TC 308: Additional Tax Assessment by Examination or Appeals

What the code actually does

IRS Document 6209 (the IRS’s reference guide to its data-processing codes) defines TC 308 as "Additional Tax Assessment by Examination or Appeals with Interest Computation Date," Doc Code 47 (an examination adjustment): it "inputs an Examination Deficiency of tax to a module (the IRS's record for one tax period within the account) which contains a TC 150. Generates assessment of interest from the interest computation date which must be included in the transaction... Otherwise same as TC 300." TC 300 is the general examination/Appeals assessment code, so TC 308 is functionally that assessment plus a required, specific interest start date.

Document 6209 also flags a compatibility rule worth knowing: on BMF (Business Master File) modules, TC 308 "can be used with another tax adjustment code, except TC 304, 305 or 309." TC 304 and 305 are the tentative-carryback codes; TC 309 is an examination overassessment code, not a carryback code. IRM 4.38.1.7.3.1.21.2 lists only TC 304 and 305 in its version of the exclusion. Neither source gives a reason for it.

Where TC 308 gets its interest computation date

As with TC 298, the specific interest-computation-date entry procedure this code relies on used to live in IRM 4.4.12, Examined Closings, Surveyed Claims, Partial Assessments, and Closings to Appeals. That subsection (4.4.12.5.20) is now formally marked removed, with the current text pointing to its successor: IRM 4.38.1.7.3.1.20, Item 11: Interest Computation Date. IRM 4.38.1.7.3.1.21.2 names TC 308 by number and states the requirement directly: it "must include an interest computation date, entered in Item 11 of Form 5344."

The same source also describes TC 308 as assessing "an Examination tax deficiency" specifically — which fits a code reserved for assessments that actually came out of an examination or Appeals determination, not a routine processing correction.

What this means for the account

A TC 308 on the transcript means Examination or Appeals determined a deficiency and assessed it with a specific interest start date entered on Form 5344 when the case was closed. Because this followed an actual examination, it is worth establishing whether the case was agreed or unagreed — an unagreed deficiency typically means a Notice of Deficiency and the 90-day Tax Court petition window of IRC §6213(a) preceded the assessment, which affects what can still be challenged.

As with TC 298, do not assume the interest computation date matches the return's original due date — it is a specific figure the examiner entered, and confirming it is the only reliable way to know how much interest has actually accrued.

What people mistake TC 308 for

TC 308 is easiest to confuse with TC 298, which does the same interest-computation-date-driven assessment but through routine processing rather than an examination or Appeals determination, and behaves "same as TC 290" instead of "same as TC 300." Which code is on the transcript tells a practitioner whether an actual exam or Appeals case sits behind the number.

It is also distinct from plain TC 300 — TC 308 is TC 300 with the added, mandatory interest-computation-date requirement, used specifically when the standard interest-start assumption does not apply to the case being closed.

What to do next

Establish whether the underlying case was agreed or unagreed — that history determines whether a Notice of Deficiency and Tax Court rights preceded this assessment.

Confirm the interest computation date entered on Form 5344, Item 11, rather than assuming interest runs from the return due date.

On a business account, ask whether a TC 304, 305, or 309 sits on the same document — Document 6209 flags those as incompatible with a TC 308 on the same document, so their joint appearance is worth investigating as a possible data issue.

Run the account history the client supplies through the IRS Transcript Decoder to confirm whether TC 308 or its processing-track counterpart, TC 298, actually generated the assessment.