Mega Backdoor Roth Projection Calculator

Project Mega Backdoor Roth growth over time. Compare Roth conversion vs keeping after-tax 401k. See tax savings.

Must exceed 401k contribution limit ($23k in 2024)

Employer match on regular 401k (not Mega Backdoor)

After-tax 401k contributions (max $46.5k total with employer in 2024)

Expected return on 401k investments

Immediate conversion avoids taxes on gains

Only if converting to Roth immediately

Annual Mega = $69k (2024 limit) - $23k (regular 401k) - Employer Match. Future Value = Σ(Annual × (1+r)^years). Roth: tax-free growth. After-tax: gains taxed at withdrawal.
Age 30 to 65 (35 years), $2,000/month ($24k/year) Mega Backdoor, 8% return, convert to Roth: Balance = $3,723,456. Without Roth conversion: ~$3,165,938 (after future taxes). Savings: $557,518.

What is the Mega Backdoor Roth?

Mega Backdoor Roth allows contributing extra to 401k (after-tax, not Roth) and immediately converting to Roth IRA. 2024 limit: $69,000 total (employee + employer) minus regular contributions ($23k). High earners can put $30k+ into Roth tax-free growth. Requires plan to allow after-tax contributions + in-service withdrawals/conversions.

How much can I contribute to Mega Backdoor?

2024 limit: $69,000 total 401k (employer + employee). Subtract: regular 401k ($23k under 50, $30.5k 50+), employer match (e.g., 5% of salary). Remaining is Mega Backdoor capacity. Example: $150k salary, 5% match = $7.5k. $69k - $23k - $7.5k = $38.5k Mega Backdoor capacity.

Why convert to Roth immediately?

After-tax 401k contributions are NOT taxed, but GAINS are taxed as ordinary income when withdrawn. By converting immediately to Roth, gains grow tax-free. Without conversion, you'll owe taxes on decades of growth. Some plans auto-convert; others require manual in-service withdrawal.

What are the tax implications?

Conversion taxes: Regular contributions already taxed (after-tax). Earnings converted to Roth are taxed at ordinary income rates. However, future growth is TAX-FREE. Pay $2k in taxes now on $20k conversion to save $40k+ in future taxes. Roth withdrawals in retirement are completely tax-free (contributions + gains).