What plan features are required for a Mega Backdoor Roth?

Your employer's 401(k) plan must explicitly offer two features: 1) Voluntary after-tax contributions (distinct from Roth 401k), and 2) In-service Roth rollovers or automated daily in-plan Roth conversions.

Are earnings on after-tax 401(k) contributions taxable?

If converted immediately (or via automated plan conversion), growth occurs tax-free inside the Roth. Any earnings accumulated before conversion are taxable as ordinary income in the year of conversion.

USAUpdated for 2026retirement

Mega Backdoor Roth 401(k) Contribution Calculator 2026

Calculate your maximum after-tax non-Roth 401(k) contribution room for execution of a Mega Backdoor Roth strategy up to the statutory $70,000 / $77,500 IRC § 415(c) limit.

Retirement & Pensions Taxes & Duties Investment & Assets Salaries & Monthly Wages

Calculated Result

Maximum Mega Backdoor After-Tax Capacity

$36,500

Calculator Inputs

Your Regular Pre-Tax or Roth 401(k) Deferral

Quick select:

Employer Match & Profit Sharing Contributions

Quick select:

Age 50 or Older ($7,500 Catch-Up Eligible)?

Maximum Mega Backdoor After-Tax Capacity

$36,500

Total Annual Roth Savings Capacity

$60,000

Monthly After-Tax Contribution Target

$3,041.67

Total Statutory IRC § 415(c) Limit

$70,000

The Mega Backdoor Roth requires your employer's 401(k) plan to permit voluntary after-tax contributions and in-service distributions or in-plan Roth conversions (IRC § 402A(c)(4)).

Official Statute: Internal Revenue Code (26 U.S.C. § 415(c) - Annual Additions Limit & In-Plan Roth Rollovers)Last Verified: 2026-09-04

Calculation Methodology

Total 415(c) Plan Limit = $70,000 (plus $7,500 Catch-up if age 50+). Mega Backdoor After-Tax Capacity = max(0, Plan Limit - Regular Employee Deferral ($23,500) - Employer Match & Profit Sharing). Future Tax-Free Value = Compound interest on converted Roth assets.

Frequently Asked Questions

It is an IRS-sanctioned method allowing high-earning employees to contribute after-tax dollars to their employer's 401(k) beyond the standard $23,500 limit up to the $70,000 total limit, and immediately convert those funds to Roth.

Related Calculators

Recommended tools and calculators tailored to your current calculation

Explore all tools

USA

Mega Backdoor Roth 401(k) Contribution Calculator 2026

Calculator Inputs

Calculation Methodology

Frequently Asked Questions

Related Calculators

Solo 401(k) vs SEP IRA Contribution Limits Calculator 2026

Backdoor Roth IRA Pro-Rata Rule Calculator (Form 8606) 2026

US Traditional IRA vs. Roth IRA Tax Savings & Growth Comparison Calculator

US 401(k) Retirement Savings, Employer Match & Growth Calculator

US Flexible Spending Account (FSA) Tax Savings Calculator 2026

US Severance Pay & Separation Package Tax Calculator 2026

US Social Security Disability Insurance (SSDI) Benefit Calculator 2026

US Foreign Earned Income Exclusion Calculator (FEIE Form 2555) 2026