Made $150,000 last year? Your 401(k) catch-up is Roth now.

Congress put this in the SECURE 2.0 Act back in 2022. Treasury and the IRS finalized the regulations on September 15, 2025 (IR-2025-91). The mechanic is simple: if your prior-year Social Security wages from the employer that sponsors your plan cleared a threshold, your catch-up contributions have to be designated Roth. IRS Notice 2025-67 set that threshold at $150,000 of 2025 wages, raised from the $145,000 written into the original statute.

Two things it does not touch. Your base deferral is unaffected: $24,500 for 2026, still your choice of pre-tax or Roth. And the catch-up amounts did not shrink. It is $8,000 if you are 50 or older, and $11,250 if you turn 60, 61, 62, or 63 this year. So a 50-year-old can still put away $32,500 and a 61-year-old can still put away $35,750. What changed is the tax treatment of the last slice, not the size of it.

Price it. Say you are single, 52, earning $180,000. After the 2026 standard deduction of $16,100 your taxable income sits inside the 24% bracket, which runs from $105,700 to $201,775 for single filers this year. Eight thousand dollars of pre-tax catch-up would have cut your federal tax by $1,920. Roth means you write that $1,920 now instead. If you are 60 to 63 and putting in $11,250, the same math comes to $2,700.

That is the entire cost, and it is a timing shift, not a penalty. You prepay tax on money that then grows and comes out tax-free. Whether you come out ahead turns on one comparison: your marginal rate today against your marginal rate when you withdraw. Peak earner in the 32% bracket who expects to retire into the 22%? Being forced into Roth is a mild loss. Already sitting on a pre-tax balance big enough that required minimum distributions will shove you into a higher bracket at 73? It is a win. And since 2024, Roth 401(k) money has no required minimum distributions during your lifetime, which is a genuine consolation prize rather than a rounding error.

If your plan does not permit Roth deferrals, affected employees cannot make catch-up contributions at all. There is no pre-tax fallback. The plan cannot quietly route the money the old way, so the $8,000 you assumed was going in simply does not go in, and you find out in January when you look at the total.

There is a second wrinkle worth knowing. The final regulations technically apply to tax years beginning after December 31, 2026, but the IRS allows plans to implement the requirement for earlier years using a reasonable, good-faith interpretation. That means how your specific plan is handling 2026 is a real question with a real answer, and only your plan can tell you. Call the provider or open the plan document and look for two things: whether designated Roth contributions are offered, and how catch-up elections are being coded this year.

The test runs per employer, on prior-year wages, which creates a few clean exits. Started a new job in 2026? That employer paid you nothing in 2025, so there are no prior-year wages to test and your catch-up there can go in pre-tax. Same logic covers a partner or owner drawing only self-employment income with no W-2 wages: no FICA wages, no Roth requirement.

And if your 2025 wages came in under $150,000, nothing about your 401(k) changed. Pre-tax catch-up is still yours. The threshold is indexed to inflation, though, so it moves, and a raise can walk you across it without anyone mentioning it. If you are within shouting distance of the line, make checking it a January habit.