Mega backdoor Roth calculator

2026 415(c) cap $72,000, elective $24,500, catch-up outside that cap. Read the mega backdoor guide if after-tax vs Roth elective is new. This does not talk to your recordkeeper.

Quick answer: This calculator estimates leftover after-tax 401(k) room under the annual-addition cap printed on the page, keeps catch-up outside that cap, and estimates tax on after-tax earnings you have not converted.

Age band Elective deferral this year (pre-tax + Roth 401(k), not catch-up) Catch-up this year Employer match + profit sharing After-tax you plan to add

Plan allows after-tax employee money? In-plan Roth conversion or in-service rollover to Roth IRA? After-tax basis already sitting in the plan Earnings in that after-tax source Ordinary tax rate on those earnings %

2026 result

Educational estimate. 415(c) $72,000 and elective $24,500 from IRS Notice 2025-67. Catch-up $8,000 / $11,250 is modeled outside 415(c). Sequence if payroll is messy: PayPal playbook.

What this means for you

What this means for you: room is the cap minus elective deferrals and employer money, not minus catch-up. After-tax contributions only work if the plan allows them and allows a conversion. The cap figure was not changed in this review.

How to use this calculator

Open the Mega backdoor Roth calculator and keep the sample numbers or replace them with your own. The result updates as you type.
Read the headline figure first, then the breakdown or chart under it.
Use Copy share link if you want those inputs in the URL. The page is an educational estimate, not a filing, approval, or recommendation.

FAQ

What is mega backdoor room?

The leftover under the annual-addition limit after employee deferrals and employer contributions, for after-tax dollars the plan may allow.

Does catch-up use that same cap?

This page keeps catch-up outside the annual-addition cap, which is how the page's note describes the limit.

Are after-tax earnings tax-free?

Not until they are in Roth. The page estimates ordinary tax on earnings you have not converted, at the rate you type.

Educational, not financial advice. Page updated October 24, 2026 — no tax, limit, or rate figure was changed in this review.