Mega Backdoor Roth Calculator United States
This mega backdoor Roth calculator shows the after-tax money you can convert to Roth in 2026: the 415(c) limit minus 401(k) deferrals and employer match.
What it does
The Mega Backdoor Roth Calculator works out how much after-tax money you can add to your 401(k) and convert to Roth, using the overall defined-contribution (415(c)) limit minus your elective deferral and employer contributions.
Data sources & parameters
The figures below drive this calculator. We keep them aligned with the latest official guidance, and each result recalculates automatically whenever a value changes.
| Parameter | Value | Source | Last updated |
|---|---|---|---|
| Annual additions limit for a defined contribution plan (IRC 415(c)(1)(A)) | 72,000 | irs.gov | Effective 2026-01-01 |
| Elective deferral limit (IRC 402(g)(1)); the same dollar amount applies by statute to 403(b) deferrals and to 457(b) deferrals under IRC 457(e)(15) | 24,500 | irs.gov | Effective 2026-01-01 |
| Elective deferral limit plus the age-50 catch-up (IRC 402(g)(1) with 414(v)(2)(B)(i)) | 32,500 | irs.gov | Effective 2026-01-01 |
| Catch-up age bands: the standard catch-up opens at age 50 (IRC 414(v)(2)(B)) and the higher SECURE 2.0 catch-up applies for ages 60 to 63 (IRC 414(v)(2)(E)) | Rate schedule | irs.gov | Effective 2026-01-01Seeded from the IRS catch-up rules: age 50 for the standard catch-up, ages 60-63 for the higher SECURE 2.0 catch-up; previously hardcoded in catch-up-contribution-us and 401k-calculator-us. Values unchanged. |
| Catch-up contribution limit for ages 60 to 63, applicable employer plans other than SIMPLE (IRC 414(v)(2)(E)(i)) | 11,250 | irs.gov | Effective 2026-01-01Verified 2026-09-06 against the IRS 2026 retirement limits release: the ages 60-63 catch-up remains $11,250 instead of $8,000. |
We always strive to use the latest data for every variable so our results and reports are as accurate as possible. Even so, errors are possible — you should not rely on this tool or its report alone, and we accept no liability for any decision made based on it.
The formula
After-tax room = 415(c) limit - min(deferral, elective base limit) - employer match
How it works
It subtracts the elective deferral that counts against the 415(c) limit and your employer contributions from the overall limit, leaving the after-tax room you can contribute and convert to Roth.
Where it is used
- Sizing an after-tax 401(k) contribution
- Planning a mega backdoor Roth conversion
- Checking how much of the 415(c) limit is left
Worked example
At age 45 deferring $24,500.00 with $10,000.00 of employer money, … of after-tax room remains — the amount you could contribute and convert to Roth against the … ceiling.
What the mega backdoor Roth calculator does
The calculator works out how much after-tax money you can add to your 401(k) and convert to Roth in one year. It starts from the overall defined-contribution limit in Section 415(c) of the tax code and subtracts the elective deferral that counts against it and your employer contributions. The remainder is your after-tax contribution room, the most you could convert through a mega backdoor Roth.
For high earners this can move large sums into Roth accounts, but several limits interact and the room is easy to miscalculate. Besides the room, the tool shows the overall ceiling, how much of your deferral counted, the total contribution if you fill the room and the share of the ceiling already used.
How the numbers fit together
Two limits apply. The elective deferral limit caps what you choose to defer into the plan, pre-tax or Roth. The Section 415(c) limit caps everything that goes into your account in a year: your deferrals, your employer's contributions and any after-tax contributions.
The mega backdoor Roth uses the gap between them. After your deferral and your employer's contribution, there is usually space left under the 415(c) ceiling. After-tax contributions can fill it, and if your plan allows, you convert them to Roth. The calculator measures that gap.
Why catch-up contributions are treated separately
At 50 or older you can make catch-up contributions above the standard deferral limit, and from age 60 to 63 the larger SECURE 2.0 catch-up applies. Catch-up dollars sit on top of the 415(c) limit, not inside it, so they raise your overall ceiling without reducing your after-tax room.
The calculator counts your elective deferral only up to the base under-50 limit when it computes the room. Anything above that is catch-up and is added to the ceiling. An older saver using the catch-up therefore has a higher ceiling and at least as much after-tax room as a younger saver with the same base deferral. The overall ceiling in the results shows whether the catch-up was added.
Reading the results
The after-tax room is the main output: the after-tax amount you can contribute this year, and the most you can convert if you convert all of it. The maximum Roth conversion figure subtracts any after-tax dollars you have already contributed, so it shows the room left now.
The overall ceiling is the full 415(c) limit for your situation, including the catch-up if you are 50 or older, or the larger catch-up from 60 to 63. The elective deferral counted shows how much of your deferral was applied against the 415(c) limit. The projected total contribution adds your deferral, your employer contribution and the after-tax room, which is what would go into the account if you fill the room. The share of the ceiling used shows how much of the limit your deferral and employer money take up before any after-tax contribution.
Getting the inputs right
Enter your age so the tool knows whether to apply the catch-up. For the deferral, enter what you put into the 401(k) from your paycheck, pre-tax and Roth combined. For the employer contribution, enter everything your employer puts in, including profit-sharing or non-elective amounts, because all of it counts against the 415(c) ceiling.
If you have already made after-tax contributions this year, enter them in the advanced field so the calculator shows the room you have left. Be precise: the aim is to fill the account up to the 415(c) limit without going over.
Practical cautions
Your 401(k) must allow after-tax contributions above the elective deferral limit and offer either in-plan Roth conversions or in-service withdrawals that let you roll the after-tax money into a Roth IRA. Many plans do not, so check with your plan administrator first.
Timing affects the tax. Converting the after-tax contributions themselves is generally tax-free, but earnings that build up before you convert are taxable on conversion, so many people convert soon after contributing. This tool does not calculate tax on earnings.
The figures are based on the current IRS limits, which are indexed each year, and on the amounts you enter. The result is not tax or financial advice. Confirm your plan's rules and the current limits with official IRS sources and your plan administrator before acting.
About This Mega Backdoor Roth Calculator
Use this mega backdoor Roth calculator to get an instant, accurate estimate. The figures follow official IRS guidance and every rate and threshold is kept up to date for 2026. Adjust the inputs above to match your situation, or browse all our calculators to plan your next step.
Tax year 2026
Frequently asked questions
What is a mega backdoor Roth?
How is the after-tax room calculated?
Do catch-up contributions count against the 415(c) limit?
Is the conversion itself taxable?
Does my plan have to allow this?
Is my data private?
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