Still working at 65: do you need Part B?
If you (or your spouse) are still working and covered by that employer's group health plan, you can usually delay Part B without a penalty when the employer has 20 or more employees. If the employer has fewer than 20, Medicare generally pays first, and you'll usually want Part A and Part B when you're first eligible.
By Nick Heyse, independent licensed insurance agent (NPN 20605586) · Last reviewed October 2026
The employer-size rule
| Your job-based coverage | Who pays first | Part B usually |
|---|---|---|
| Employer with 20 or more employees | The employer plan | Can be delayed without penalty |
| Employer with fewer than 20 employees | Medicare | Enroll when first eligible |
| COBRA or retiree coverage | Medicare | Enroll — this doesn't count as current employment |
The coverage has to be based on current employment — yours or your spouse's. That's the detail people miss most often with COBRA and retiree plans.
When the job coverage ends
You get a Special Enrollment Period of 8 months to sign up for Part B without a penalty, starting the month after the employment or the coverage ends, whichever comes first. Don't wait for the end of it — a gap in coverage can still happen.
Social Security will ask for two forms: CMS-40B (the Part B application) and CMS-L564, which your employer fills in to show you had coverage.
Part A, drugs and HSAs
- Part A: most people pay no premium for it, so many take it at 65 even while working — unless they're contributing to an HSA.
- HSA: once you have any part of Medicare you can't keep contributing, and Part A can start up to six months back. Plan the timing with your tax advisor.
- Drug coverage: ask HR for the notice that says whether your drug coverage is "creditable." If it is, you can delay Part D without a penalty.
Your Medigap window waits for Part B
Your six-month Medigap Open Enrollment Period starts when Part B starts. Delaying Part B also delays that window, which matters in Kansas, where there's no second chance without health questions.
Check it yourself: the official sources are Medicare.gov and 1-800-MEDICARE (TTY 1-877-486-2048).
1-800-MEDICARE is available 24 hours a day, 7 days a week.
Not sure what applies to your job coverage?
Thirty minutes, free, and no obligation to enroll in anything. Phone, video, or in person around Kansas City.