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How much room is there for a mega backdoor Roth?

Some 401(k) plans accept after-tax contributions beyond your regular salary deferrals, up to the overall annual additions limit. Converting or rolling those dollars to Roth is the “mega backdoor”. Check your 2026 room and how a transfer would split.

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YOUR NUMBERS

Find the room beyond salary deferrals.

Check 2026 voluntary after-tax 401(k) contribution room, then explore an eligible direct conversion or rollover.

Example values. Edit them or choose Clear inputs to start your own case.

1. Your 2026 contributions

Include contributions already made plus amounts planned for the rest of the year. Enter a confirmed zero when none apply.

Age at year-end 2026Plan-eligible W-2 compensation ($)Regular pretax + Roth salary deferrals ($)Exclude catch-up contributions.Catch-up contributions ($)Employer contributions + forfeitures ($)Voluntary non-Roth after-tax contributions ($)Lower annual after-tax plan cap ($)OptionalLeave blank only if your administrator confirms there is no lower cap.

2. What your plan permits

Your plan administrator can confirm these provisions. Unknown answers remain incomplete.

Voluntary non-Roth after-tax contributions?OptionalIn-plan Roth conversions?OptionalEligible in-service rollovers?OptionalThis is an ordinary calendar-year 401(k) for a W-2 employee. I confirmed eligibility, payroll and nondiscrimination limits, including any lower cap entered above.I included this employer’s and related employers’ contributions. There are no other-employer salary deferrals requiring coordination.

4. Optional direct-transfer illustration

Proposed routeOptionalAfter-tax basis allocated to this distribution ($)OptionalAll pretax dollars allocated to this distribution ($)OptionalInclude earnings and any other required pro-rata pretax allocation. Do not assume you can withdraw only basis.The administrator confirmed vested rollover eligibility, basis, all required pretax allocation and direct transfers. No RMD or corrective distribution is included.Administrator permits this coordinated split rollover?Optional

WORKED EXAMPLE

The example, step by step.

The situation

Age 35 with $300,000 of plan-eligible pay
$24,500 of salary deferrals and $12,000 of employer contributions in 2026
A plan that allows after-tax contributions, in-plan conversions and in-service rollovers

What the calculator finds

2026 annual additions limit: $72,000, with $36,500 already used.
Room for after-tax contributions: $35,500, subject to your plan’s own limits.
A $36,000 split rollover sends $35,500 of after-tax basis to a Roth IRA and $500 of pretax earnings to a traditional IRA, with no taxable income from the transfer.

A Roth salary deferral and a voluntary after-tax contribution are different. A rollover does not refill your contribution allowance.

HOW IT WORKS

What goes in.
What comes out.

Enter your age, plan-eligible pay and this year’s salary deferrals, catch-up, employer and after-tax contributions. The calculator applies the 2026 limits to find the room left under the annual additions limit.

Answer what your plan permits. Unknown answers keep the result incomplete instead of guessing.

Optionally describe a direct transfer to see how basis and earnings would move between Roth and traditional accounts, and how much would be taxable.

KNOW THE LIMITS

What it does not cover.

Plan rules, nondiscrimination testing and administrator processing can lower your room. Confirm them with your plan.
A rollover does not create new contribution room.
Pretax money sent to a traditional IRA can affect later backdoor IRA conversions under the pro-rata rule.

Questions

What is a mega backdoor Roth?

Making voluntary after-tax 401(k) contributions beyond your pretax and Roth salary deferrals, then converting them to Roth inside the plan or rolling them to a Roth IRA. Your plan has to allow both steps.

What is the 2026 limit?

For 2026, total employee and employer additions to a defined contribution plan are limited to $72,000, or 100% of pay if less, not counting age-based catch-up contributions. Regular salary deferrals are limited to $24,500.

Is a mega backdoor Roth the same as a backdoor Roth IRA?

No. A backdoor Roth IRA is a nondeductible IRA contribution followed by a conversion. The mega backdoor uses after-tax 401(k) contributions and can involve much larger amounts.

WHEN YOU’RE READY FOR MORE CONTEXT

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