The 8-month rule
If you delay Part B because of group health coverage based on your (or your spouse's) current employment, you can sign up during a Special Enrollment Period (SEP). The SEP lasts while you have that coverage and for 8 months after the employment or the coverage ends, whichever comes first. No late penalty applies.
What counts and what does not
| Coverage | Counts for the SEP? |
|---|---|
| Group plan from your own current job | Yes |
| Group plan from your spouse's current job | Yes |
| COBRA | No |
| Retiree coverage | No |
| ACA Marketplace plan | No |
| Coverage from a job you have already left | No |
Employer size matters
If the employer has 20 or more employees, the employer plan generally pays first and Medicare second, so delaying Part B is common. If the employer has fewer than 20 employees, Medicare generally pays first, so skipping Part B can leave you with large unpaid bills. Ask your benefits office which applies to you.
How to sign up
- Complete the Part B application (Form CMS-40B).
- Have your employer complete Form CMS-L564 to confirm your coverage dates.
- Send both to Social Security (online, by phone at 1-800-772-1213, or at an office).
Other Special Enrollment Periods
Other life events can open a window to change or join a plan, such as moving out of your plan's service area, losing other coverage, or changes in Medicaid or Extra Help status. Part D has its own rule: going 63 days or more without creditable drug coverage can lead to a permanent late penalty.