Mega Backdoor Roth Calculator

High-savers who've already maxed their regular 401(k) and want to put even more into a Roth. The mega backdoor Roth can move tens of thousands of extra dollars into tax-free accounts each year — but only if your employer's plan supports it.

There are two 401(k) limits: the employee deferral limit (what you contribute pre-tax or Roth) and a much higher overall limit that also includes employer contributions and after-tax contributions. The gap between the two — after subtracting your deferral and any employer match — is room you can fill with after-tax contributions.

You then convert those after-tax dollars to Roth, either through an in-plan Roth conversion or by rolling them out to a Roth IRA. The result: far more tax-free retirement savings than the normal limits allow.

Your 401(k) plan must allow both after-tax contributions and either in-plan Roth conversions or in-service withdrawals. Many plans don't offer these features, so check your plan documents or ask HR before counting on this strategy.

This uses the overall defined-contribution limit and excludes the age-50 catch-up. The 2026 limits are estimates pending verification and change most years. Converting after-tax gains (as opposed to contributions) can trigger some tax. Confirm the mechanics with your plan and a tax professional.