Mega Backdoor Roth Calculator
See how much you can move into a Roth through the mega backdoor strategy in 2026, from your 401(k) deferrals, employer match, and the Section 415(c) limit.
Mega Backdoor Roth Calculator
Tax Year
Your Age
Age at year-end 2026. This sets your catch-up deferral tier (it does not change after-tax room).
Your 2026 401(k) Deferrals
Pre-tax plus Roth employee contributions only. Capped at the 2026 limit of $24,500 (exclude catch-up dollars).
Employer Match + Profit Sharing
All employer money for 2026. It counts against the $72,000 limit and shrinks your after-tax room.
Plan Features
Both must be true for the mega backdoor Roth to work, regardless of your computed room.
After-tax room is the space left under the $72,000 limit. Catch-up contributions add to your deferral capacity but not to this after-tax number.
Notes
- Convert after-tax money to Roth quickly. Contributions convert tax-free, but any earnings before conversion are taxed as ordinary income.
- If you are 50 or older and your prior-year wages were over $150,000, SECURE 2.0 requires catch-up contributions to be Roth. This does not change your after-tax room.
- Estimates only, not tax or legal advice. Plan rules vary, so confirm the after-tax and conversion features with your plan administrator.
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How the mega backdoor Roth works in 2026
The mega backdoor Roth is a way to push a large amount of money into a Roth account through your workplace 401(k). You make after-tax (non-Roth) contributions on top of your regular deferrals, then convert that money to Roth, either with an in-plan Roth conversion or an in-service withdrawal rolled to a Roth IRA. Once it lands in Roth, future growth and qualified withdrawals come out tax-free.
Three things have to line up. Your plan must allow after-tax contributions, it must allow a conversion or in-service withdrawal, and there has to be room under the IRS Section 415(c) total-additions limit, which is $72,000 for 2026. That $72,000 ceiling covers everything that goes into your 401(k) for the year: your deferrals, employer money, and after-tax contributions combined.
Calculating your after-tax 401(k) room
The math is short. Start at the $72,000 limit, then subtract your employee deferrals and all employer contributions:
After-tax room = $72,000 − employee deferrals − employer contributions
With a maxed $24,500 deferral and no employer match, your room is $72,000 minus $24,500, which is $47,500. Add an employer match and that room shrinks dollar for dollar. Say you get a $10,000 employer contribution alongside a maxed deferral: that leaves $37,500 of after-tax space ($72,000 − $24,500 − $10,000). If your deferrals plus employer money already reach $72,000, your after-tax room is $0.
Where catch-up contributions fit (and where they don't)
This is the part people get wrong. Age 50-plus catch-up contributions ($8,000 for 2026) and the age 60 to 63 super catch-up ($11,250 under SECURE 2.0) raise how much you can defer, but they count against the elective deferral limit, not the $72,000 Section 415(c) limit. So they don't add to your after-tax mega backdoor space.
In practice, total dollars in the plan can reach $80,000 at age 50-plus or $83,250 at age 60 to 63, but the after-tax portion still works off the $72,000 base. One more rule worth knowing: if you are 50 or older and earned $150,000 or more in the prior year, SECURE 2.0 requires your catch-up to be Roth. That changes how the catch-up is taxed, not your after-tax room.
Steps and pitfalls
First, confirm your plan actually supports both after-tax contributions and a conversion route. Plenty of plans don't, and the strategy simply doesn't work without them. Second, convert quickly. After-tax contributions convert tax-free, but any earnings that build up before the conversion are taxed as ordinary income, so converting soon after each contribution keeps the taxable growth small.
There is no income limit on the mega backdoor Roth, which is why high earners who are phased out of direct Roth IRA contributions still use it. If you are checking how a Roth conversion stacks on top of your income, the Roth IRA Conversion Calculator walks through the bracket math, and the MAGI Calculator shows where your direct Roth IRA phase-out falls. For a complete federal refund estimate, you can also run the numbers in Tax47. These figures are estimates only and not tax or legal advice.
Frequently Asked Questions
Common questions about mega backdoor roth calculator
What is a mega backdoor Roth and how is it different from a regular backdoor Roth?
A mega backdoor Roth uses after-tax contributions inside a 401(k), then converts that money to Roth, moving up to about $47,500 a year (with no employer match). A regular backdoor Roth works through a Traditional IRA and is capped at the much smaller IRA limit of $7,500 for 2026. The mega version moves a lot more, but only if your 401(k) plan supports it. See the Roth IRA Conversion Calculator for the IRA side.
How much can I contribute to a mega backdoor Roth in 2026?
Start with the 2026 Section 415(c) total-additions limit of $72,000, then subtract your employee 401(k) deferrals and all employer contributions. With a maxed $24,500 deferral and no employer match, your after-tax room is $72,000 minus $24,500, or $47,500. Employer match and profit sharing cut into that number dollar for dollar.
Does my catch-up contribution increase my mega backdoor Roth room?
No. Catch-up contributions ($8,000 at age 50 to 59 and 64 plus, or $11,250 at age 60 to 63) count against the elective deferral limit, not the $72,000 Section 415(c) limit. They raise how much pre-tax or Roth you can defer, but they don't add to your after-tax mega backdoor space. The $72,000 cap is still the binding limit on the after-tax portion.
What does my 401(k) plan need to allow for the mega backdoor Roth to work?
Two things. First, the plan has to accept after-tax (non-Roth) contributions beyond your regular deferrals. Second, it has to allow either an in-plan Roth conversion or an in-service withdrawal so you can move that money into Roth. If either one is missing, the strategy doesn't work no matter what the math shows. Ask your plan administrator or check the summary plan description.
Is there an income limit on the mega backdoor Roth?
No. Unlike direct Roth IRA contributions, which phase out at higher incomes, the mega backdoor Roth has no income ceiling. High earners who are shut out of regular Roth IRA contributions can still use it. Check your Roth IRA phase-out separately with the MAGI Calculator.
Do I owe taxes when I convert after-tax 401(k) money to Roth?
Your after-tax contributions convert tax-free, since you already paid tax on those dollars. Any earnings that build up before you convert are taxed as ordinary income at conversion. Converting quickly, ideally right after each contribution, keeps the taxable growth small.
Does the employer match reduce my mega backdoor Roth space?
Yes. All employer money, including match and profit sharing, counts toward the $72,000 Section 415(c) limit. A bigger employer contribution leaves less room for after-tax contributions. If your deferrals plus employer money already hit $72,000, your after-tax room is $0.
Can I do a mega backdoor Roth if I'm self-employed?
Possibly. A solo 401(k) can support the strategy if the plan document allows after-tax contributions plus in-plan conversions or in-service withdrawals. Many basic solo 401(k) providers don't offer these features, so you may need a plan with a custom document. If you are weighing early access tradeoffs, the 401(k) Early Withdrawal Penalty Calculator can help.