TSP is exactly like a 401k and in fact is a 401k. Same rules apply. No need for a separate item in PL for it.

One way this is different from standard 401k’s is that TSP contributors have the ability to contribute Tax Exempt contributions into the Traditional TSP while deployed to combat zones. In that way, those contributions are able to be withdrawn tax-free; however, earnings attributed to them are taxable at withdrawal. That is referenced in the wikipedia reference that Aaron S. posted in the original suggestion.

For now you could handle this as close as possible by splitting your their TSP into multiple “accounts” in PL for each combination you have of regular vs combat excluded contributions, and Roth vs pre-tax. And then tweak the basis and taxation accordingly to get close enough.

I agree that the TSP is broadly 401(k)-like for core tax modeling, so I’m not suggesting ProjectionLab needs a completely separate retirement-account engine.

The ask is more for a TSP account subtype or preset that maps to the 401(k)-style framework but includes TSP-specific defaults and edge cases.

Reasons this matters:

Federal / military users are a large planning population, and “TSP” is how the account actually appears in their financial life. Modeling it as a generic 401(k) works mathematically in many cases, but it is less clear and less trustworthy for users. FERS/BRS matching rules are standardized enough to preset. TSP includes Agency/Service Automatic 1% contributions and, for eligible FERS/BRS participants, matching on the first 5% of pay contributed. That could be modeled manually, but it is a natural TSP preset.

Uniformed-service tax-exempt contributions are not a normal civilian 401(k) case. TSP contributions from combat-zone tax-exempt pay are also tax-exempt, and excess contributions above the elective deferral limit can go into the traditional portion from tax-exempt combat-zone pay. That creates basis/source tracking issues that a vanilla 401(k) model may not handle cleanly. TSP has its own fund menu and allocation behavior. The G/F/C/S/I funds are specific TSP investment options, and TSP’s own Roth conversion booklet says traditional and Roth TSP balances cannot have separate investment allocations; both balances are invested proportionally according to the overall account allocation. That matters if ProjectionLab lets users model different allocations by account bucket.

TSP Roth in-plan conversions are now a specific planning workflow. TSP now allows Roth in-plan conversions from traditional TSP to Roth TSP. The conversion is taxable in the year converted, taxes must be paid from outside funds, and the conversion does not count against contribution limits. That is very relevant to ProjectionLab’s optimizer/bracket-filling tools.

So I would frame the feature as: “Add TSP as a 401(k)-like plan subtype with TSP defaults,” not “create a totally separate account category.”

Minimum useful implementation:

TSP account label/type Traditional and Roth TSP buckets FERS/BRS match presets TSP fund presets or proxies: G, F, C, S, I, L Funds Optional tax-exempt military contribution/source tracking Roth in-plan conversion support Conversion optimizer support for Traditional TSP → Roth TSP Shared allocation behavior across Traditional/Roth TSP unless the user rolls funds out

The core 401(k) model may be reusable, but a TSP subtype would reduce manual work and prevent incorrect modeling for federal and military households.