1. What Is a Notice of Deficiency and Why It Is the Gateway to Tax Court
Notice of Deficiency: Quick Reference
What it is: A notice of deficiency (also called a "90-day letter" or "SNOD -- Statutory Notice of Deficiency") is the IRS's formal notice under IRC 6212 (hedge: verify at IRS.gov and in current IRC text) that it has determined the taxpayer owes additional tax for one or more tax years. It is issued after an examination concludes without agreement between the taxpayer and the IRS on the proposed deficiency.
What it is not: A notice of deficiency is not a bill and not an assessment. It is a notice that the IRS proposes to assess a deficiency, and it gives the taxpayer the right to contest the proposed deficiency in the Tax Court BEFORE paying the tax.
Why it matters: Under IRC 6213(a) (hedge: verify at IRS.gov and in current IRC text), the notice of deficiency is the exclusive gateway to Tax Court jurisdiction over a deficiency. A taxpayer who does not receive (or disputes) a notice of deficiency cannot petition the Tax Court on a deficiency issue. A taxpayer who receives a notice but misses the petition deadline loses the right to contest the deficiency in Tax Court before paying. These are among the most consequential deadlines in tax procedure.
OBBBA context: OBBBA (Pub. L. 119-21, July 4, 2025) made no direct amendments to IRC 6212 or IRC 6213. All notice-of-deficiency mechanics remain under pre-OBBBA statutory law as of the date of this guide. However, as the IRS concludes examinations of OBBBA-era returns -- including Schedule 1A above-the-line deductions, NCTI elections, IRC 530A Trump Accounts, and new charitable deduction structures -- OBBBA-related deficiencies will begin generating notices of deficiency in 2026 through 2029. Practitioners advising clients on OBBBA-era returns should ensure those clients understand these mechanics now. Verify all current law at IRS.gov.
1.1 The Notice as the Trigger for Tax Court Jurisdiction
The Tax Court's jurisdiction over a deficiency case is conditioned on the issuance of a valid notice of deficiency. Without a valid notice, the Tax Court lacks jurisdiction and must dismiss the case (hedge to current case law and IRS.gov; verify the current jurisdictional requirements for Tax Court deficiency petitions at IRS.gov and ustaxcourt.gov). This makes the notice of deficiency, and the timing of its issuance, among the most practically significant documents in any IRS examination.
1.2 Pre-Payment Contest vs. Refund Litigation
The notice of deficiency creates the ONLY statutory path for a taxpayer to contest a federal income tax deficiency in a specialized tax court without first paying the tax. If the taxpayer does not petition the Tax Court within the statutory period after receiving the notice, the IRS may assess the deficiency. The taxpayer can then pay and pursue a refund claim in the U.S. District Court or the U.S. Court of Federal Claims -- but this requires full payment first, a refund claim, and a separate lawsuit (hedge all to current law and IRS.gov). The pre-payment Tax Court path available through a timely notice of deficiency is procedurally and economically distinct from the pay-and-sue refund litigation path.
1.3 The Two Statutes: IRC 6212 and IRC 6213
The notice-of-deficiency framework rests on two statutes (hedge both to their current text at IRS.gov):
- IRC 6212 governs the IRS's authority and obligation to issue the notice: who must receive it, what it must contain, and the address rules for mailing.
- IRC 6213 governs the taxpayer's rights and deadlines after the notice is issued: the petition window, the prohibited-assessment period, the exceptions to that prohibition, the waiver mechanism, and the connection to the assessment SOL.
2. IRC 6212: The IRS's Authority and Obligation to Issue the Notice
2.1 The Mandatory Pre-Assessment Notice
Under IRC 6212 (hedge: verify at IRS.gov and in current IRC text), the IRS is authorized -- and in most deficiency situations required -- to send the taxpayer a written notice before making an assessment of a deficiency. This pre-assessment requirement is the taxpayer's primary procedural protection against surprise assessments. Without issuing the notice, the IRS generally cannot lawfully assess the deficiency (subject to the IRC 6213(b) exceptions discussed in Section 6). Verify the current scope of this requirement and its exceptions at IRS.gov.
2.2 What the Notice Must State
Under IRC 6212 and current IRS practice (hedge to IRS.gov and current IRM; verify at IRS.gov), the notice of deficiency must identify: (a) the tax year or years at issue; (b) the amount of the proposed deficiency for each year; and (c) the basis for the proposed adjustment. In practice, the notice is accompanied by a Revenue Agent Report (RAR) or examination report that sets out the IRS's specific adjustments in detail. Practitioners should review both the notice itself and the accompanying computation for accuracy: errors in the stated deficiency amount or the tax years covered may be relevant to the taxpayer's response.
2.3 Joint Filers and Spousal Notices
For a joint return, IRC 6212 (hedge: verify at IRS.gov and in current IRC text) requires the IRS to send a notice to each spouse separately if they may be separately liable. Sending the notice only to one spouse may affect the other spouse's petition rights or the validity of the notice as to the spouse not addressed. If a practitioner is representing a joint filer where the spouses are separated, divorced, or living at different addresses, confirm that both spouses received the notice and that the petition deadline is calendared for each. Verify current procedures for joint-return notices at IRS.gov.
