The Megabackoor Roth strategy allows some retirement savers to contribute significant sums of money on a Roth (after tax) basis. I'll explain why it's called the Megabackdoor Roth and who this rule applies to.  To participate in this strategy, your 401k plan must allow for after-tax contributions, as well as either in-plan Roth conversions OR in-service withdrawals.  If you're eligible, you may be able to get more than 4x the annual contribution limit of a Roth IRA growing tax-free!