A quick word on the limits, in 2026 numbers. The IRS lets anyone under 50 put $24,500 of their own pay into a 401(k) or the TSP. Hit 50 and you get an $8,000 catch-up on top — $32,500 total. And if you’re 60 to 63, a law called SECURE 2.0 gives you a “super catch-up” of $11,250, for $35,750 all in.
The TSP has a habit of cutting you off: once your contributions hit the year’s limit, they just stop taking the money, so you can’t accidentally go over. That’s the guardrail, and it works. But here’s the nice part about turning 50: instead of the cutoff, the extra just keeps flowing into the catch-up bucket. The TSP calls it the spillover method, and for me it starts in 2031 — my 50th year, even though my birthday is just shy of 1982. Many 401(k) plans have the same spillover feature; if yours doesn’t, you can raise your own election once you’re catch-up eligible.
A 50-year-old can put the full $8,000 catch-up in if they want. Me? I’m not chasing the full $8,000 — it’s optional as far as I’m concerned. I’ll keep my 31.5% right where it is and let whatever spills past the base limit land in the catch-up. Same paycheck deduction, a little extra room, no paperwork.
On the stepped limits — the IRS raises the caps in $500 increments, rounding down — the spill runs $957 in 2031 and about $8,970 in all through 2038. Filling the bucket instead, every dollar of catch-up, would take roughly 40% of my pay and end 2038 at about $5.06 million at a 14% return. So far, I’m not planning to. The option’s there; the plan doesn’t need it.
That’s the whole trick: set the rate once, and let the calendar open the second bucket for you.