final levy notice sent to individuals in certain collection contexts; CP297 is the business entity equivalent. Both carry the same CDP rights as LT11/Letter 1058.
Response deadline: 30 days from notice date for CDP hearing (Form 12153). Same statutory deadline as LT11.
Practitioner’s first action: Identical to LT11 — file Form 12153 within 30 days. Confirm the specific notice type, as CP90 and CP297 are functionally equivalent to LT11 and trigger the same CDP procedures.
Controlling authority: IRC § 6330; IRC § 6331; IRM 5.11.1; IRS.gov notice index
CP523 — Notice of Intent to Terminate Installment Agreement and Levy
What triggered it: The taxpayer defaulted on an existing Installment Agreement — missed a payment, failed to file a required return, incurred a new tax liability, or provided inaccurate financial information.
Response deadline: 30 days from notice date before the IRS terminates the IA and proceeds to levy.
Practitioner’s first action: Determine the cause of default. If a payment was missed, cure the default immediately by bringing payments current. If the default stems from a new liability or unfiled return, address that first. Contact the IRS to request reinstatement before the 30-day window closes — reinstatement is not automatic. If the IA cannot be reinstated, evaluate alternatives (new IA, OIC, CNC). The client retains CDP rights if the IRS proceeds to levy.
Controlling authority: IRC § 6159 (installment agreements); IRM 5.14.1; IRS.gov/individuals/understanding-your-cp523-notice
CATEGORY 2: UNDERREPORTER / MATH ERROR
CP2000 — Notice of Proposed Adjustment for Underpayment/Overpayment
What triggered it: The IRS Automated Underreporter (AUR) program matched third-party information returns (W-2s, 1099s, K-1s, 1098s) against the taxpayer’s filed return and identified a discrepancy. The IRS sends approximately 3 million CP2000s annually — it is the highest-volume substantive notice in the system.
Response deadline: Date shown on the notice — typically 30 days from notice date (60 days if the taxpayer is outside the U.S.).
Practitioner’s first action: Do not treat this as a bill. CP2000 is a proposed adjustment, not an assessment. Pull all relevant third-party documents (W-2s, 1099s, brokerage statements) and compare against what the client reported. Respond in writing — agree, partially agree, or disagree with documentation — by the deadline. If you need more time, request an extension in writing before the deadline. Ignoring CP2000 results in a Statutory Notice of Deficiency (CP3219A), at which point the procedural options narrow significantly.
Controlling authority: IRC § 6201 (AUR authority); IRM 4.19.2 (Automated Underreporter); IRS.gov/individuals/understanding-your-cp2000-series-notice; Pub. 5181
CP2501 — Notice — We’ve Received Your Information Return Data
What triggered it: The AUR program identified a discrepancy but the proposed change is more complex or the IRS needs additional time to evaluate. CP2501 is an early-contact notice that precedes CP2000 in some cases — it notifies the taxpayer of the mismatch before the IRS has calculated a proposed adjustment.
Response deadline: 30 days from notice date to provide information or documentation.
Practitioner’s first action: Respond with documentation addressing the discrepancy. CP2501 is an early intervention opportunity — a well-documented response at this stage can prevent CP2000 from issuing. Gather all relevant third-party documents and prepare a written response.
Controlling authority: IRM 4.19.2; IRS Pub. 5181; IRS.gov notice index
CP11 — Math Error — Balance Due
What triggered it: The IRS corrected one or more errors on the return — typically a math error, an entry that doesn’t match IRS records, or a disallowed credit — and the correction results in additional tax owed.
Response deadline: 60 days from notice date to request abatement of the math error assessment.
Practitioner’s first action: Review the IRS’s correction against the original return and supporting documents. If the IRS is correct, advise payment to stop interest accrual. If the client disagrees, respond in writing within 60 days requesting abatement — this is a statutory right under IRC § 6213(b)(2). Timely written request suspends the assessment; if no response, the IRS proceeds with the corrected amount.
Controlling authority: IRC § 6213(b) (math error procedures); IRM 21.5.4; IRS.gov notice index
CP12 — Math Error — Overpayment
What triggered it: The IRS corrected an error on the return that results in the taxpayer receiving a larger refund or a reduced balance due.
