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Mega Backdoor Roth

Mega Backdoor Roth Calculator

Unlock after-tax 401(k) contributions and in-plan Roth conversions — up to $46,500 extra per year.

Your Plan Features
Your Situation
Your Mega Backdoor Capacity (2025 Limits)
Total 401(k) limit$70,000
− Your pre-tax/Roth contribution−$23,500
− Employer match−$10,000
= Available after-tax space$36,500
⚠️ Your plan does not support all the features needed for the mega backdoor. Check with your HR/plan administrator about enabling after-tax contributions and in-plan conversions.
Additional Tax-Free Retirement Savings
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from mega backdoor contributions alone, after 25 years
Extra Saved Annually
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Lifetime Contributions
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Tax-Free Growth
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Effective Roth Max
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Mega Backdoor Balance Growth
The mega backdoor turns a standard $7,000 Roth limit into up to $46,500/yr of Roth-equivalent savings. It's the single biggest legal tax-advantaged opportunity for high earners with the right plan features.
2025 total DC plan limit: $70,000 ($77,500 age 50+). Requires specific plan provisions. Not tax advice. Predictable Income

Mega Backdoor Roth Calculator

The Mega Backdoor Roth Calculator quantifies what is arguably the single biggest legal tax-advantaged savings opportunity available to high earners with the right 401(k) plan features. Two checkboxes at the top gate the entire calculation: your plan must allow after-tax contributions and in-plan Roth conversions or in-service rollovers. Enter your salary, age, current pre-tax contribution, and employer match, and the calculator builds a capacity waterfall showing how the 2025 total defined-contribution limit of $70,000 gets carved up, revealing exactly how much after-tax space you have left to fill. The results project the lifetime tax-free balance this strategy generates, your effective annual Roth contribution ceiling (up to roughly $53,500 when combined with a regular Roth), and the tax-free growth your account will produce. When plan features aren't enabled, a warning banner prompts you to ask HR about unlocking them. It's the calculator that turns an obscure, underutilized loophole into a concrete number you can act on.