2.4 What a Notice of Deficiency Is NOT
Practitioners should distinguish the notice of deficiency from other IRS letters to avoid confusion in client communications. The following are NOT notices of deficiency (verify the current description and effect of each notice type at IRS.gov):
- CP2000 notice: Proposes adjustments based on information reporting mismatches. It is a pre-audit inquiry, not a notice of deficiency. Responding to a CP2000 does not restart or waive any petition period.
- 30-day letter (Letter 525/Letter 531): Offers the taxpayer the chance to protest to the IRS Office of Appeals before a notice of deficiency is issued. Receiving a 30-day letter does not start any petition deadline.
- Notice and Demand for Payment (CP14): Issued after assessment. A CP14 notice means the IRS has already assessed the deficiency -- the petition window has either closed or was bypassed.
- Final Notice of Intent to Levy (CP90/CDP Notice): Triggers Collection Due Process rights under IRC 6320/6330. Governed by a separate statutory framework from the notice of deficiency.
3. IRC 6213: The 90-Day and 150-Day Petition Deadlines
Warning: The 90-Day Petition Deadline Has Historically Been Treated as Jurisdictional -- Missing It Eliminates Tax Court as a Pre-Payment Forum
Under IRC 6213(a) (hedge: verify at IRS.gov and in current IRC text), the deadline to petition the Tax Court is 90 days (or 150 days for taxpayers outside the United States) from the date the notice of deficiency is mailed. Courts have historically treated this deadline as jurisdictional, meaning the Tax Court has no power to hear the case if the petition is filed late -- regardless of the reason for the delay. After Boechler v. Commissioner, 142 S. Ct. 1493 (2022) (which addressed a Collection Due Process filing deadline, not the deficiency petition deadline), the Supreme Court and circuit courts have revisited the jurisdictional characterization of several Tax Court filing deadlines. Verify whether any 2025-2026 Supreme Court or circuit authority has altered the jurisdictional treatment of the deficiency petition deadline at IRS.gov and through current legal research. Whether jurisdictional or not, missing the deadline eliminates the Tax Court pre-payment path. The taxpayer's only remaining option is to pay the full deficiency, file a refund claim under IRC 6511, and sue in District Court or the Court of Federal Claims. Calendar this deadline the day the notice arrives -- not the day the mail is opened, reviewed, or forwarded.
3.1 The Domestic 90-Day Rule
Under IRC 6213(a) (hedge: verify at IRS.gov and in current IRC text), a taxpayer whose address is in the United States has 90 days from the date the notice of deficiency is mailed to file a petition with the Tax Court. The petition must be received by the Tax Court (or filed electronically through the DAWSON system) on or before the 90th day. Verify current Tax Court filing procedures, electronic filing availability, and receipt vs. postmark rules at ustaxcourt.gov before advising any client on how to file.
3.2 The 150-Day Rule for Taxpayers Outside the United States
Under IRC 6213(a) (hedge: verify at IRS.gov and in current IRC text), if a taxpayer's address is outside the United States when the notice is mailed, the petition deadline extends to 150 days from the mailing date. Practitioners advising clients who live or work abroad, or who were outside the United States during the period when the notice was mailed, should verify whether the 150-day rule applies to their specific client's facts. Verify the current definition of "outside the United States" for IRC 6213(a) purposes at IRS.gov.
3.3 The Deadline Runs from the Mailing Date -- Not the Receipt Date
The 90-day (or 150-day) period begins on the date the notice is MAILED by the IRS, not the date the taxpayer receives it. This distinction is critical when the notice takes several days to arrive, when the client delays opening mail, or when mail is forwarded to a new address. Practitioners should identify the mailing date from the face of the notice (the date printed at the top) and calendar the petition deadline from that date -- not from the date the client called the office or the date the practitioner received a copy. Any date calculations based on specific mailing dates must be verified independently and labeled "Illustrative Only" in client materials.
3.4 No Extensions by Agreement
The petition deadline cannot be extended by agreement with the IRS, by requesting additional time from the examining agent, or by correspondence with the IRS. The only way to preserve Tax Court jurisdiction is a timely petition. Practitioners should never allow a client to "wait and see" after receiving a notice of deficiency, and should never assume an IRS contact extended or tolled the deadline. Verify current Tax Court jurisdictional requirements at IRS.gov and ustaxcourt.gov.
