How much would you save in lifetime taxes with Mega Backdoor Roth?

If you're already maxing your 401(k) and Roth IRA, your next dollar of savings goes to a regular brokerage — and pays dividend tax every year plus capital gains tax at withdrawal. Mega Backdoor Roth shelters those same dollars instead. See what that's worth.

First — does your plan support this?

Three quick questions. Takes 30 seconds.

1. Does your 401(k) plan allow after-tax (non-Roth) contributions?

Yes

Not sure

2. Does it allow in-plan Roth conversions or in-service withdrawals?

Yes

Not sure

3. Are you already maxing your regular 401(k) ($23,500 / $31,000 if 50+) and Roth IRA ($7,000 / $8,000 if 50+)?

Yes

Tell us about your situation

Defaults are set for a typical high-earner case. Adjust as you'd like.

Current age

Retirement age

Annual mega backdoor contribution (after-tax 401k → Roth)

Current retirement balance (401k + IRA + Roth combined)

Household income

Filing status

Target annual retirement spending

Plan-to age

Routing this contribution to Roth instead of a regular brokerage saves you

in lifetime taxes — that's why mega backdoor matters.

Lifetime tax saved

Dividend tax during accumulation + LTCG at withdrawal

Annual spending power delta

$0/yr

Extra sustainable spending in retirement

Cumulative extra spending

Over your full retirement

Investable assets over time, at your target lifestyle

Both lines spend the same lifestyle amount each year in retirement. The gap is the tax drag of the taxable path.

How we calculated this

Comparison: baseline routes the same dollar amount to a regular taxable brokerage (the realistic alternative for someone already maxing pre-tax 401(k) and Roth IRA). Modified routes it to Roth via mega backdoor. The delta is the tax-treatment difference, not the contribution itself.
Lifetime tax saved = annual dividend tax during accumulation + LTCG tax at withdrawal that you'd pay on the taxable path but avoid in the Roth path. Assumes 2% qualified dividend yield, 18% effective dividend tax, 15% LTCG rate, 60% gain fraction at withdrawal.
Returns: 6.5% real return on tax-advantaged accounts, 5.8% on taxable (after dividend tax drag).
Pre-tax tax rate at withdrawal: flat 22% effective rate (federal + state + IRMAA approximation; 24% for HHI ≥ $400K).
Withdrawal sequence: taxable first, then pre-tax (Traditional 401k/IRA), then Roth.
Existing balance composition: assumed 70% pre-tax / 20% Roth / 10% taxable.
Not modeled: Social Security, IRMAA tier dynamics, ACA bridge years, RMDs, state-by-state tax variation, sequence-of-returns risk. The precise number depends on these — book an Assessment for your numbers.

How much would you save in lifetime taxes with Mega Backdoor Roth?

First — does your plan support this?

Tell us about your situation

Investable assets over time, at your target lifestyle

Get your real numbers