Mega Backdoor Roth Calculator
Calculate the extra after-tax 401(k) contributions you can make and convert to Roth, on top of your normal deferral and employer match.
After-tax Roth capacity $39,500.00
Employer match $8,000.00
Total 401(k) additions limit $72,000.00
How it's calculated
Your after-tax capacity is the §415(c) total-additions limit minus your elective deferral minus your employer match. Whatever is left is room you can fill with after-tax dollars and convert to Roth.
Assumptions
- Uses the 2026 total defined-contribution limit of $72,000 (§415(c)). — IRS Rev. Proc. 2025-32
- Only usable if your plan allows after-tax contributions AND in-plan Roth conversion. Confirm with your plan administrator.
Last updated: 2026-08-07 · Tax year 2026
These assumptions follow our general methodology.
Frequently asked questions
How do I know if my plan supports this?
Ask your plan administrator two things: does the plan allow after-tax (non-Roth) contributions, and does it allow in-plan Roth conversions or in-service withdrawals? You need both.
Is this the same as a backdoor Roth IRA?
No. The mega backdoor uses your 401(k) and much higher limits; the backdoor Roth IRA uses an IRA and the $7,500 limit.
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