4. The Last-Known-Address Rule: When the IRS Sends to the Wrong Address
Caution: Clients Who Have Moved Must Update Their Address with the IRS -- A Notice Sent to an Old Address Is Still Valid
Under Treas. Reg. 301.6212-2 (hedge: verify whether this regulation has been revised or superseded at IRS.gov and in the current CFR) and applicable IRS guidance (verify Rev. Proc. 2010-16 or any superseding guidance at IRS.gov), the IRS satisfies its obligation to send the notice of deficiency if it mails the notice to the taxpayer's "last known address" -- which is generally the address shown on the taxpayer's most recently filed return, unless the IRS has received clear and concise written notification of a change of address. A taxpayer who has moved but has not filed a return at the new address and has not submitted a Form 8822 (Change of Address -- verify current version at IRS.gov) may receive a valid notice at the old address. The 90-day clock begins from the mailing date regardless of whether the taxpayer actually received the notice. Advise clients who are under examination, or who have recently moved, to file Form 8822 immediately to update their address with the IRS. For businesses, Form 8822-B is the applicable form (verify current form numbers and requirements at IRS.gov).
4.1 What "Last Known Address" Means
Under Treas. Reg. 301.6212-2 (hedge: verify current regulation text at IRS.gov and in the current CFR), the last known address is the address shown on the taxpayer's most recently filed federal income tax return, unless the IRS has received clear and concise written notification of a different current address. Processing delays at the IRS can mean the agency is not immediately aware of an address change even after a return with a new address is filed. Practitioners should not assume that filing a return with a new address guarantees the IRS has updated its records before issuing a notice. Verify current address-update processing standards at IRS.gov.
4.2 The "Clear and Concise Notification" Requirement
An address change is effective for purposes of the last-known-address rule only if the taxpayer has given the IRS clear and concise written notification of the new address (hedge to Treas. Reg. 301.6212-2 and IRS.gov; verify current requirements). Simply informing an IRS examiner verbally, or mentioning a new address in a letter about an unrelated matter, may not constitute the required clear and concise notification. Form 8822 (Change of Address) is the IRS's designated mechanism for this purpose. Verify current Form 8822 requirements and processing times at IRS.gov before advising any client on how to update their address.
4.3 When the IRS Mails to the Wrong Address
If the IRS sends a notice of deficiency to an address that was NOT the taxpayer's last known address at the time of mailing -- for example, if the IRS uses a stale address in its system that does not reflect the taxpayer's most recently filed return or a Form 8822 previously submitted -- the notice may be invalid. An invalid notice may mean the IRS's assessment is premature and the assessment SOL has not begun running on a new period. These situations are fact-intensive and litigated; the Mulvania line of cases (hedge to current case citations and circuit authority; verify current case law at IRS.gov and through current legal research) and related Tax Court decisions address circumstances under which a mismailing defeats notice validity. Verify current case law on invalid notices at IRS.gov before advising a client who has received a notice at a potentially incorrect address or who claims the IRS used the wrong address.
5. The Prohibited-Assessment Period: What the IRS Cannot Do During the 90 Days
5.1 The Statutory Bar on Assessment
Under IRC 6213(a) (hedge: verify at IRS.gov and in current IRC text), during the 90-day (or 150-day) period following the mailing of a notice of deficiency, the IRS is prohibited from assessing the proposed deficiency and from attempting to collect it. This prohibition is not discretionary -- the IRS may not assess during this period regardless of its belief in the merits of its position. The prohibition gives the taxpayer a meaningful window to evaluate the notice, consult with a practitioner, and decide whether to petition the Tax Court.
5.2 Extension of the Prohibition During Tax Court Proceedings
If the taxpayer timely files a Tax Court petition, the prohibition on assessment extends beyond the initial 90-day period. Under IRC 6213(a) (hedge: verify at IRS.gov and in current IRC text), the IRS is prohibited from assessing the deficiency until the Tax Court's decision becomes final and the assessment period set out in IRC 6213(c) has passed. This means the IRS cannot assess while the Tax Court case is actively litigated, during the appeal period after a Tax Court decision, and during any circuit court appeal of that decision. Verify the current mechanics of when a Tax Court decision becomes final and when the post-decision assessment period runs at IRS.gov and ustaxcourt.gov.
5.3 What the Prohibition Does Not Prevent
The prohibited-assessment period does not prevent the IRS from: (a) continuing the examination of other years or other issues not covered by the notice; (b) seeking extensions of the normal assessment SOL for years for which no notice has yet been issued (through Form 872 consent agreements; hedge to current IRS procedures and IRS.gov); (c) maintaining collection activity against other unpaid liabilities not subject to the notice; or (d) pursuing jeopardy assessment or jeopardy collection actions where applicable (hedge to IRC 6213(b) and current law; see Section 6). Verify current IRS examination and collection procedures at IRS.gov.
6. Exceptions: When the IRS Can Assess Without a Notice of Deficiency
Warning: Do Not Assume That Assessment Without a Notice Means the IRS Acted Improperly -- Verify Whether a IRC 6213(b) Exception Applies
IRC 6213(b) (hedge: verify at IRS.gov and in current IRC text) contains a list of circumstances in which the IRS may assess without first issuing a notice of deficiency. This list is NOT exhaustive; additional statutory exceptions may exist. Before advising a client that the IRS's assessment was improper because no notice of deficiency was issued, verify whether any IRC 6213(b) exception -- or any other statutory authority -- authorized the assessment. An incorrect assumption that the assessment was invalid can lead a client to take the wrong procedural path. Verify all current IRC 6213(b) exceptions and any additional statutory assessment authority at IRS.gov before advising any client.
