The total 2026 401(k) limit is $70,000 (under age 50). This includes three types of contributions:
- Employee pre-tax or Roth deferrals: up to $23,500
- Employer match: varies by employer
- After-tax contributions: fills the remaining space up to $70,000
Example: You contribute $23,500 pre-tax. Your employer matches $6,000. That is $29,500 used. You have $40,500 of after-tax space remaining. You contribute $40,500 after-tax, then immediately convert it to Roth. That $40,500 now grows tax-free forever.
The mega backdoor Roth is the conversion step — turning after-tax 401(k) money into Roth money.