TC 171: Estimated Tax Penalty Abated (Manual)

By Forrest Baumhover, CFP®, EA · Last verified August 24, 2026

TC 171 is the code that means an IRS employee manually reduced or removed an estimated tax penalty — and the penalty reason code behind it reveals exactly which of a handful of narrow grounds actually worked.

What the code actually does

TC 171 is a credit transaction — the code an IRS employee enters when a previously posted ES penalty is reduced or removed by hand. IRM 20.1.3.2.1 defines it simply as "Manual abatement of an ES penalty by IRS"; IRS Document 6209’s own table is more specific about scope: "Abates previously posted 170 or 176 Estimated Tax Penalty in whole or in part." A TC 171 does not care whether the penalty it is reducing began as a self-assessed or IRS-assessed TC 170 or a computer-generated TC 176 — that "170 or 176" language is Document 6209’s own, and neither the IRM nor Document 6209 states any required order between the two.

Because this is a manual transaction, it does not post on its own — it requires a penalty reason code "in the fourth reason code position of the ADJ54 adjustment input screen," per IRM 20.1.3.2.2, the Manual Penalty Adjustments subsection covered next. That code is not paperwork; it is the actual record of why the IRS agreed the penalty was wrong, and it is the single most useful thing to look for when reading a transcript that already shows a TC 171 — it tells you which argument already worked, or, read the other way, which arguments remain untried.

The five grounds that actually get this posted

IRM 20.1.3.2.2’s penalty reason code table lists exactly five grounds for a manual abatement, and the exact wording matters because it decides which one applies. PRC 045 exists to correct "any IRS computational error in the ES penalty computation, whether or not the penalty was originally assessed with TC 176 or with TC 170." PRC 016 and PRC 010 both apply only where "the original penalty was self-assessed (TC 170 posted with return)" — 016 for a corrected computation, 010 for a superseding return. PRC 013 is the IRS-assessed mirror of 010: it applies where "the original penalty was IRS assessed (TC 176)," adjusted for a superseding return or a taxpayer-supplied computation.

That leaves one code, PRC 044, as the only ground that reaches the merits rather than the math: it applies where "the taxpayer qualifies for a specific waiver listed in the Form 2210 or Form 2220 instructions," or where the penalty resulted from the taxpayer’s reliance on erroneous written IRS advice. Four of the five available grounds are computational corrections keyed to which code originally assessed the penalty; only one reaches an actual waiver. That ratio is the clearest evidence in the source of how narrow real relief is here — most TC 171s exist because a number was wrong, not because the IRS agreed to forgive a correctly computed penalty.

What doesn’t work, and the two waivers that sometimes do

PRC 044’s "specific waiver" does not mean reasonable cause. IRM 20.1.3.2.7.1 is explicit: "The penalty for underpayment of estimated tax cannot be removed or waived for reasonable cause alone." The two waivers that actually exist for individuals both come from IRC §6654(e)(3): a casualty/disaster/unusual-circumstances equity waiver under (e)(3)(A) — which the IRM specifically distinguishes from reasonable cause, noting that reliance on a tax advisor’s advice does not qualify under this provision even though it can support reasonable-cause relief from other penalties — and a much narrower retirement-or-disability waiver under (e)(3)(B), available only where the taxpayer retired after 62 or became disabled in the underpayment year or the year before, with the underpayment itself due to reasonable cause. Corporations have almost nothing comparable; the ES penalty "generally does not qualify for a waiver, with very specific exceptions," the last of which was legislated for 2001.

A waiver claim must be in writing and signed by the taxpayer — an oral request does not count, per IRM 20.1.3.3.2.1.2, the subsection governing how these §6654(e)(3)(A) claims are evaluated.

What TC 171 gets confused with

TC 171 and TC 177 both reduce an ES penalty, and it is easy to treat them as the same event recorded two different ways. They are not identical in scope. Document 6209 defines TC 171 broadly — it "abates previously posted 170 or 176" — but TC 177 narrowly: it "abates a previously assessed TC 176" only. A manual abatement can reach a self-assessed penalty; the fully computer-generated abatement cannot, because Master File has no way to know whether a self-assessed number on a filed return was ever wrong in the first place without a human looking at it.

The other confusion is with the Failure to File penalty’s own abatement code, TC 161. They look parallel — both are manual abatement codes sitting opposite a manual assessment code — but the relief regimes behind them are not parallel at all. TC 161 abates a penalty that is First-Time Abate eligible and subject to the IRS’s ordinary reasonable-cause standard; TC 171 abates a penalty that is neither. A practitioner who successfully argues reasonable cause or FTA to reverse a TC 160 and then tries the identical argument against a TC 170 will find it does not transfer — the Penalty Abatement Analyzer is built around FTF, FTP, FTD, and accuracy-related penalty relief specifically because those are the penalties reasonable cause and FTA actually reach; it does not model the ES penalty, because the grounds above are the only ones that do.

The practitioner’s actual next step

Match the fact pattern to a PRC before drafting anything. If the penalty was self-assessed and the client’s own Form 2210 math was wrong, that is PRC 016 territory — recompute the number and submit the correction, not a narrative. If a superseding return changed the underlying tax, that is PRC 010 or 013 depending on which code assessed the original penalty. Save the waiver argument under PRC 044 for the cases that actually meet §6654(e)(3)(A) or (e)(3)(B) — casualty, disaster, unusual circumstances weighed against equity and good conscience, or the narrow retirement/disability gate — because a computational request dressed up as a waiver claim, or the reverse, is the fastest way to get the wrong reason code applied.

Put the request in writing and get the taxpayer’s signature on it — IRM 20.1.3.3.2.1.2 is explicit that an oral request does not qualify for a §6654(e)(3)(A) waiver. If it is denied, IRM 20.1.3.2.8 requires the IRS to send an 854C letter — "Penalty Waiver or Abatement Disallowed/Appeals Procedure Explained" — laying out the reason for denial and the appeal rights, with a TC 290 for zero dollars entered on the account to record the denial itself. That appeal runs administratively, to the IRS’s own Independent Office of Appeals, not to Tax Court: IRC §6665(b) excludes the ES penalty from deficiency procedures except where no return was filed, so a denied waiver standing alone is ordinarily pursued through Appeals, or by paying the penalty and suing for a refund. And if none of the five grounds fit and the client simply cannot pay the assessed balance, the right next conversation is about Currently Not Collectible status for the account as a whole — or an Offer in Compromise — not a sixth attempt at an abatement argument the source does not support.