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
$
Remaining paychecks14
Calculator result
After-tax Mega Backdoor contribution to go
$57,000
after-tax per future paycheck
42.3%
for the next 14 paychecks
$10,000$5,000$57,000
Contribution typeContribution so farContribution to go
Pre-tax / Roth
%$
%$
My company matches%of my base salary, up to%of salary.
Employer match
%$
0%
$0
After-tax
%$
42.3%
$57,000
30-year tax impact
Invest $57,000 at 7% annually. Taxable gains assume 22% tax.
30 years
Taxable account
After estimated $82,918 tax drag
$350,981
Mega Backdoor Roth
Qualified Roth growth tax-free
$433,899
Roth advantage
+$82,918
Potential extra take-home value when Roth rules are met.
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.