Reviewed September 2026.
Turning 65 while you (or a spouse) still have active employer group health coverage is a timing problem, not an automatic birthday sign-up. Many people take Part A (often premium-free) at 65 and delay Part B while current employment coverage continues (you can also enroll in Part B during that coverage). When the job or the group coverage ends (whichever happens first), an 8-month special enrollment period (SEP) generally starts. Confirm employer-size and whose-job facts with Social Security and Medicare.gov before you skip Part B.
Part B penalty context if you mistime: Part B late-enrollment penalty and LEP basics.
Part A vs Part B while working
| Part | Common pattern at 65 with large-employer coverage | Watch-outs |
|---|---|---|
| Part A | Often enroll when eligible; usually no premium if you paid enough Medicare taxes | Medicare enrollment ends HSA contributions for covered months (including employer deposits). Premium-free Part A can be retroactive up to six months (not before eligibility), so stop HSA contributions before that window |
| Part B | Often delay if employer coverage is creditable for delay rules | Skipping without a valid basis risks Part B LEP |
| Part D / drug | Employer drug plan may be creditable; keep annual notices | Gap of 63+ days without creditable drug coverage can trigger Part D LEP |
| Advantage / Medigap | Usually shop when you take Part B and leave group coverage | Lane compare: Advantage vs Medigap |
COBRA is continuation after job-based coverage ends. It is not identical to active employer coverage for Medicare timing: COBRA health coverage and COBRA vs marketplace SEP.
Worked sketch: retire at 67, Part B SEP
Taylor turns 65 in 2025 on a 200-employee company PPO. Taylor stops HSA contributions, enrolls in premium-free Part A only, and delays Part B while employed. Taylor retires June 15, 2027; group coverage ends June 30, 2027. The 8-month SEP generally starts after employment or group coverage ends, whichever is first. Confirm your enrollment and coverage-start dates with Social Security. Taylor applies for Part B in early June 2027 and requests a July 1, 2027 start so coverage does not gap, then shops Medigap tied to Part B: Medigap basics.
| Step | Taylor’s action |
|---|---|
| 1 | Ask HR whether the group plan is primary/secondary at 65 and whether drug coverage is creditable |
| 2 | Stop HSA contributions before Part A start (including employer deposits), then enroll in Part A if that still fits |
| 3 | Calendar the earlier of job-end and coverage-end for the Part B SEP clock |
| 4 | Apply for Part B via Social Security about a month before group coverage ends; confirm a July 1 start |
| 5 | Compare Advantage vs Original + Medigap + Part D in the same sitting |
Checklist
- Get written answers from HR on employer size, Medicare coordination, and drug creditable coverage.
- Decide Part A timing knowing Medicare enrollment stops HSA contributions for covered months; plan the stop date before any retroactive Part A start.
- Do not drop Part B timing onto COBRA lore without checking SSA rules.
- File Part B while still covered or early in the SEP; aim for a Part B start that meets the group coverage end date; keep confirmation letters.
- Shop Medigap / Advantage / Part D as soon as Part B start dates are known.
- Store creditable-coverage notices each year you delayed Part D.
Educational only. Not Medicare, tax, or employment advice. Employer-size rules and SEP timing are fact-specific; confirm with Social Security, Medicare.gov, HR, and a SHIP counselor.