Mega Backdoor Roth After-Tax 401(k)
Mega backdoor Roth uses after-tax 401(k) contributions ($46K+ above standard $23K limit), then in-service Roth conversion. Limited by plan + 2026 $70K total cap.
| Elective deferrals (Trad+Roth) | — |
| Employer match | — |
| 2026 total cap | — |
| Catch-up (50+) | — |
| After-tax 401k room | — |
| Total 401k contribution | — |
Mega backdoor Roth maximizes 401(k) contributions to the IRS Section 415 limit ($70,000 for 2026 estimated, $77,500 with catch-up). Employee deferrals + employer match + after-tax contributions all count.
Section 415 Total Limit
2026 estimated $70K (was $69K 2024). Includes all contributions: pre-tax + Roth + match + after-tax + forfeitures. Catch-up adds $7,500 for 50+. Total potential $77,500 for senior earners.
Plan Requirements
Mega backdoor requires plan to allow: (1) after-tax non-Roth contributions beyond elective deferral, (2) in-service Roth in-plan conversion OR in-service rollover to Roth IRA. Many plans don't allow #2 — check first.
Why It Beats Standard Backdoor
Standard backdoor Roth IRA capped at $7K/year. Mega backdoor allows $46K+ AFTER tax (then convert to Roth). 6.5× the contribution power. Critical for high earners maximizing tax-advantaged space.
HCE Discrimination Testing
Highly Compensated Employee testing (ADP/ACP) may cap after-tax for HCEs. Plans with safe harbor design or high overall participation rate often allow full $46K mega backdoor without issue.
Last updated May 2026. Sources: IRS 415 Limits, IRC §415(c).