The Mega Backdoor Roth Move That Lets a Married Couple in the Same Plan Stack $94,000 of Tax-Free Contributions in One Year

The IRS sets a $72,000 per-employee annual limit on total 401(k) contributions, including employee deferrals, employer match, and after-tax contributions. With two spouses working at the same employer and using the same plan, each spouse can fill the limit separately, creating substantial after-tax contribution room. After the $24,500 employee deferral and an estimated employer match, remaining after-tax room can be contributed and then converted to Roth. After-tax contributions grow taxable until converted, and earnings between contribution and conversion are taxed as ordinary income at conversion. Converting in the same pay cycle reduces taxable earnings. Plan rules and administrator procedures determine how quickly conversions can be processed.

"The IRS sets a separate cap on total contributions to a single participant's 401(k). For 2026, the figure is $72,000 per employee under IRC §415(c). That covers employee deferrals, employer match, and after-tax contributions combined. It is a per-person limit, not a per-couple limit, which is the entire point of running the play twice in the same household."

"The main point is that each spouse fills the bucket this way, and the $24,500 employee deferral takes the first slot. Roughly $11,000 in employer match takes the second, assuming a 6% formula on $185,000 of pay. That leaves $36,500 of after-tax room before hitting $72,000. Two spouses, same plan, same rules, and the household creates $73,000 a year in after-tax dollars that can be converted to Roth."

"After-tax money sitting in the plan grows taxable until it is converted, and any earnings on the basis between contribution and conversion become ordinary income at conversion. The fix is mechanical, as most plans that allow after-tax contributions also allow either an in-plan Roth conversion or an in-service rollover to a Roth IRA. The couple wants the conversion to happen in the same pay cycle as the contribution."

"If a $1,500 after-tax contribution sits in a money market sleeve for two weeks and earns $4, the $4 is taxable. If it sits for six months and earns $400, the $400 is taxable. Plan administrators handle this differently. Some re"

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