Exceptions (IRC 6404(g)(2))
The 36-month rule
IRC 6404(g)(1)(A) applies to “an individual who files a return of tax imposed by subtitle A for a taxable year on or before the due date for the return (including extensions).” If the IRS “does not provide a notice to the taxpayer specifically stating the taxpayer’s liability and the basis for the liability before the close of the 36-month period beginning on the later of” the date the return is filed or its due date without extensions, it must suspend interest and any time-sensitive penalty allocable to the suspension period. The period was 18 months when the provision was enacted in 1998 and became 36 months under Pub. L. 110-28, which “shall apply to notices provided by the Secretary of the Treasury, or his delegate, after the date which is 6 months after the date of the enactment of this Act,” May 25, 2007, so November 25, 2007. Treas. Reg. 301.6404-4(a)(5) and IRM 20.2.7.8.3 translate that: if the 18-month period had already closed on November 25, 2007 without notice, the suspension began then; otherwise the IRS had 36 months. The calculator makes that choice from the dates, and for any return filed in the last two decades the answer is 36 months. IRM 20.2.7.8 confirms the extension point: “A timely filed return for this purpose includes one filed in accordance with an extension.” A late return gets nothing for that year. The interest abatement guide places the rule among the other IRC 6404 provisions.
How the IRS counts the period
IRM 20.2.7.8.3 starts the clock on the return due date when the return was received by then, on the postmark date when it was filed on the next business day after a weekend or holiday due date, and on the received date when it came in under an extension. It then states that, at Chief Counsel’s suggestion, “the ‘months’ in the 36 (or 18) month notification period is calculated as ‘36 (or 18) months minus 1 day,’” and that if that day is a Saturday, Sunday or legal holiday “the next business day becomes the end date.” The suspension starts the next day (IRC 6404(g)(3)(A)) and ends on “the date which is 21 days after the date on which notice described in paragraph (1)(A) is provided by the Secretary” (IRC 6404(g)(3)(B)); IRM 20.2.7.8.4 adds that “Interest resumes the 22nd day after the 6404(g) notice date.” The calculator follows the IRM counting, which the regulation’s own examples confirm except on the weekend roll: Treas. Reg. 301.6404-4(a)(6), Example 2, has a return filed April 15, 2009 and a notice on December 20, 2012, with suspension from April 15, 2012 through January 10, 2013, while the IRM would move the Saturday, April 14, 2012 close to the next business day. The difference is at most a few days and the IRM is what the campus applies.
The notice must be in writing and “specifically state the amount of the liability and the basis for the liability,” with enough detail to identify the items adjusted and the reason; “Notice of the reason for the adjustment does not require a detailed explanation or a citation to any Internal Revenue Code section or other legal authority” (Treas. Reg. 301.6404-4(a)(7)). An examination report under a 30-day letter, a Form 4549 with Form 886-A, a CP 2000 or a notice of deficiency all qualify; a letter that proposes no amount, such as an appointment letter or an information document request, cannot, because the statute requires both the amount and the basis. The rule runs item by item (IRC 6404(g)(1)(B)): a second report that adds an issue starts a separate notice date for that issue (IRM 20.2.7.8.5.1), and an amended return that reports more tax is both the new start date and the notice for what it reports, so no suspension arises on self-reported amounts received on or after December 21, 2005 (Treas. Reg. 301.6404-4(a)(2)).
What the suspension is worth
The statute suspends “any interest, penalty, addition to tax, or additional amount with respect to any failure relating to the return which is computed by reference to the period of time the failure continues to exist and which is properly allocable to the suspension period.” Interest under IRC 6601 is the main item; the failure-to-pay addition is carved out by IRC 6404(g)(2)(A). The IRM 20.2.7.8.6 routine shows how the suspension is computed: a 1998 return filed April 15, 1999 and a report dated December 1, 2000 produced $536.21 of interest on $4,000 from April 15, 1999 to October 16, 2000 (the 18-month close, a Saturday, moved to Monday), no interest on $4,536.21 from October 17 through December 22, 2000, and interest resuming on $4,536.21 from December 23. The calculator uses the same structure with daily compounding at the quarterly IRC 6621(a)(2) rates (the same table as the interest rate page) and reproduces those IRM figures when the 1999 to 2001 rates are supplied; the published figure it shows is the difference between interest with and without the suspension. It is an estimate: it ignores payments and credits during the period, the IRC 6601(c) suspension after a signed waiver, the large corporate underpayment rate (not relevant to individuals) and penalties.
