Mega Backdoor Roth 2027 Calculator — After-Tax 401k

Calculate Mega Backdoor Roth contributions for 2027 — after-tax 401k contributions up to the $69,000 total cap, then in-service Roth conversion for tax-free growth.

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The $69,000 Total 401k Cap

2027 IRS limit on total 401(k) contributions (employee pre-tax + employer match + after-tax): $69,000 ($76,500 if 50+). Mega backdoor uses the gap: total cap minus pre-tax employee ($23,000) minus employer match = available after-tax room. Often $20-40k.

Two Steps

Step 1: Contribute after-tax (NOT Roth) to 401k. Step 2: In-service Roth conversion or in-plan Roth rollover. Some plans auto-convert. Without conversion, after-tax earnings are taxable at withdrawal.

Plan Eligibility

Only ~40% of 401(k) plans allow mega backdoor. Need: (1) after-tax contributions allowed, (2) in-service withdrawals or in-plan Roth conversions, (3) employer doesn't restrict. Ask HR or plan administrator before banking on this strategy.

Source: irs.gov 401(k) contribution limits 2027. Last updated: May 2026.