Employer coverage after 65: who pays first and when to sign up for Part B
The 20-employee rule, how primary and secondary payers work, and when delaying Part B is safe because of creditable job-based coverage.
If you keep working past 65, your job's health plan and Medicare may work together. The size of the employer decides who pays first.
| Your situation | Who pays first | Part B needed at 65? |
|---|---|---|
| Active job, employer with 20+ workers | Employer plan | Usually can delay without penalty |
| Active job, employer with fewer than 20 workers | Medicare | Yes, usually required |
| Retiree coverage | Medicare | Yes |
| COBRA | Medicare | Yes; COBRA does not prevent the penalty |
| Spouse's active job, 20+ workers | Employer plan | Usually can delay |
Delaying Part B safely
If your coverage is based on current employment at an employer with 20 or more workers, you can delay Part B. When the job or coverage ends, you have an 8-month Special Enrollment Period. Use form CMS-40B with CMS-L564 completed by the employer. Miss it and you face a lifetime penalty.
Part A while working
Most people take premium-free Part A at 65 even while working. But if you contribute to an HSA, see HSAs and Medicare first.
Compare costs
Sometimes Medicare plus a Medigap plan costs less than staying on an expensive employer plan, especially for a spouse. Compare the full premium and deductible. In Washington and Florida, Maru Insurance can compare Medicare options against your employer plan.
Questions people ask
Can I delay Part B if I'm working?
Usually yes, if the employer has 20+ workers and coverage is from current employment.
Does COBRA count?
No. COBRA does not let you delay Part B without penalty.
How long is the Special Enrollment Period?
Eight months after employment or coverage ends.
Who pays first at a small employer?
Medicare, for employers with fewer than 20 workers.
Independent educational site. Not affiliated with or endorsed by the U.S. government, the federal Medicare program, or any insurance company. Figures are 2026 amounts published by CMS unless noted; check Medicare.gov for your situation.