Guide · updated 2026-08-03
Why COBRA Does Not Protect You From the Part B Penalty
COBRA continues your employer health plan, so it feels like unbroken coverage. For Medicare's enrollment rules it is not treated as coverage from current employment, which means it does not open a penalty-free special enrollment period. This is one of the most expensive misunderstandings in the whole system.
The special enrollment period depends on CURRENT employment
The rule that lets someone delay Part B past 65 without a penalty is tied to group health coverage based on current employment — yours or a spouse's. The word doing the work is current. COBRA continues a plan after that employment has ended, so however identical the card in your wallet looks, the qualifying condition has already stopped being met. The special enrollment period generally runs for eight months from the end of the employment, not from the end of COBRA.
Two clocks run at once and they do not run together
This is what makes the trap so effective. COBRA typically lasts eighteen months, and the special enrollment period for Part B is eight. Someone who takes COBRA at retirement and enrolls in Medicare when it runs out has, in the ordinary case, missed the window by ten months — and by then the next opportunity is the general enrollment period, with coverage starting later and a permanent penalty attached. Nothing in the COBRA paperwork points this out, because COBRA administrators are not administering Medicare.
COBRA also generally pays second once you are eligible for Medicare
Beyond enrollment timing there is a payment-order problem. For someone eligible for Medicare, COBRA is generally the secondary payer, which means it pays after Medicare would have. If Medicare has not been taken up, the share Medicare would have paid may simply go unpaid rather than falling to COBRA. The result is a person holding what looks like full coverage and carrying a large share of their own bills, which is usually discovered at the worst possible moment.
Retiree coverage sits in the same place
Coverage offered to former employees after retirement is not current-employment coverage either, and it carries the same consequences on both counts: no penalty-free special enrollment period for Part B, and generally secondary payment once Medicare eligibility begins. If a benefits office says the plan works with Medicare, the question worth asking in writing is whether it pays first or second, and whether it is expected to be creditable for drug coverage.
Official sources for this guide
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