Response deadline: 60 days from notice date to dispute the correction.
Practitioner’s first action: Verify the IRS’s correction is accurate before accepting the adjusted refund. If the change is correct, no action is required — the adjusted refund will issue. If incorrect, respond in writing within 60 days with documentation.
Controlling authority: IRC § 6213(b); IRM 21.5.4; IRS.gov notice index
CP13 — Math Error — No Refund, No Balance Due Change
What triggered it: The IRS corrected an error, but the correction results in neither a refund nor an additional balance due — the net effect is zero.
Response deadline: 60 days from notice date to dispute.
Practitioner’s first action: Review the IRS’s correction. Even if no money is at stake immediately, a math error correction can affect future years (e.g., carryforward amounts, basis calculations). Respond within 60 days if the correction is inaccurate.
Controlling authority: IRC § 6213(b); IRM 21.5.4; IRS.gov notice index
CATEGORY 3: AUDIT / EXAMINATION
CP3219A — Statutory Notice of Deficiency (90-Day Letter)
What triggered it: The IRS has completed its examination (or the AUR process has concluded without agreement) and is proposing to assess additional tax. This is the last notice before assessment — it gives the taxpayer the right to petition the U.S. Tax Court without paying first.
Response deadline: 90 days from notice date (150 days if the notice is addressed to a person outside the U.S.) to file a petition with U.S. Tax Court. This deadline is jurisdictional — missing it means the Tax Court cannot hear the case. The IRS proceeds to assessment and the taxpayer’s only remaining option is pay-and-sue in District Court or the Court of Federal Claims.
Practitioner’s first action: Calendar the 90-day deadline immediately. Evaluate whether to: (1) file a Tax Court petition (buys time and preserves rights), (2) respond with documentation to resolve the matter administratively before the deadline, or (3) pay and pursue a refund claim. Do not let this deadline pass without a decision. File Form 2848 to represent the client before Tax Court if petitioning.
⚠️ Critical: The Tax Court petition deadline is the most consequential hard deadline in routine tax practice. Treat it accordingly.
Controlling authority: IRC § 6212 (notice of deficiency); IRC § 6213 (restriction on assessment); IRM 4.8.9; IRS.gov/individuals/understanding-your-cp3219a-notice
Letter 525 — General 30-Day Letter (Examination Report)
What triggered it: The IRS completed a field or office examination and is proposing adjustments. Letter 525 accompanies Form 4549 (Income Tax Examination Changes), which details the proposed adjustments.
Response deadline: 30 days from notice date to agree, request Appeals consideration, or submit a written protest.
Practitioner’s first action: Review Form 4549 line by line. Do not sign Form 4549 without advising the client of the consequences — signing waives the right to Tax Court review for the agreed items. If the client agrees with all adjustments, signing and paying stops interest accrual. If the client disagrees with any item, file a written protest requesting Appeals consideration within 30 days. Missing the 30-day protest window does not end appeal rights — the IRS will issue a 90-day letter (CP3219A) — but responding promptly at the 30-day letter stage is the most efficient path.
Controlling authority: IRC § 7123; IRM 4.8.9 (examination closing procedures); IRS Pub. 5; IRS.gov notice index
Form 4564 — Information Document Request (IDR)
What triggered it: The IRS examination team requested specific documents, records, or information to support items on the return under examination. The IDR is not a notice in the traditional sense — it is a formal document request issued during an active examination.
Response deadline: Typically 30 days from the IDR date, as specified on the form. Extensions are generally available upon request, but the examining agent must agree.
Practitioner’s first action: Review the IDR carefully. Respond with exactly what is requested — no more, no less. Unsolicited documents can expand the scope of the examination. If the IDR is overly broad or seeks privileged materials, respond in writing addressing the scope concerns before the deadline. Persistent non-response can lead to summons under IRC § 7602.
Controlling authority: IRC § 7602 (examination authority); IRM 4.10.2; IRS.gov notice index
CP75 / CP75A — Exam Initial Contact / EITC Audit
What triggered it: CP75 initiates an audit of the Earned Income Credit (and potentially Head of Household filing status, Additional Child Tax Credit, or Premium Tax Credit). The IRS is holding the refund pending documentation. CP75A is a follow-up requesting additional specific documents.