6.1 Mathematical or Clerical Error Assessments
Under IRC 6213(b)(1) (hedge: verify at IRS.gov and in current IRC text), the IRS may assess additional tax resulting from a mathematical or clerical error on the return without issuing a notice of deficiency. The taxpayer receives a notice of the math-error assessment and has a limited period to request that the IRS abate the assessment and issue a notice of deficiency instead (hedge the request period to current IRC 6213(b)(2) and IRS.gov; verify the current abatement request period and procedures at IRS.gov). Practitioners should identify math-error assessments early because the request for abatement (and the resulting right to a notice of deficiency) may be time-limited. Verify current math-error assessment procedures at IRS.gov.
6.2 Self-Assessed Amounts and Closing Agreements
Under IRC 6213(b) (hedge: verify at IRS.gov and in current IRC text), the IRS may also assess amounts the taxpayer has reported on the return (self-assessed amounts) and amounts the taxpayer has agreed to in a formal closing agreement without the need for a notice of deficiency. A taxpayer who has signed a closing agreement with the IRS has typically waived the right to contest the agreed amounts in Tax Court. Verify the current types of agreements and consents that permit assessment without a notice of deficiency at IRS.gov.
6.3 Jeopardy Assessments
Under IRC 6861 and related provisions (hedge to current IRC text and IRS.gov), the IRS has authority in certain limited situations to make a jeopardy assessment immediately -- without waiting for the prohibited-assessment period to run -- when it determines there is a risk that the assessment or collection will be jeopardized by delay. Jeopardy assessments are subject to judicial review procedures under IRC 7429 (hedge to current IRC text and IRS.gov). Verify current jeopardy assessment authority, requirements, and review procedures at IRS.gov.
6.4 The Non-Exhaustive Character of IRC 6213(b)
Practitioners should treat IRC 6213(b) as a non-exhaustive list of exceptions. Congress has, over time, created additional assessment authorization mechanisms outside of IRC 6213(b). Before concluding that the IRS was required to issue a notice of deficiency before a particular assessment, practitioners should review the full current text of the Internal Revenue Code and applicable Treasury regulations. Verify all current exceptions to the notice-of-deficiency requirement at IRS.gov.
7. Waiver of Restrictions: Form 870 and Strategic Considerations
Caution: Signing Form 870 Waives the Right to Contest the Assessment in Tax Court Without Paying -- Advise Clients Fully Before Signing
Form 870 (Waiver of Restrictions on Assessment and Collection of Deficiency in Tax and Acceptance of Overassessment) allows the taxpayer to consent to the IRS's assessment of the proposed deficiency without requiring the IRS to wait for the 90-day period to expire and without requiring the taxpayer to petition Tax Court. Once filed, the waiver is irrevocable under IRC 6213(d) (hedge: verify at IRS.gov and in current IRC text). Practitioners must advise clients that signing Form 870: (a) ends the prohibited-assessment period immediately; (b) allows the IRS to assess and collect the deficiency; and (c) eliminates Tax Court as a pre-payment contest forum for the amounts covered by the waiver. A client who has strong grounds to contest the IRS's position should not sign Form 870 without fully understanding these consequences. Verify current Form 870 procedures, the irrevocability rule, and whether any limited relief mechanisms exist at IRS.gov.
7.1 What Form 870 Does and Does Not Do
Signing Form 870 (hedge: verify current form name, number, and instructions at IRS.gov) ends the prohibited-assessment period and allows the IRS to assess the deficiency and begin collection. However, signing Form 870 does NOT constitute a closing agreement under IRC 7121, does NOT bar the IRS from asserting additional deficiencies for the same years at a later date, and does NOT prevent the taxpayer from paying the assessed amount and filing a refund claim under IRC 6511 to contest the amount in a refund forum (District Court or the Court of Federal Claims). Verify the current legal effect of Form 870 vs. a closing agreement at IRS.gov.
7.2 Form 870-AD: The Distinction at Appeals
Form 870-AD (Offer to Waive Restrictions on Assessment and Collection of Tax Deficiency) is used at the IRS Office of Appeals and has a materially different legal effect from Form 870. Form 870-AD is generally treated as a formal resolution that precludes the IRS from reopening the case on the same issues absent fraud or concealment, and similarly precludes the taxpayer from contesting the same amounts in a refund forum (hedge: verify the current legal effect of Form 870-AD, its interaction with Tax Court jurisdiction, and any exceptions at IRS.gov and in current Appeals procedures). Practitioners must understand which form is being offered before advising a client to sign. Verify the current distinction between Form 870 and Form 870-AD at IRS.gov.
