Mega Backdoor Roth Contribution Calculator – After-Tax 401(k) & Section 415(c) Limit

Calculate the exact after-tax headroom available in your employer 401(k) for Mega Backdoor Roth conversions under IRS Section 415(c) overall annual contribution caps.

Your Regular Elective 401(k) Contributions ($)

Total Employer Match & Profit Sharing ($)

Participant Age (Years)

Does Your 401(k) Permit After-Tax Non-Roth Deferrals?

Mega Backdoor Roth Headroom

$38,000 / year

Additional after-tax Roth capacity

Total 401(k) Annual Funding

$69,000

Section 415(c) Limit ($69,000)

Mega Backdoor Execution Status:

You have $38,000 available for after-tax contributions and instant in-plan Roth conversion!

The 2 Crucial Plan Requirements: Your company 401(k) MUST support both (1) After-Tax Non-Roth contributions and (2) In-Plan Roth conversions (or automated in-service distributions to a Roth IRA).

Tax and wealth planning estimate based on official 2026 IRS codes and statutory rules. This model does not constitute certified CPA tax preparation, ERISA legal counsel, or fiduciary investment advisory.

What is the Mega Backdoor Roth Strategy?

The Mega Backdoor Roth is the most potent tax-shelter technique available to high-earning corporate employees (especially prevalent at Google, Meta, Microsoft, Apple, and Nvidia). It allows participants to channel up to an additional $35,000 to $45,000 per year into a Roth IRA or Roth 401(k), far beyond the standard $7,000 annual IRA cap.

How the Mathematics Work: IRS Section 415(c)

The IRS maintains two separate annual 401(k) contribution limitations:

Section 402(g) Elective Deferral Limit: Caps regular employee pre-tax and designated Roth contributions at $23,000 ($30,500 if age 50+).
Section 415(c) Overall Defined Contribution Limit: Caps total contributions from all sources (employee elective deferrals + employer match + after-tax employee contributions) at $69,000 ($76,500 if age 50+).

The difference between the overall $69,000 cap and your combined regular deferrals and employer match represents your Mega Backdoor headroom. You deposit post-tax non-Roth funds into your 401(k), then immediately execute an automated in-plan Roth conversion, locking in lifetime tax-free growth.

Frequently asked questions

Can anyone do a Mega Backdoor Roth?

No. Your employer's specific 401(k) plan document must explicitly permit after-tax contributions and either in-plan Roth conversions or in-service non-hardship distributions. Approximately 30% of US corporate plans offer this feature.

Are earnings on after-tax contributions taxed?

If converted immediately upon deposit, there are virtually zero earnings to tax. If after-tax funds sit in the account and generate growth before conversion, the growth is taxable as ordinary income in the year of conversion.

Does the Mega Backdoor trigger the Pro-Rata Rule?

No! Unlike the regular Backdoor Roth IRA (which is subject to the Form 8606 pro-rata rule across all traditional IRA balances), 401(k) after-tax accounts are tracked separately and completely bypass the IRA pro-rata calculation.

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