⚡ Interactive Tax-Optimization Tool

Mega Backdoor Roth Contribution Calculator

Determine your exact remaining after-tax 401(k) space for a Mega Backdoor Roth conversion after accounting for employee deferrals, employer matches, and IRS compensation limits.

🧮 Enter Your 401(k) Plan Details

Updated with official IRS 2026 contribution limits (Section 415(c) & Section 401(a)(17)).

2026 IRS Cap: $355k
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IRS Rule: Under IRC Section 401(a)(17), 2026 employer matches are capped at compensation up to $355,000.

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Standard 2026 employee elective deferral (Traditional 401(k) + Roth 401(k) combined).

Employer Match Formula
%
%
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Your 401(k) Breakdown Total Cap: $71,000
Available After-Tax Contribution Room
$41,600
Eligible for Mega Backdoor Roth Conversion
IRS Overall Limit (Sec. 415c): $71,000
(-) Employee Deferral: -$24,000
(-) Employer Match: 50% on first 6% of $180,000
-$5,400
(=) Remaining Mega Backdoor Space: $41,600
Per-Paycheck Allocation
Bi-Weekly (26/yr) $1,600.00
Semi-Monthly (24/yr) $1,733.33
Follow Step-by-Step Setup Guide

How the 2026 Mega Backdoor Roth Contribution Limits Work

The Mega Backdoor Roth strategy allows high-income earners to exceed the standard $24,000 elective deferral limit and contribute up to the total IRS Section 415(c) limit ($71,000 for under age 50 in 2026) into tax-free Roth accounts.

The Mega Backdoor Contribution Formula:

After-Tax 401(k) Space = 2026 IRS Section 415(c) Total Limit ($71,000) - Employee Elective Deferrals - Employer Matching Contributions

🏛️ IRS Section 401(a)(17) Salary Cap

Even if your compensation is $500,000, federal law caps the maximum salary recognized for 401(k) matching at $355,000 in 2026. Any percentage match formula only calculates up to this ceiling.

🔄 Automatic In-Plan Conversions

After making voluntary after-tax contributions, you must immediately convert them to a Roth 401(k) or Roth IRA. Doing this automatically prevents earnings from growing in a taxable pre-tax bucket.

Recommended Guides & Next Steps

Step-by-Step Guide Fidelity Mega Backdoor Roth Walkthrough → Standard Backdoor Backdoor Roth IRA with Fidelity → Index Funds Recommended Low-Cost Index Funds →
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