7.3 Strategic Considerations: When Waiver May Be Appropriate
Signing Form 870 may be strategically appropriate when: (a) the taxpayer agrees with the IRS's proposed deficiency and wants to stop interest from accruing without waiting for the petition period to expire; (b) the taxpayer has decided not to petition Tax Court and wants to resolve the case promptly; or (c) the proposed deficiency is small and the cost of Tax Court proceedings outweighs the benefit of contesting. Signing Form 870 is generally NOT appropriate when: (a) the taxpayer has viable grounds to contest the deficiency; (b) the taxpayer wants to preserve the option to litigate in Tax Court without first paying; or (c) the practitioner has not yet had adequate time to evaluate the IRS's position. Verify all strategic considerations and the current Form 870 procedures at IRS.gov before advising any client.
8. SOL Tolling: How the Notice of Deficiency Suspends the Assessment SOL
8.1 The IRC 6503(a) Tolling Mechanism
Under IRC 6503(a) (hedge: verify at IRS.gov and in current IRC text), the normal three-year (or six-year, or unlimited) assessment period under IRC 6501 is suspended from the date the notice of deficiency is mailed until the date the Tax Court decision becomes final, plus an additional 60-day period. This tolling is automatic -- the taxpayer does not need to take any action to trigger it, and the IRS does not need to seek a court order. Verify the current mechanics of IRC 6503(a) tolling and the post-decision 60-day period at IRS.gov.
8.2 Why Tolling Matters: The Prohibited-Assessment Period Creates a Timing Gap
The interaction between the prohibited-assessment period (IRC 6213(a)) and the SOL tolling provision (IRC 6503(a)) is practically important. During the prohibited-assessment period, the IRS cannot assess even though the deficiency has been proposed. Without tolling, a lengthy Tax Court proceeding could allow the normal assessment SOL to expire while the IRS was prohibited from acting. IRC 6503(a) solves this problem by stopping the SOL clock for the duration of the prohibited-assessment period and the Tax Court proceedings. The practical effect is that the IRS retains the ability to assess the deficiency after the Tax Court case concludes, even if the normal IRC 6501 period would have expired in the interim (any specific date example labeled "Illustrative Only"). Verify current tolling mechanics at IRS.gov.
8.3 Cross-Reference: The IRC 6501 SOL Framework
The IRC 6503(a) tolling provision operates against the baseline IRC 6501 assessment SOL. The standard three-year assessment period, the six-year substantial-understatement exception, and the unlimited-assessment exception for fraud all establish the starting clock that IRC 6503(a) tolls. Practitioners handling a deficiency case involving a notice of deficiency should maintain a SOL calendar that tracks both the baseline IRC 6501 period and any applicable tolling under IRC 6503(a). See the IRC 6501 Audit Statute of Limitations guide in the Related Guides section for the base SOL rules. Verify all SOL periods and tolling provisions at IRS.gov and in the current IRC before advising any client.
8.4 Tolling When No Petition Is Filed
The IRC 6503(a) tolling applies regardless of whether the taxpayer petitions the Tax Court. Even if the taxpayer does not petition, the mailing of the notice of deficiency suspends the assessment SOL during the 90-day period (and for 60 days thereafter). After the 90-day period expires without a petition, the IRS may assess and the SOL resumes. Verify current tolling mechanics for the no-petition scenario at IRS.gov.
9. After the 90 Days: What Happens If No Petition Is Filed
9.1 The IRS Assesses the Deficiency
If the 90-day (or 150-day) period expires without the taxpayer filing a Tax Court petition, the IRS may proceed to assess the full deficiency and any applicable interest and penalties. After assessment, the IRS will typically send a notice and demand for payment (often a CP14 notice or similar). If the taxpayer does not pay promptly, the IRS may proceed to collection through liens, levies, and other enforcement mechanisms. The collection process is governed by a separate set of procedural protections (Collection Due Process, installment agreements, offers in compromise) that fall outside the scope of this guide. Verify current post-assessment collection procedures at IRS.gov.
9.2 The Refund Litigation Path
After the IRS assesses the deficiency and the taxpayer fails to petition Tax Court, the taxpayer's remaining path to contest the deficiency on the merits is the refund litigation route: (1) pay the assessed deficiency in full (or the portion the taxpayer disputes); (2) file a refund claim under IRC 6511 within the applicable limitation period; (3) wait for the IRS to deny the claim or for the claim to be deemed denied by inaction; and then (4) file a refund suit in the U.S. District Court for the district where the taxpayer resides or the U.S. Court of Federal Claims (hedge all steps to current law and IRS.gov). Verify current refund claim procedures, the "full payment" rule in District Court deficiency cases, and the applicable limitations periods at IRS.gov and in the IRC 6511 guide in the Related Guides section.
9.3 Timing of the Election: The 90-Day Period as a Decision Window
The 90-day period after receiving a notice of deficiency functions as an important strategic decision window. Practitioners should use this time to: (a) thoroughly evaluate the IRS's position on the merits; (b) gather any additional documentation that may support the taxpayer's case; (c) consult with any experts needed to assess the technical or valuation issues in the notice; (d) obtain a written assessment of the taxpayer's litigation position; and (e) advise the client on the costs, timeline, and realistic outcomes of Tax Court proceedings compared to paying and filing a refund claim. All of this analysis should be complete before the petition deadline -- not after. See the Tax Court Petition guide in the Related Guides section for the mechanics of filing the petition itself.
