Mega Backdoor Roth Calculator

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

By Konstantin Iakovlev · Updated April 2026 · Source: IRS

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Plan Allows After-Tax + In-Plan Roth Conversion?
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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

The mega backdoor Roth strategy lets high savers push after-tax dollars into a 401(k) well past the usual elective limits, then move that money into Roth territory where it grows tax-free. The headroom available to you in 2026 hinges on the total contribution limit of $72,000 and how much of it your other contributions already consume.

Your maximum after-tax 401(k) contribution comes from one subtraction: take the total IRS 401(k) contribution limit for 2026 ($72,000), then remove your pre-tax 401(k) contributions and any employer contributions. Whatever is left is the after-tax amount you are eligible to put in.

Not every 401(k) plan permits after-tax contributions or the in-service distributions needed for Roth conversions, so the math here only works if your plan does. Check the specific rules with your HR department or plan administrator before you commit to a contribution figure.

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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