COBRA and Medicare: The Trap Hiding in the 8-Month Clock

How the trap plays out

Say you retire at 66 and take COBRA for 18 months because it keeps your familiar plan. Your Part B Special Enrollment Period ends 8 months after you stopped working. Months 9 through 18 feel fine; COBRA is paying claims. Then COBRA ends, and you discover:

• Losing COBRA does not give you a new enrollment window. Medicare.gov lists it explicitly among the situations that do not qualify for a Special Enrollment Period.
• You wait for the General Enrollment Period (January 1 to March 31), with coverage starting the month after you sign up, a gap that can run the better part of a year.
• You may owe the Part B late enrollment penalty: an extra 10% of the premium for each full 12-month period you could have had Part B but didn't, added to your premium for as long as you have Part B. At 2026 rates, a 20% penalty means paying $243.50 instead of $202.90, every month, for life.

The right order of operations at 65

If you're 65 or older and your job (or your spouse's job) is ending, the safe sequence is:

• Enroll in Part B during the 8 months after employment ends, ideally before the group coverage stops, so there's no gap. If you already have Part A, you can add Part B online at SSA.gov.
• Then decide what rides alongside: COBRA can still make sense as secondary coverage for a spouse under 65 or to finish a treatment year, but for you, once you're Medicare-eligible, Medicare should be in place first.
• Mind drug coverage too. Going 63 or more days without creditable drug coverage triggers Part D's own late penalty (1% of the national base premium per month, permanently). If your COBRA drug coverage isn't creditable, the Part D clock is also running.

Working past 65 is the one real exception

The 8-month Special Enrollment Period exists because active employer coverage (from a current job, yours or your spouse's, generally at an employer with 20+ employees) genuinely lets you delay Part B without penalty. The distinction Medicare draws is active employment versus everything after it: the day the job ends, COBRA and retiree coverage stop counting, and the 8 months begin.

The California consolation prize

One state-level bright spot: under California Insurance Code § 10192.11(e), when your COBRA or Cal-COBRA coverage ends, you get a 6-month open enrollment window for Medigap: insurers can't deny you or price you up for health history. So if you land in the trap, the path back to solid coverage (Part B at GEP + a guaranteed-issue Medigap) exists; it's the gap and the lifetime penalty you can't undo. Once you're in, California also runs an annual Medigap switching window: the birthday rule.