Mega Backdoor Roth Calculator

See how much after-tax 401(k) room you have left this year, on top of your regular contribution.

Age

Your elective deferral this year ($)

Pretax + Roth 401(k) contributions combined.

Employer match / profit-sharing this year ($)

My plan allows after-tax (non-Roth) 401(k) contributions

Combined 415(c) limit for your age (2026)

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After-tax mega backdoor room available

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Educational estimate, not tax advice — actual room depends on your specific plan document. Not every 401(k) plan allows after-tax contributions or in-service withdrawals/in-plan Roth conversions; call your plan administrator to confirm before assuming this room is usable.