Mega Backdoor Roth Calculator

Calculate max after-tax 401(k) contribution for mega backdoor Roth. 2026 total limit: $72,000.
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Max After-Tax (Mega Backdoor)

$37,500.00

Total Retirement Savings

$72,000.00

Savings Rate

36.00%

415(c) Limit Breakdown

2026 Total 415(c) Limit$72,000.00
Employee Pre-Tax/Roth- $24,500.00
Employer Match- $10,000.00
Available for After-Tax$37,500.00
Your After-Tax Contribution$37,500.00

Mega Backdoor Roth Benefit

Annual Roth Conversion$37,500.00
Tax-Free Growth (10yr @ 7%)$36,268.18
Total Retirement Savings$72,000.00

Use the Mega Backdoor Roth Calculator above to calculate your results. Enter your values and see instant results — all calculations run in your browser.

Disclaimer: This calculator is for informational purposes only and does not constitute tax, financial, or legal advice. Results are estimates based on the information you provide and current rates. Always consult a qualified tax professional or financial advisor for advice specific to your situation.

How It Works

Unlock the power of the Mega Backdoor Roth by calculating your maximum after-tax 401(k) contribution. This calculator helps you determine how much you can contribute beyond the standard limits to grow your retirement savings tax-free, leveraging the 2026 total contribution limit of $72,000.

The calculator determines your maximum after-tax 401(k) contribution by subtracting your pre-tax 401(k) contributions and any employer contributions from the total IRS 401(k) contribution limit for 2026 ($72,000). The remaining amount is your eligible after-tax contribution.

Remember, not all 401(k) plans allow after-tax contributions or in-service distributions for Roth conversions. Always confirm your plan's specific rules with your HR or plan administrator before planning your contributions to avoid common pitfalls.

Example: Maximizing Your Roth Conversion

  1. 1 Input your 2026 pre-tax 401(k) contributions (e.g., $23,000) and your employer's 401(k) contributions (e.g., $10,000).
  2. 2 The calculator subtracts these amounts from the 2026 total 401(k) limit of $72,000: $72,000 - $23,000 - $10,000.
  3. 3 Your maximum after-tax 401(k) contribution for a Mega Backdoor Roth is $39,000.
  4. 4 This $39,000 can then be converted to a Roth account, allowing for tax-free growth and withdrawals in retirement, assuming your plan facilitates these conversions.

Source: IRS · Last updated: April 2026

Frequently Asked Questions

What is the mega backdoor Roth?
The mega backdoor Roth lets you contribute after-tax dollars to your 401(k) beyond the $24,500 employee limit, then convert those to a Roth account. The total 401(k) limit is $72,000 in 2026, so you can potentially convert up to $47,500 beyond the standard deferral (minus employer match).
Does my employer 401(k) allow the mega backdoor Roth?
Not all plans do. Your 401(k) must allow after-tax contributions (different from Roth contributions) and permit either in-plan Roth conversions or in-service distributions. Check with your HR department or plan administrator. About 30-40% of large employer plans support this strategy.
How much can I contribute through the mega backdoor Roth in 2026?
The maximum is $72,000 total minus your employee deferral ($24,500) minus employer match contributions. If your employer matches $8,000, you can contribute up to $39,500 in after-tax dollars for conversion. Add the catch-up contribution if age 50+ for $79,500 total.

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