How the suspension is applied and how to claim it
Examiners record whether IRC 6404(g) applies and the notice date on the closing documents, and the date is posted with TC 971 AC 064 and the eligible amount: “Only input TC 971 AC 064 if notification was not made within the 36 (or 18) month period” (IRM 20.2.7.8.5.3). With one notice date and one tax adjustment Master File computes the suspension systemically; with multiple adjustments the interest must be computed manually or the adjustment unposts (IRM 20.2.7.8.6). On a transcript, a TC 971 AC 064 with a date more than 36 months after the filing date is the sign the IRS recognized the suspension; its absence on a late-noticed year is the sign to ask. The request is Form 843 or signed correspondence with the same elements, identified on the account with TC 971 AC 660 (IRM 20.2.7.14). There is no appeal and no Tax Court review of a 6404(g) determination (IRM 20.2.7.15), unlike an IRC 6404(e) abatement claim under IRC 6404(h); the practical remedy is a corrected computation showing the filing date, the notice date and the suspension period.
Worked example
A 2021 Form 1040 was filed on Monday, April 18, 2022, the due date that year because April 15 was Emancipation Day in the District of Columbia. The 36-month period starts April 18, 2022 and closes 36 months minus one day later, on Thursday, April 17, 2025. The IRS mailed a CP 2000 on July 14, 2025 proposing $10,000 of additional tax, and the taxpayer paid in full on September 30, 2025. The notice came after the close, so interest is suspended from April 18, 2025 through August 4, 2025 (21 days after the notice), 109 days, and resumes August 5. At the 7 percent rate in effect from 2023 through 2025 the interest on $10,000 from April 15, 2022 to April 17, 2025 is $2,325.38 (the 2022 quarters were 4, 5 and 6 percent); the 109 suspended days would have added about $260 on the $12,325.38 balance, and with the interest that amount would itself have earned to the payment date the suspension removes $263.20 of the $398.66 of interest that would otherwise accrue from April 17 to September 30, 2025, leaving $135.46 for the resumed period. Had the CP 2000 been mailed on April 17, 2025 or earlier, nothing would be suspended. The example button loads these facts; the two IRM 20.2.7.8.4 examples (an 18-month case with suspension from October 17, 2000 to September 27, 2001, and an extended-return case received June 19, 2003 with suspension from December 21, 2004 to December 23, 2005) and the regulation example above were used to test the date logic.
Questions practitioners ask
Does the 36 months run from the extended due date?
No. The period begins on the later of the filing date or the due date without regard to extensions (IRC 6404(g)(1)(A)). An extension only preserves eligibility: a return filed within the extension is timely, and the clock starts on the day it was actually filed.
The IRS sent an audit appointment letter within 36 months. Does that stop the suspension?
Not by itself. The notice must state the amount of the liability and its basis (Treas. Reg. 301.6404-4(a)(7)). An appointment letter or an information document request proposes nothing. The first report, 30-day letter, CP 2000 or notice of deficiency that states the adjustment and amount is the notice.
Is interest suspended for a corporation or a partnership adjustment?
The statute covers individuals who file subtitle A returns. IRM 20.2.7.8 says it applies to an individual's liability from a flow-through or TEFRA adjustment, with notice to the partner or TMP tested under Treas. Reg. 301.6404-4(a)(7)(ii). A corporation's own return is outside the rule.
Does the suspension cover the accuracy-related penalty?
Only penalties computed by reference to the period of time the failure continues to exist are suspended. The IRC 6662 penalty is a fixed percentage of the underpayment and is not time-based; the IRC 6651 failure-to-pay addition is time-based but is expressly excluded by IRC 6404(g)(2)(A). Interest is the main benefit.
Does the suspension apply if the taxpayer agreed to extend the assessment statute?
Yes. Treas. Reg. 301.6404-4(a)(6), Example 2, is a taxpayer who signed a consent extending the statute to June 30, 2013; the suspension still ran from the close of the 36-month period until 21 days after the December 2012 notice. A statute extension does not extend the notice period.
What should the transcript show?
A TC 971 with action code 064 dated with the notice date, input only when the notice was late (IRM 20.2.7.8.5.3). If the account shows interest accruing straight through a late-noticed period, a Form 843 or signed letter citing IRC 6404(g) with the filing date, the notice date and the computed period asks the campus to correct it (IRM 20.2.7.14).