TC 300: Additional Tax Assessment by Examination or Appeals

What the code actually does

TC 300 assesses an examination deficiency. IRM 4.38.1.7.3.1.21.2 states it in the manual’s own words — "TC 300: Assesses an Examination tax deficiency on a tax module containing TC 150" — and IRS Document 6209, Section 8A says the same at greater length, describing additional tax "as a result of an Examination or Appeals Adjustment to a tax module which contains a TC 150 transaction."

It is not keyed by an account technician resolving correspondence. It comes off a closed examination, entered in Item 12 of the Form 5344 examination closing record, and its amount is the deficiency the examination determined. That provenance is the whole practical difference between this code and the adjustment code it resembles.

The posting behaviour is a checklist, not a footnote

IRM 4.38.1.7.3.1.21.2 publishes a table of what a TC 300 does to whatever else is sitting on the module, and it explains a great deal of otherwise-confusing transcript movement. Where interest is due, the TC 300 will "generate TC 336 (assessment of interest)" — so the deficiency figure a client is quoted is not the figure that lands. Where a TC 570 additional-liability freeze is present, the TC 300 will "release TC 570 freeze (additional liability pending) and refund hold." Where a TC 470 claim-pending hold is present, it releases that too.

The examination indicator itself is closed out the same way. The IRM records that with an open -L freeze the TC 300 will "generate TC 421... to release -L freeze if the Disposal Code is 1-4, 8-10, 12, 13 or 34" — the disposal-code list IRM 4.4.12.3.1 governs. A TC 300 posting without the exam indicator clearing usually means a partial assessment rather than a closed case.

One entry in the table is a genuine trap. Where an amended return freeze is present, the TC 300 will "post only if a priority code is used. PC 1&3 releases the freeze, PC 4 does not." A deficiency assessed while an amendment sits unresolved can therefore leave the module frozen behind it.

Why the provenance changes the client’s position

An examination deficiency generally cannot be assessed until the taxpayer has had the statutory notice and the chance to petition. IRC §6213 bars assessment during the ninety days after a notice of deficiency and while any timely Tax Court petition is pending. So a posted TC 300 is, in the ordinary case, evidence that the deficiency route has already run its course.

That is usually unwelcome news delivered by a transcript. By the time the code appears, the pre-assessment appeal window has generally closed, and the remaining routes — audit reconsideration, a claim for refund, collection due process on the enforcement that follows — are different remedies with different deadlines. Establishing which one is still open is the first real work on any TC 300, and the date on the code is where that starts.

The exception is worth checking every time, because it is the one that reopens everything. If the statutory notice was never issued, or was sent somewhere other than the last known address, the assessment may be invalid rather than merely unwelcome. The CP3219A statutory notice is the document to establish that against, and a client who genuinely never received one has a materially different case from a client who received it and let the ninety days run.

What TC 300 gets confused with

It gets confused with TC 290, and this is the confusion that costs clients the most. Both post additional tax against a module that already has a return; they look nearly identical in a transcript column. But a TC 290 is a data-processing adjustment, and a TC 300 is an examination or Appeals determination that reached assessment through deficiency procedures. Telling a client with a TC 300 that they can simply write to Accounts Management, or telling a client with a TC 290 that their Tax Court window has closed, are both serious errors and both start here.

It is also confused with the carryback and partial-assessment codes in the same band. The IRM’s own table separates them: the tentative-carryback codes carry an interest computation date entered in Item 11 of the closing record and adjust a prior tentative allowance, which is a different transaction from a straight deficiency. Reading the whole 30X family as one thing loses that distinction.

The practitioner’s actual next step

Establish the assessment date from the code, since every remaining remedy is measured from it rather than from when the client noticed.

Look for the interest assessment that generates alongside it before quoting the client a total.

Check whether the examination indicator actually cleared — if it did not, the case may not be closed and this may be a partial assessment.

Find out whether a notice of deficiency was issued and where it was sent, because an unreceived notice is the fact that reopens the most doors.

Confirm the whole sequence on the module with the IRS Transcript Decoder rather than from the client’s correspondence, and expect the abatement, if one is agreed, to post as TC 301 rather than as a reversal of this code.