Mega Backdoor Roth Calculator
Last verified · Methodology
Uses the 2026 IRS limits: $24,500 for your own deferral, $72,000 for total annual additions, and catch-up contributions on top for those 50 and over.
Your 401(k) this year
The annual additions limit cannot exceed 100% of pay.
2026 limit: $24,500, not counting catch-up
Your after-tax space for 2026
$38,500
$72,000 total limit, minus $24,500 you defer and $9,000 from your employer. Converted to Roth, that is 5.1 times the $7,500 a regular backdoor Roth IRA allows.
Roth balance after 15 years
$967,467
$577,500 contributed
Growth never taxed
$389,967
Qualified Roth withdrawals are tax free
Backdoor Roth IRA alone
$188,468
$7,500 a year over the same period
Catch-up on top
None yet
Starts at 50, higher at 60 to 63
Your space at common contribution levels
Each row assumes the full $24,500 deferral in 2026 and pay of at least $72,000. Only the employer contribution changes.
| Employer contribution | After-tax space | Vs backdoor Roth IRA |
|---|---|---|
| $0 | $47,500 | 6.3x |
| $5,000 | $42,500 | 5.7x |
| $10,000 | $37,500 | 5.0x |
| $15,000 | $32,500 | 4.3x |
| $20,000 | $27,500 | 3.7x |
A larger employer match leaves less after-tax space, but it is still the better outcome: employer money is free, and after-tax space has to be funded from your own pay.
What it adds up to
With $38,500 a year going into Roth money for 15 years at a 7% return, the balance reaches about $967,000. Of that, $577,500 is your contributions and about $390,000 is growth that will never be taxed on a qualified withdrawal. The regular backdoor Roth IRA, at $7,500 a year over the same period, reaches about $188,000.
The order to fund things in
- Contribute enough to get the full employer match.
- Fill the regular $24,500 deferral, pre-tax or Roth.
- Fund a backdoor Roth IRA if your income is above the direct Roth IRA limits.
- Then use after-tax space for the mega backdoor.
After-tax contributions come from take-home pay, so this only makes sense once an emergency fund is in place and there is no high-interest debt. For the regular deferral side, the 401(k) calculator projects the full account, and the Roth vs traditional 401(k) comparison helps decide how to split the first $24,500.
It is a way to put far more money into Roth accounts than the normal limits allow. You make after-tax (not Roth) contributions to your 401(k) above your regular deferral, then convert them to Roth, either inside the plan or by rolling them to a Roth IRA. Once converted, future growth is tax free on qualified withdrawals.
Your own pre-tax or Roth deferral is capped at $24,500. Total annual additions to the plan, meaning your deferral plus employer contributions plus after-tax contributions, are capped at $72,000 or 100% of your pay, whichever is lower. Catch-up contributions of $8,000 at 50 and over, or $11,250 at ages 60 to 63, are allowed on top and do not count toward the $72,000.
Only if it permits after-tax contributions beyond the regular deferral, and also permits either in-plan Roth conversions or in-service withdrawals of those after-tax dollars. Many plans offer neither. The summary plan description will say, or HR or the plan administrator can confirm.
Not on the contributions themselves, because they were made with after-tax money. You do owe ordinary income tax on any earnings between the contribution and the conversion. Converting quickly, or using a plan feature that converts automatically, keeps that taxable amount close to zero.
Plans must pass nondiscrimination testing on after-tax and matching contributions. If lower-paid employees do not contribute enough, the plan may cap or refund after-tax contributions from highly compensated employees. The calculator shows the legal space; your plan may allow less.
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