The rule in plain English
For the 2026 plan year, if your prior-year (2025) Social Security wages at the same employer were more than $150,000, any catch-up contribution you make to a 401(k), 403(b), 457(b), or TSP must go into the designated Roth bucket. Pretax catch-up is no longer an option for you.
The paycheck mechanic
Payroll software splits the contribution. The first $24,500 of 2026 elective deferral can be pretax or Roth (your choice). The catch-up on top must be Roth. If you max at age 55 earning $180,000 and contribute $32,500, your W-2 Box 12 will show code D for $24,500 and code AA (Roth 401(k)) for $8,000.
The three most common mistakes
- New job, new employer. The $150,000 test is per-employer. If you changed jobs mid-2025, the prior-year wages that count are only from the *current* employer. You may be exempt from the Roth catch-up rule at the new place even though your total wages crossed the threshold.
- Plan without Roth option. If your plan doesn't offer a Roth bucket, you simply cannot make a catch-up at all in 2026. This is an administrative failure by the plan, not by you. Push your HR/benefits team.
- Overshooting after a raise. Many people set a dollar amount that hits the limit in December. If you cross $150k mid-2025, the rule flips for 2026 and your January paycheck may deduct more tax than you expect.
Edge cases
- Self-employed with a Solo 401(k): you still follow the rule because it's based on FICA wages, and if you pay yourself W-2 compensation above $150k, the Roth catch-up requirement applies.
- Multiple plans at different employers: each employer runs its own test.
- Spousal issues: the rule is per-individual, not per-household, so spouses are evaluated separately.
Strategy
If you're genuinely in the 24% or 32% bracket and don't believe your retirement rate will be higher, the forced Roth feels expensive today. Two partial fixes: 1) bump up pretax contributions on the first $24,500 to front-load the deduction, and 2) model your total tax picture assuming the catch-up is Roth from day one so January doesn't surprise you.
See our Roth vs Traditional 2026 post for the underlying math.