Response deadline: 30 days from notice date to submit requested documentation.
Practitioner’s first action: Review the documentation checklist attached to the notice (typically includes Forms 886-H-EIC, 886-H-HOH, 886-H-DEP, or Form 4564). Gather qualifying child documentation — birth certificate, school records, medical records, or other residency evidence — and respond by the deadline. The refund remains frozen until the IRS completes its review. Failure to respond results in disallowance of the claimed credits and potential 2-year or 10-year ban on claiming EIC under IRC § 32(k).
Controlling authority: IRC § 32(k) (EIC disallowance); IRM 4.19.14 (EITC examinations); IRS.gov/individuals/understanding-your-cp75-notice
CATEGORY 4: REFUND HOLDS / IDENTITY VERIFICATION
CP05 — Refund Under Review (No Action Required)
What triggered it: The IRS is reviewing the return before releasing the refund — typically to verify income, withholding, tax credits, or business income reported. No discrepancy has been identified yet.
Response deadline: None — no action required at CP05 stage. The IRS will either release the refund, request documents via CP05A, or propose changes.
Practitioner’s first action: Advise the client to wait. Do not send unsolicited documents in response to CP05 — the IRS review is automated and sending documents at this stage does not accelerate the process and may slow it. If the refund has not issued within 60 days of the CP05 date, contact the IRS or consider a Taxpayer Advocate Service referral (Form 911) if financial hardship exists.
Controlling authority: IRM 21.4.2 (refund inquiries); IRS.gov/individuals/understanding-your-cp05-notice
Letter 2645C — Interim Response Letter
What triggered it: The IRS received correspondence or a document from the taxpayer or representative but needs additional time to process it. The 2645C is an interim acknowledgment, not a resolution.
Response deadline: No response required. However, note the promised resolution date in the letter — if that date passes without resolution, contact the IRS or issue a follow-up.
Practitioner’s first action: Log the 2645C and the promised response date. No action needed unless the IRS fails to respond by the stated date. If the case stalls, escalate to the Taxpayer Advocate Service or call the number on the letter. The 2645C does not stop the running of any other deadline — verify that no underlying deadline (e.g., CDP hearing, protest window) is approaching while waiting for the IRS to respond.
Controlling authority: IRM 21.3.3 (Incoming and Outgoing Correspondence); IRS.gov notice index
CATEGORY 5: PENALTY NOTICES
CP161 — Balance Due — Failure to Pay (Business / BMF)
What triggered it: A business entity filed a return (or the IRS filed a substitute for return) showing tax due, and the balance has not been paid. CP161 is the business account equivalent of CP14.
Response deadline: 21 days from notice date.
Practitioner’s first action: Pull business account transcripts. Verify the balance and confirm any deposits or payments the IRS may not have applied. If the balance is correct, evaluate payment in full, an installment agreement, or penalty abatement (Form 843) for the failure-to-pay penalty if reasonable cause exists. First-time penalty abatement may be available under IRM 20.1.1.3.6 if the entity has a clean compliance history.
Controlling authority: IRC § 6651(a)(2) (failure to pay penalty); IRM 20.1.1; IRS.gov notice index
CATEGORY 6: COLLECTIONS — SPECIALIZED
CP71 / CP71A / CP71C — Annual Balance Due Reminder
What triggered it: The taxpayer has an existing balance due and the IRS is sending an annual reminder. CP71 is the standard individual version; CP71A and CP71C are variants for accounts in specific collection statuses.
Response deadline: No statutory deadline attached — these are reminder notices. However, they confirm the balance is still accruing interest and penalties.
Practitioner’s first action: Confirm the account status. If the account is in Currently Not Collectible (CNC) status, CP71 is expected and no action is required — CNC does not resolve the liability, it only suspends active collection. If the client is not in a formal resolution status, use the CP71 as a trigger to review options. The 10-year collection statute (CSED) should be tracked — verify the CSED date on account transcripts.
