How the Mega Backdoor Roth Calculator Works
The mega backdoor Roth strategy lets high earners contribute far more to Roth accounts than standard limits allow, by making after-tax 401(k) contributions and converting them to Roth.
This mega backdoor Roth calculator computes:
- Max After-Tax (Mega Backdoor) Contribution — your remaining contribution room
- Total Contribution Room Used — combined employee, employer, and after-tax amounts
- Projected Value of After-Tax Contributions — what the converted funds could grow to
- Projected Tax-Free Growth — the investment gains on those contributions
Mega Backdoor Roth Formula
After-Tax Room = (Overall 415(c) Limit + Catch-Up) − Employee Contribution − Employer Contribution
Mega Backdoor Roth Examples
Example 1: High Earner, No Catch-Up
| Variable | Value |
|---|---|
| Employee Contribution | $23,500 |
| Employer Contribution | $8,000 |
| Overall Limit | $70,000 |
| After-Tax Room | $38,500 |
Example 2: High Earner, Age 50+
| Variable | Value |
|---|---|
| Employee Contribution | $31,000 |
| Employer Contribution | $10,000 |
| Overall Limit | $70,000 |
| Catch-Up | $7,500 |
| After-Tax Room | $36,500 |
Who Benefits from the Mega Backdoor Roth Calculator?
This mega backdoor Roth calculator is designed for:
- High-income earners who’ve maxed out regular 401(k) and IRA contributions
- Employees at companies offering after-tax 401(k) contributions
- Anyone seeking to maximize tax-free retirement growth
- Financial planners modeling advanced retirement strategies for clients
Frequently Asked Questions
What is a mega backdoor Roth?
A mega backdoor Roth is a strategy where you make after-tax contributions to a 401(k) plan (beyond the regular employee deferral limit) and then convert or roll them into a Roth account, allowing for substantially larger Roth contributions than the standard IRA or 401(k) Roth limits.
How much can I contribute through a mega backdoor Roth?
Your after-tax contribution room is the overall 415(c) limit (plus catch-up if eligible) minus your employee elective deferrals and any employer contributions already made.
Does my employer plan need to allow this?
Yes. Your 401(k) plan must explicitly allow after-tax contributions and either in-service withdrawals or in-plan Roth conversions for the mega backdoor Roth strategy to work.
Are mega backdoor Roth conversions taxed?
The after-tax contributions themselves are not taxed again upon conversion, but any investment growth that occurred before the conversion may be subject to tax, so converting promptly minimizes any tax owed.
Is my data stored anywhere?
No. All calculations run locally in your browser. No data is sent to any server.
Not all 401(k) plans permit after-tax contributions or mega backdoor Roth conversions. Confirm plan rules with your plan administrator, and verify current IRS limits before acting on these results.