Mega Backdoor Roth Calculator

A mega backdoor Roth is a strategy that lets high earners move far more than the normal Roth limit into a Roth account. You make after-tax (non-Roth) contributions to your 401(k) above the regular elective-deferral limit, then convert those after-tax dollars to Roth — either through an in-plan Roth rollover or a rollover to a Roth IRA.

Your after-tax space is the total §415(c) contribution limit of $72,000 (2026) minus your pre-tax or Roth elective deferral (up to $24,500 in 2026) and any employer match. For example, contributing the full $24,500 deferral plus a $10,000 employer match leaves $37,500 of after-tax space you could direct toward a mega backdoor Roth.

Yes. The §415(c) total limit is increased by your age-50+ catch-up, which is $8,000 for 2026, or $11,250 for those aged 60 to 63 under the SECURE 2.0 super catch-up. That additional catch-up room is added on top of the $72,000 total limit.

Your after-tax contributions (the basis) convert tax-free because you already paid tax on them. Only the earnings that accrued on those after-tax dollars before the conversion are taxable as ordinary income, at your own marginal federal tax rate. Converting promptly after each after-tax contribution minimizes the taxable gains.

Yes. For an in-plan Roth rollover, a 5-year clock starts on the conversion date, and each conversion has its own clock. If you instead roll the after-tax dollars to a Roth IRA, the after-tax basis can be withdrawn tax-free, but check your existing Roth IRA's 5-year clock for the earnings.

Yes. Your plan must allow both after-tax (non-Roth) contributions above the elective-deferral limit and a way to convert them — either in-plan Roth rollovers or in-service distributions to a Roth IRA. Many plans do not offer both features, so confirm with your plan administrator before relying on the strategy.