Controlling authority: IRC § 6502 (collection period); IRM 5.19.1; IRS.gov notice index
Letter 1058 — Final Notice of Intent to Levy (Revenue Officer Version)
See LT11 / Letter 1058 entry under Category 1 — Collection Sequence. Letter 1058 and LT11 are functionally identical and carry the same 30-day CDP deadline.
CATEGORY 7: LIEN
Letter 3172 — Notice of Federal Tax Lien Filing and Your Right to a Hearing
What triggered it: The IRS filed a Notice of Federal Tax Lien (NFTL) in the public records. The lien attaches to all of the taxpayer’s current and future property and rights to property. The lien is now public record and will appear on credit reports and title searches.
Response deadline: 5 business days after the lien filing date shown on the notice to request a CDP hearing (Form 12153). This is a separate CDP right from the pre-levy CDP hearing — it specifically addresses the lien filing.
Practitioner’s first action: Request a CDP lien hearing within 5 business days if the client wants to challenge the lien filing, request lien withdrawal, subordination, or discharge, or propose collection alternatives. At the hearing, you can raise whether the IRS followed lien filing procedures, challenge the underlying liability if never previously addressed, and propose alternatives that would facilitate collection (subordination, discharge) or make the lien unnecessary (full payment, OIC). Lien withdrawal (Form 12277) is available in limited circumstances and erases the public record entirely — distinguish from lien release, which only extinguishes the lien on satisfaction of the debt.
Controlling authority: IRC § 6320 (lien CDP rights); IRC § 6321–6323 (federal tax lien); IRM 5.12.1; IRS.gov notice index
CATEGORY 8: INFORMATION REQUESTS / RETURNS
CP2000 Series — See Category 2 (Underreporter) above.
Letter 105C / Letter 106C — Claim Disallowance Letter
What triggered it: The IRS disallowed a refund claim or credit claim (Letter 105C = full disallowance; Letter 106C = partial disallowance). Common triggers: amended return disallowance, penalty abatement denial, or credit adjustment.
Response deadline: 2 years from the date of the letter to file suit in U.S. District Court or the Court of Federal Claims (after the disallowance, the taxpayer may not file another administrative claim for the same period — the letter starts the refund suit clock).
Practitioner’s first action: Review the stated reason for disallowance. If the disallowance is incorrect, the immediate option is an Appeals protest — file a written protest within 30 days of the letter (voluntary, but opens the administrative Appeals path before litigation). If Appeals consideration is not available or is exhausted, the taxpayer must file suit within 2 years of the disallowance letter date. Log the 2-year suit deadline immediately.
Controlling authority: IRC § 6532(a) (2-year suit limitation after disallowance); IRM 21.5.3; IRS.gov notice index
Notice CP3219A / Letter 531 / Letter 3219 — Statutory Notice of Deficiency Variants
These are all versions of the 90-day Statutory Notice of Deficiency. See CP3219A entry under Category 3 (Audit/Examination). The 90-day Tax Court petition deadline applies to all variants.
QUICK-REFERENCE DEADLINE SUMMARY
5 business days
Letter 3172 — Lien CDP — strict
21 days
CP14, CP501 — Pay or resolve before escalation
30 days
CP503, CP504 — Last pre-enforcement opportunity
LT11 / Letter 1058 / CP90 / CP297 — CDP hearing — statutory, unforgiving
CP523 — IA default — cure or face levy
CP2000, CP2501 — Respond or risk Statutory Notice of Deficiency
Letter 525 — Protest to Appeals
60 days
CP11, CP12, CP13 — Math error abatement right
90 days
CP3219A / Letter 531 / Letter 3219 — Tax Court petition — jurisdictional
Per IDR (typically 30 days)
Form 4564 — Extendable; non-response risks summons
2 years
Letter 105C / 106C — Refund suit limitation period
No deadline
CP05 — Wait; monitor for CP05A
Letter 2645C — Monitor for resolution
CP71 series — Verify CSED; review resolution status
All deadlines run from the notice date printed on the notice, not the date received. All IRM citations current as of 2026. Verify IRS.gov for any notice before responding — the IRS updates notice guidance periodically.
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