10. Practical Workflow: Receiving the Notice, Calendaring the Deadline, and Client Communication
10.1 Immediate Steps on Receipt
The following steps should be taken immediately upon a practitioner's or client's receipt of a notice of deficiency (hedge all procedural specifics to current IRS.gov and ustaxcourt.gov; procedures can change):
- Identify and calendar the mailing date. The mailing date appears at the top of the notice. Calendar the 90-day petition deadline immediately, treating it as a hard deadline with no exceptions. If the taxpayer may be "outside the United States" within the meaning of IRC 6213(a), verify whether the 150-day rule applies at IRS.gov.
- Verify the address used. Confirm that the address on the notice matches the address on the taxpayer's most recently filed return. If it does not, investigate whether the notice is valid (Section 4). If the taxpayer has recently moved and has not submitted Form 8822, do so immediately -- but understand that this does not retroactively extend the current petition period.
- Identify all years and issues covered. A single notice may cover multiple tax years. Each year's deficiency is independently subject to the petition deadline. Identify all years and all proposed adjustments in the accompanying Revenue Agent Report.
- Assess the merits. Review the RAR or examination report accompanying the notice. Identify which proposed adjustments are defensible, which are questionable, and which the taxpayer accepts. Determine what additional information or documentation would be needed for a Tax Court proceeding.
- Advise the client promptly. Contact the client immediately and explain: (a) what the notice is; (b) that the 90-day clock is running from the mailing date; (c) the three options (petition Tax Court, sign Form 870 and waive, or do nothing and allow assessment); and (d) the recommendation. Verify all current procedural requirements at IRS.gov.
10.2 Forum Selection: Tax Court vs. Refund Courts
The 90-day window is the critical decision point for forum selection. Use the following framework to guide the analysis (hedge all forum-selection considerations to current law and IRS.gov; the choice of forum is a substantive strategic decision that requires analysis of the client's specific facts):
| Forum | When available | Payment required first? | Key considerations (illustrative; verify at IRS.gov) |
|---|---|---|---|
| U.S. Tax Court | Timely petition within 90 days (or 150 days) of notice of deficiency mailing date | No -- this is the pre-payment forum | Specialized tax judges; no jury; must petition within the statutory window; S-case election available for smaller amounts (verify current threshold at IRC 7463 and ustaxcourt.gov) |
| U.S. District Court | After full payment of the deficiency and denial (or deemed denial) of a refund claim | Yes -- full payment required | Jury trial available; general federal court; requires payment and separate refund litigation; governed by 28 U.S.C. section 1346 (hedge; verify at IRS.gov) |
| U.S. Court of Federal Claims | After full payment and denial (or deemed denial) of refund claim | Yes -- full payment required | Specialized federal court; no jury; requires payment and refund litigation; typically more complex and expensive for smaller cases (hedge; verify at IRS.gov) |
| IRS Office of Appeals (before petition) | If taxpayer has not yet received notice of deficiency and received a 30-day letter | No | Administrative settlement; does not require a petition; settlement at Appeals typically stops notice of deficiency from being issued; available only before the notice is issued (verify at IRS.gov) |
10.3 Client Communication Priorities
Practitioners should communicate the following to every client who receives a notice of deficiency (hedge all specifics to current law and IRS.gov):
- The 90-day deadline is absolute. There is no extension, grace period, or forgiveness for missing it (note: verify any post-2025 case law developments on this point at IRS.gov).
- The practitioner -- not the client -- will track the deadline. The client should not rely on any "respond by" date printed on the notice without confirming the mailing date independently.
- The decision to petition Tax Court or waive is the client's to make after informed counseling from the practitioner. The practitioner should provide a written recommendation with the relevant legal analysis before the client decides.
- If the client is considering signing Form 870, they must understand that it ends Tax Court jurisdiction and allows immediate assessment. See Section 7.
11. Connection to Tax Court Petition: From Notice to Petition in 90 Days
Warning: The Tax Court Petition Window Cannot Be Extended -- Only a Timely Filed Petition Preserves Tax Court Jurisdiction
The Tax Court petition window cannot be extended by: an agreement with the IRS to "hold off" on collection; a letter to the examining agent requesting more time; a conversation with Appeals; or any other informal arrangement. If the taxpayer asks the IRS for an extension and the IRS agrees informally, that agreement has no legal effect on the petition deadline. The only action that preserves Tax Court jurisdiction is a petition filed with the Tax Court on or before the 90th day (or 150th day) after the mailing date of the notice of deficiency. Verify current Tax Court filing procedures at ustaxcourt.gov. Calendar this deadline immediately and confirm it in writing with the client.
