TC 309: Examination Overassessment With an Interest Computation Date

What the code actually does

IRS Document 6209, Section 8A describes TC 309 as an "Examination Overassessment of tax to a module which contains a TC 150," carrying Doc Code 47 — the examination and Appeals document code, the same one behind TC 300. Like its Doc Code 54 counterpart, it "contains an interest computation date which must be included in the transaction and generates abatement of interest from that date." The mechanism is identical; only the origin of the abatement changes.

That origin is the whole reason the code exists separately from a plainer exam abatement. An Examination Overassessment is a determination — Appeals or an examiner concluded the tax on the module was too high — and the interest computed on the excess has to unwind from a specific point, not from whatever date the module's running calculation happens to be using.

Form 2285 is the real document behind the code

TC 309 names its real-world source document directly: Form 2285. IRM 8.17.6.4 describes it as "Form 2285, Concurrent Determinations of Deficiencies (sometimes called a Restricted Interest Worksheet)," prepared when a case has more than one adjustment competing for the same tax dollars — typically a general adjustment layered against one or more carryback years. A Tax Computation Specialist builds the form column by column, in a fixed order, so that interest on each adjustment is computed against the correct, narrower base rather than against the return as a whole.

That is the case a TC 309 is built to record. Where an exam produces both an assessment and an overassessment tangled up with a carryback or another restricted-interest adjustment, Form 2285 works out how much of the module's tax is attributable to which adjustment, and the interest computation date on the TC 309 reflects that division rather than a single, simple exam closing date.

The guardrail: it cannot abate more than the module actually has

Doc 6209 attaches a guardrail that is easy to miss: TC 309 "cannot be used if the amount of tax in the module is smaller than the amount on the Form 2285 that could be input" with it. In plain terms, the system will not let an examination overassessment abate more tax than the module actually shows — a data-integrity check against the case running ahead of what actually posted, whether from a timing gap between the exam closing and an earlier adjustment, or from an error in the Form 2285 computation itself.

A TC 309 that fails to post for this reason is not a rejected relief request. It is the module refusing to remove tax that, according to its own records, is not there to remove — which means the real issue lives in an earlier transaction or in the Form 2285 figures, not in whether the overassessment itself was correct.

What TC 309 gets confused with

TC 309 gets confused with TC 291 and TC 299, because all three abate a prior tax assessment and two of the three share the identical interest-computation-date mechanic. The distinction is Doc Code: TC 291 and TC 299 are Doc Code 54, a general adjustment, while TC 309 is Doc Code 47, an examination or Appeals determination. Seeing the interest-date mechanic on a module is not, by itself, evidence that an exam was involved — only the Doc Code answers that question.

It is also mistaken for a plain TC 301, the ordinary examination abatement. The two overlap almost completely — both remove tax an exam or Appeals determination assessed — and the difference is exactly the same one that separates TC 299 from TC 291: TC 309 exists because a mandatory interest computation date, tied to a Form 2285 restricted-interest computation, has to be attached. On the individual side, Doc 6209 adds that TC 309 "cannot be used with other tax transaction codes" at all, a constraint the plainer exam abatement does not carry. A TC 309 sharing a document with an unrelated tax adjustment on an IMF (Individual Master File) module is not how the transaction is meant to post.

Like TC 299, IRM 20.2.14.6.6.1.1 classifies TC 309 as a "carryback credit" for purposes of the two-year lookback rule under IRC §6601 — the same narrow classification that applies to its Doc Code 54 sibling, carried over here because both codes generate the identical restricted-interest restatement Form 2285 computes.

The practitioner's actual next step

Ask whether a Form 2285 exists in the case file before treating a TC 309 as a simple exam reversal — the form, not the transaction code, explains how the interest computation date was derived.

Check the module's tax balance against the Form 2285 figure if a TC 309 has not posted as expected; Doc 6209's guardrail blocks the transaction when the module shows less tax than the form assumes.

Confirm the Doc Code before assuming an interest-computation-date abatement came from an examination — TC 291 and TC 299 use the identical mechanic under Doc Code 54.

On an individual account, treat a TC 309 sharing a document with an unrelated tax adjustment as a red flag rather than routine, since Doc 6209 does not permit that combination on the IMF side.

Reconstruct the exam's full sequence — the original TC 300, any carryback adjustments, and this abatement — with the IRS Transcript Decoder before treating the interest figure as final.