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.
Updated with official IRS 2026 contribution limits (Section 415(c) & Section 401(a)(17)).
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.
After-Tax 401(k) Space = 2026 IRS Section 415(c) Total Limit ($71,000) - Employee Elective Deferrals - Employer Matching Contributions
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.
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.