Mega Backdoor Roth
Also called: mega backdoor, after-tax 401k conversion
A mega backdoor Roth uses after-tax 401(k) contributions above the normal deferral limit, then converts them to Roth — potentially sheltering tens of thousands more per year. It only works if your plan permits both after-tax contributions and in-service conversions, which most don't. Where available it's the largest tax-free savings opportunity in the US system, and worth asking your plan administrator about explicitly.