Mega backdoor Roth: the high earner's secret weapon

The mega backdoor Roth is a strategy that lets high earners contribute substantially more to a Roth account than the standard limits — sometimes $40,000+ per year on top of normal contributions. It only works if your employer's 401(k) plan supports two specific features.

The two requirements

1. Your 401(k) plan must allow after-tax contributions (different from Roth contributions)
2. Your plan must allow either in-service distributions to a Roth IRA, or in-plan Roth conversions

Big tech companies, large law firms, and many financial services employers commonly offer this. Smaller employers usually don't.

How the math works

The total 401(k) contribution limit (employee + employer + after-tax) was $70,000 in 2025. If you max your normal employee contribution at $23,500 and your employer adds $10,000 in matching, that leaves $36,500 of unused space you can fill with after-tax contributions, then convert to Roth.

Why it's so powerful

All of that money grows tax-free forever and comes out tax-free in retirement. For high earners maxing every other tax-advantaged account, this is one of the largest remaining buckets of tax-free growth available.