Your 401(k) Catch-Up Contributions Are Now Forced Into Roth. Here’s What That Changes.

A rule that took effect January 1 is reshaping how millions of workers over 50 contribute to their 401(k) — and most of them haven’t noticed it yet.

If you earned $150,000 or more in 2025, every catch-up contribution you make to your 401(k) this year must go into a Roth account. Not pre-tax. Not your choice. Roth. That’s the SECURE 2.0 Act, Section 603, now in force. The income threshold is technically $145,000, indexed for inflation — for the 2026 tax year, it lands at $150,000, based on your 2025 W-2 wages from the employer sponsoring your plan.

Here are the numbers. The base 401(k) contribution limit for 2026 is $24,500, up from $23,500 last year. If you’re 50 or older, you’re eligible for a catch-up contribution of $8,000 on top, bringing your annual maximum to $32,500. If you’re between 60 and 63, the SECURE 2.0 super catch-up raises that extra amount to $11,250 instead, for a total ceiling of $35,750. Those are significant numbers. The rule change is about where those catch-up dollars must go.

Before 2026, the treatment was flexible. You could contribute catch-up dollars on a pre-tax basis — reducing your taxable income now and deferring taxes until retirement. Above the $150,000 threshold, that option is gone. The money goes in after-tax, grows tax-free inside the Roth account, and comes out tax-free at retirement. For many high earners, that turns out to be a better deal than it first appears. If you’ve been earning $150,000+ for years, your retirement income will likely be substantial: required minimum distributions, Social Security, dividends, rental income. Your retirement tax rate may be equal to or higher than what you pay today. Paying tax now, at a known rate, beats paying it at an unknown rate in 25 years. Roth also sidesteps Medicare’s IRMAA surcharges, which kick in at $109,000 MAGI for single filers and $218,000 for married couples filing jointly — surcharges that quietly inflate Part B and Part D premiums and are nearly impossible to undo once triggered.

But there is a trap that will catch a meaningful number of workers this year. If your employer’s 401(k) plan does not offer a designated Roth account, you cannot make catch-up contributions at all. Not pre-tax. Not Roth. Zero. The IRS has no workaround for this: if there is no Roth bucket in your plan to receive the money, the contribution cannot be made. Call HR today. Ask specifically whether your plan offers a designated Roth 401(k) option. If the answer is no, confirm when the plan sponsor expects to add one — employers have until 2027 to achieve full compliance, but that deadline does not help your 2026 contributions.

What this rule means for your specific retirement balance depends on your tax bracket now, your projected income in retirement, and when you plan to stop working. The tax treatment of $8,000 a year for ten years at 7% annual growth looks very different if your effective retirement rate lands at 15% versus 28%. The Retirement Calculator runs that comparison in under two minutes. Enter your current balance, set your annual contribution to $32,500 or $35,750, use a 7% return, and project to your target retirement age. Then think through the after-tax value at withdrawal — the full Roth balance is yours, untaxed. The pre-tax equivalent requires a tax haircut on every dollar you take out.

Put real numbers on the two futures. An $8,000 catch-up contribution made pre-tax by a worker in the 24% bracket saves $1,920 in taxes today; made as a Roth contribution under the new rule, that $1,920 is paid now — and in exchange, every dollar of growth comes out untaxed. Left to compound at 7% for ten years, the $8,000 becomes roughly $15,700. Withdrawn from a pre-tax account at a 22% retirement rate, that money nets about $12,250. From the Roth: the full $15,700. The mandate forces the choice, but for workers who expect their tax rate to hold steady or rise, it forces them into the better half of the trade.

The genuine losers are those who expect a steep bracket drop in retirement — the executive earning $200,000 today who will live on $60,000 later. For them, the lost deduction is a real cost, and the response worth discussing with a planner is rebalancing where other dollars go: the base $24,500 can still be contributed pre-tax, and outside the plan, deductible HSA contributions and timing of other income can claw back some of what Section 603 took.

Two administrative checks are worth making this week. First, confirm which wage number your plan is using — the $150,000 test is based on last year's W-2 from this employer, so a new hire who earned their 2025 wages elsewhere may not be caught by it at all. Second, ask whether your plan actually offers a Roth catch-up option. Plans that never added a Roth feature had to build one for this rule; if yours is behind, affected employees can temporarily lose access to catch-up space entirely — a conversation to have with HR before the December payroll cutoff, not after it.

If your plan offers Roth and you’re above the threshold, verify your contribution elections now. Most payroll systems don’t auto-switch existing pre-tax catch-up elections to Roth — you may need to update them manually. If you’re unsure whether the switch happened, check your most recent pay stub: Roth contributions appear as after-tax deductions, not pre-tax deferrals. The distinction matters at every paycheck between now and December 31. Run your actual numbers in the Retirement Calculator — not a generic projection, your numbers — and see what the forced switch means for your retirement balance.