Please elaborate on how you would like this to function. Megabackdoor modeling is already something you can do with Flows.

Thanks — I should have been more precise. I’m not asking about Mega Backdoor Roth modeling.

The use case is Roth in-plan conversion of existing pre-tax employer-plan balances, such as Traditional TSP → Roth TSP, or similar 401(k)/governmental 457(b) plans where the plan supports it.

This is financially different from a mega backdoor Roth. Mega backdoor Roth is a contribution-space strategy: after-tax current-year contributions are converted to Roth. An in-plan Roth conversion is a tax-bracket planning strategy: existing pre-tax plan assets are converted to the Roth subaccount inside the same plan, generating ordinary taxable income in the conversion year, with taxes ideally paid from taxable cash/outside funds.

The planning issue is that this should not be modeled as a new contribution, an IRA rollover, or a withdrawal used for spending. It should be a taxable internal transfer from a pre-tax plan subaccount to a Roth plan subaccount.

What would be useful in ProjectionLab is something like:

Account-level setting: “This plan supports Roth in-plan conversions.” Paired pre-tax/Roth buckets inside the same employer plan. Manual annual conversion amounts and optimizer support for bracket-filling. Tax treatment as ordinary income in the conversion year. Taxes paid from outside cash/cash-flow, not withheld from the converted amount. No contribution-limit impact. Preserved plan identity, rather than treating the move as a Roth IRA contribution or external rollover.

The reason this matters for the new optimizing tools is that the optimizer may recommend Roth conversions during low-income years, but for users with large TSP/457(b)/401(k)-style balances, the correct destination may be the plan’s Roth subaccount, not a Roth IRA and not a mega backdoor flow.