Retirement · Calculator

Mega backdoor Roth
capacity.

If your 401(k) plan allows after-tax contributions and in-service rollovers, you can shelter tens of thousands more per year in a Roth wrapper than the standard limit. This tool shows your remaining capacity.

The question it answersHow much mega backdoor Roth capacity do I have left this year?

Tax year: models 2026 figures; check the assumptions before using it for another year. Privacy: runs in your browser. What you enter stays on your device unless you copy a share link, which puts your inputs in the link.

This page covers US-specific 401(k) rules. The mega backdoor Roth is unique to the US 401(k) / 403(b) / solo 401(k) structure. It does not exist in other countries' workplace retirement systems.

AGE

Age 50+ unlocks catch-up contributions.

ANNUAL SALARY ($)

YOUR 401(K) CONTRIBUTION ($)

2026 limit: $24,500 ($32,500 with 50+ catch-up, $35,750 at ages 60 to 63).

EMPLOYER MATCH ($/YR)

YEARS OF MEGA BACKDOOR USE

EXPECTED ANNUAL RETURN (%)

Check with your plan administrator whether both (a) after-tax contributions are allowed, and (b) in-service rollovers or in-plan conversions are allowed. Without both, the mega backdoor is not available.

YOUR MEGA BACKDOOR CAPACITY

per year of additional tax-free savings room.

TOTAL 401(K) LIMIT

$72,000

YOUR CONTRIBUTION

EMPLOYER MATCH

REMAINING CAPACITY

LIFETIME IMPACT

Enter values to see projection.

Estimate, not tax or legal advice. It applies the 2026 rules listed in the assumptions to the numbers you enter. Details this tool does not model can change the result.

What this tool assumes

2026 total 401(k) contribution limit (415(c)): $72,000; catch-up at 50+ adds $8,000 for $80,000 total, or $11,250 for $83,250 at ages 60 to 63.
2026 employee elective-deferral limit (402(g)): $24,500; catch-up at 50+ adds $8,000 for $32,500 total, or $11,250 for $35,750 at ages 60 to 63.
Mega backdoor is only possible if your plan allows after-tax contributions and in-service conversions or rollovers.
After-tax contributions can exceed the employee contribution limit up to the total plan limit.
In-service rollover or in-plan conversion moves after-tax dollars to Roth immediately; earnings before the conversion are taxable.

Room left under the $72,000/yr limit

Under 50tool defaults

$24,500/yr$41,500/yr capacityEmployee limit

$0$72,000/yr total limit

$24,500/yr your 401(k) contribution$6,000/yr employer match$41,500/yr after-tax room: your mega backdoor capacity

Then the after-tax dollars move to Roth

Plan feature 1After-tax contributionsCan exceed the employee limit

Plan feature 2In-service rollover or in-plan conversionMoves the dollars to Roth right away

ResultRothQualified withdrawals tax-free

Earnings before the conversion are taxable. Without both plan features, the mega backdoor is not available.

At the tool's defaults, a $24,500/yr contribution and a $6,000/yr match use part of the $72,000/yr total limit, leaving $41,500/yr of after-tax room. If the plan allows both features, that room moves to Roth, where qualified withdrawals are tax-free.

The mega backdoor Roth is one of the most powerful retirement tools available to US W-2 employees. Educational only; not financial advice.

HOW THIS IS CALCULATED

This tool runs entirely in your browser: no data is sent to any server. The assumptions and default values behind the result are listed under “What this tool assumes” on this page. Verify the methodology or inspect the source code in your browser's dev tools.

Mega backdoor Rothcapacity.

Where to go from here

Mega backdoor Roth
capacity.