11.1 Filing the Tax Court Petition
The Tax Court petition must be filed through the Tax Court's DAWSON electronic filing system (Docket Access Within a Secure Online Network) or by mailing to the Tax Court (hedge all mechanics to current ustaxcourt.gov procedures; filing procedures can change). The petition must identify: (a) the petitioner's name and address; (b) the tax year or years at issue; (c) the amount of the deficiency in dispute; and (d) the specific errors the petitioner alleges in the IRS's determination. Practitioners should review the Tax Court's current petition requirements, fee schedules, and filing procedures at ustaxcourt.gov before advising any client on how to file. See the Tax Court Petition guide in the Related Guides section for the full petition procedure.
11.2 The S-Case Election Under IRC 7463
For cases meeting the applicable threshold under IRC 7463 (hedge: do NOT state a specific dollar amount; verify the current S-case threshold at current IRC 7463 and ustaxcourt.gov), the taxpayer may elect to have the case heard under the Tax Court's simplified procedures for small tax cases (S-cases). S-case decisions are not precedential and cannot be appealed by either party. S-cases are generally faster and less expensive than regular Tax Court proceedings and may be appropriate when the deficiency amount is small and the factual issues are straightforward. Verify the current S-case eligibility threshold, the election procedure, and whether S-case treatment is appropriate for the client's facts at ustaxcourt.gov.
11.3 Coordination with IRS Examination and Appeals
In some situations, a taxpayer who receives a notice of deficiency after bypassing Appeals (or where Appeals conferences were unavailable) may wish to pursue Appeals settlement even after a petition is filed. The Tax Court's jurisdiction does not automatically prevent Appeals involvement; the IRS has procedures under which a Tax Court case can be placed on hold for settlement discussions at Appeals (hedge: verify current Tax Court/Appeals coordination procedures at IRS.gov and ustaxcourt.gov). Verify whether this option is available and appropriate for the client's facts before filing a petition solely to "stop the clock" while expecting settlement.
12. Practitioner Checklist
Use this checklist for every client who receives a notice of deficiency. All items hedged to current IRC text and IRS.gov; verify before advising any client.
- On the day of receipt: calendar the mailing date from the face of the notice and calculate the petition deadline. The petition deadline runs from the mailing date, not the receipt date. If the taxpayer's address is "outside the United States" within the meaning of IRC 6213(a), verify whether the 150-day rule applies. Record the deadline in the client file and in the firm's docket system. Verify the current 90-day and 150-day rule at IRS.gov.
- Confirm the petition deadline is calendared for each tax year covered by the notice. A single notice may cover multiple years. Each year's proposed deficiency is included in the same petition deadline, but practitioners should confirm all years and all adjustment items are documented. Verify current Tax Court procedures for multi-year petitions at ustaxcourt.gov.
- Verify that the address on the notice was the taxpayer's last known address as of the mailing date. If the taxpayer had moved and not submitted Form 8822 or filed a return at the new address, assess whether the notice is valid. If the notice was sent to a clearly wrong address, investigate whether the notice can be challenged. Verify current last-known-address rules and case law at IRS.gov.
- If the client has recently moved, file Form 8822 (or Form 8822-B for businesses) immediately. This does not retroactively extend the current petition deadline, but it updates IRS records to prevent a future notice from going to the wrong address. Verify current Form 8822 requirements and processing times at IRS.gov.
- Evaluate the IRS's position on the merits and assess the litigation risk before the 90-day window closes. Determine which proposed adjustments are defensible, which are questionable, and which the taxpayer accepts. Obtain expert opinions or additional documentation as needed before the deadline -- not after. Verify current Tax Court procedural requirements at ustaxcourt.gov.
- Advise the client on all three options: petition Tax Court, sign Form 870 and waive, or do nothing and allow assessment after 90 days. Explain the consequences of each option in writing before the client decides. Never allow a client to sign Form 870 without understanding that it ends Tax Court jurisdiction and allows immediate assessment. Verify current Form 870 procedures and their legal effect at IRS.gov.
- If petitioning Tax Court: identify all years and issues to include in the petition. Verify whether the S-case election under IRC 7463 is available and appropriate for the client's deficiency amount and factual complexity. File the petition through DAWSON on or before the 90th day. Verify current petition requirements and the S-case threshold at ustaxcourt.gov.
- Verify whether any IRC 6213(b) exception might apply before concluding a notice of deficiency was required. If the IRS has already assessed without issuing a notice, confirm whether a math-error, self-assessment, closing-agreement, or other IRC 6213(b) exception authorized the assessment before advising the client that the assessment was improper. Verify current IRC 6213(b) exceptions at IRS.gov.
- Note the IRC 6503(a) SOL tolling in the client file. The assessment SOL is suspended from the mailing date of the notice through the final Tax Court decision plus 60 days. Update the SOL calendar to reflect the suspension period. Verify current IRC 6503(a) tolling mechanics at IRS.gov.
