Why it exists
The normal employee 401(k) limit is separate from the larger annual overall plan limit. If your plan allows after-tax contributions, unused space can become Roth savings.
Mega Backdoor Roth Calculator (2026) | How Much Room Do I Have Left?
Find your remaining Mega Backdoor space in under 30 seconds.
Estimate how much after-tax 401(k) room you may still have after your employee contribution and employer match.
Mega Backdoor Roth Contribution Limit Calculator
IRS limit - pre-tax/Roth - employer match = after-tax limit
After-tax money plus in-plan Roth conversion gives us Mega Backdoor Roth.
2026 IRS overall limitIRS Notice 2025-67
$
2026 IRS default pre-tax limit
$
Salary paid so far
$92,308
Remaining salary this year
$107,692
Remaining paychecks14
Calculator result
After-tax Mega Backdoor contribution to go
$44,000
after-tax per future paycheck40.9%for the next 14 paychecks
Total after-tax
$44,000
Already contributed plus room to go.
Contribution breakdown
Mega Backdoor$44,000
Employer match$8,000
Pre-tax / Roth$20,000
Contribution typeContribution so farContribution to go
Pre-tax / Roth
Contribution so far
Contribution to go
Employer match formula
My company matches%of pre-tax contribution, up to%of base salary$8,000
Estimated from total annual pre-tax contributions with the cap applied once.
Tip: contribute 4% ($4,308) for remaining pre-tax contributions to get the full company match benefit.
Employer match
Contribution so far
$4,616
Contribution to go
$3,384
Employer match to go is capped because the annual employer match cap has been reached.
After-tax
Contribution so far
Contribution to go
After-tax to go
$44,000
40.9% of remaining payroll
Total After-Tax (Mega Backdoor) Contribution
After-tax already contributed plus recommended additional after-tax contribution.
Total after-tax
$44,000
Estimated 30-Year Take-Home Difference
Compares the total after-tax contribution shown above in Mega Backdoor Roth versus a normal taxable account.
30 years
Normal taxable investment
$276,751
Mega Backdoor Roth
$334,939
Take-home advantage
$58,188
Assumes 7% annual return over 30 years. Mega Backdoor Roth growth is treated as tax-free, while the taxable account applies a 20% tax rate to investment gains.
How it works
1. Pre-tax / Roth
Contribute enough to capture the full employer match.
2. Employer match
Your company match uses part of the overall IRS 401(k) limit.
3. After-tax
Remaining room can become Mega Backdoor Roth when your plan supports it.
Plain English
What is Mega Backdoor Roth?
Mega Backdoor Roth lets some employees contribute extra after-tax money to a 401(k), then convert it into a Roth account.
Requirements
- Your employer offers after-tax 401(k) contributions.
- Your plan allows in-plan Roth conversion or in-service withdrawal.
- You understand how your employer match affects the annual limit.
Big tech plans to check
Mega Backdoor Roth features are often discussed by employees at large tech companies, but your current plan document is the source of truth.
Questions
FAQ
Does employer match count?
Yes. Employer match reduces the amount available for Mega Backdoor Roth contributions.
What is after-tax contribution?
It is money contributed to your 401(k) after income tax, separate from pre-tax and Roth employee deferrals.
What is Roth conversion?
It moves eligible after-tax 401(k) money into a Roth account so future qualified growth can be tax-free.
What happens after age 50?
Catch-up contribution rules may apply. Check current IRS guidance and your plan documents.