This is a short, honest note on a risk worth understanding — not a reason to panic, and not a prediction. The Mega Backdoor Roth depends on a feature (after-tax contributions plus conversion) that Congress has, at one point, proposed to curtail.
What happened
During the Build Back Better debates around 2021, draft legislation included provisions that would have restricted after-tax 401(k)-to-Roth conversions — effectively closing the Mega Backdoor Roth for many savers. Those provisions did not become law. As of this writing, the strategy remains available where plans support it.
What it means for planning
- It is current law, not a loophole that is closing tomorrow. Treat it as available now while remaining aware it has been targeted before.
- The mechanics are evergreen even if the conversion changes. After-tax contributions, basis tracking, and Form 8606 reconciliation are general 401(k) concepts that survive regardless of any specific Mega-Backdoor rule change.
- Use it while it is available, but don't over-commit on the assumption it is permanent.Keep liquidity and don't build a plan that breaks if the rule changes.
Honesty note
We do not forecast legislation. We flag that this risk is non-zero over a multi-year horizon, point you to current law, and update this page if the rules change. For decisions that hinge on the strategy persisting, talk to a CFP or CPA who tracks pending tax legislation.