- If the client will not petition Tax Court, plan the refund litigation strategy before assessment occurs. After assessment and collection, the client must pay, file a refund claim under IRC 6511 within the applicable period, and then file a refund suit in District Court or the Court of Federal Claims if the claim is denied. Map out this timeline before the 90-day window closes. Verify current refund claim procedures and limitation periods at IRS.gov and in the IRC 6511 guide in the Related Guides section.
13. Claims Notice
Regulated Claims, Required Verifications, and Limitations
This guide contains statements about the notice of deficiency mechanics under IRC 6212 and IRC 6213, including the petition deadline, the last-known-address rule, the prohibited-assessment period, and the IRC 6503 SOL tolling provision. All statements reflect publicly available sources as of July 2026 and are subject to change through legislative amendment, regulatory revision, or judicial decisions. The following claims require independent verification before use in any client engagement.
| Claim or Statement | Standard | Primary Authority | Required Verification |
|---|---|---|---|
| The 90-day petition deadline: domestic taxpayers have 90 days from the notice mailing date to petition Tax Court | Statutory deadline; historically treated as jurisdictional by courts; post-Boechler case law continues to develop | IRC 6213(a); IRS.gov; current Tax Court and circuit case law | Verify the current 90-day rule and whether any 2025-2026 Supreme Court or circuit decisions altered the jurisdictional characterization of the deficiency petition deadline at IRS.gov and through current legal research |
| The 150-day rule for taxpayers "outside the United States" | Statutory extension; applies to taxpayers whose address is outside the United States when the notice is mailed | IRC 6213(a); IRS.gov | Verify the current definition of "outside the United States" for IRC 6213(a) purposes and the 150-day rule's application to specific fact patterns at IRS.gov before advising any client |
| The last-known-address rule: a notice sent to the last known address is valid even if not received | Regulatory and judicial standard; "last known address" is the address on the most recently filed return unless clear and concise written notification of change was given | Treas. Reg. 301.6212-2; Rev. Proc. 2010-16 (verify whether superseded); IRS.gov | Verify current last-known-address regulation text and whether Rev. Proc. 2010-16 has been superseded or updated at IRS.gov before advising any client who disputes the validity of a notice on address grounds |
| The prohibited-assessment period: the IRS cannot assess during the 90-day window | Statutory prohibition; mandatory; extends during Tax Court proceedings | IRC 6213(a); IRS.gov | Verify the current scope of the prohibited-assessment period and when it ends (including the post-Tax-Court-decision period) at IRS.gov |
| IRC 6213(b) exceptions: assessment is permitted without a notice of deficiency in certain situations | Statutory exceptions; list is NOT exhaustive; additional exceptions may exist | IRC 6213(b); IRS.gov | Verify all current IRC 6213(b) exceptions and any additional statutory assessment authority before advising any client that the IRS was required to issue a notice of deficiency for a particular assessment |
| Form 870 waiver: signing waives Tax Court pre-payment contest and is irrevocable under IRC 6213(d) | Statutory rule; Form 870 waiver is irrevocable once filed; distinction from Form 870-AD (Appeals settlement) | IRC 6213(d); current IRS Form 870 instructions; IRS.gov | Verify current Form 870 and Form 870-AD procedures, the irrevocability rule, and the legal distinction between a waiver and a closing agreement at IRS.gov before advising any client to sign either form |
| IRC 6503(a) SOL tolling: the assessment SOL is suspended from notice mailing through final Tax Court decision plus 60 days | Statutory tolling; automatic; applies whether or not the taxpayer petitions Tax Court | IRC 6503(a); IRS.gov | Verify the current tolling period, when the 60-day post-decision period runs, and how IRC 6503(a) interacts with the various IRC 6501 assessment periods at IRS.gov |
| The S-case threshold under IRC 7463 | Statutory threshold for Small Tax Case procedures; amount is not stated in this guide as a bare figure | IRC 7463; ustaxcourt.gov | Verify the current S-case eligibility threshold at current IRC 7463 text and ustaxcourt.gov before advising any client on the S-case election |
| Boechler v. Commissioner and its effect on the deficiency petition deadline characterization | Supreme Court decision addressing CDP filing deadline; not directly applicable to deficiency petition deadline; courts continue to apply the Boechler framework to other Tax Court filing deadlines | Boechler v. Commissioner, 142 S. Ct. 1493 (2022); current circuit authority; IRS.gov | Verify the current state of circuit court and Tax Court authority on the jurisdictional vs. non-jurisdictional characterization of the deficiency petition deadline at IRS.gov and through current legal research before advising any client who has missed or may miss the deadline |
Not Legal Advice
This guide is provided for general informational and educational purposes for tax practitioners and does not constitute legal advice, tax advice, or the establishment of a practitioner-client relationship. The information reflects publicly available sources as of July 2026 and may not reflect subsequent changes to the Internal Revenue Code, Treasury regulations, or judicial decisions. America's Tax Professionals makes no representation that the information in this guide is complete, current, or applicable to any specific client's facts. Practitioners are responsible for independently verifying all statements at IRS.gov and through current legal research before advising any client.