The 8-month window
Your Part B Special Enrollment Period (SEP) begins the month after your employer coverage ends or the month after your employment ends — whichever comes first. You have 8 months from that date to enroll.
Important: The 8-month clock starts when coverage OR employment ends — not when you decide to enroll. Don't wait until you need care to sign up.
How to enroll during your SEP
You'll need two things:
- Form CMS-L564 — "Request for Employment Information." Your employer fills out this form to verify you had group health coverage based on current employment.
- Application for Medicare Part B — You can apply online at ssa.gov, by phone at 1-800-772-1213, or at your nearest Social Security office.
What if you miss the 8-month window?
If you miss your SEP, you'll face two consequences:
- Waiting period: You'll have to wait for the General Enrollment Period (January 1 – March 31), with coverage starting July 1.
- Late penalty: A permanent 10% increase in your Part B premium for every 12 months you could have had Part B but didn't. At $202.90/month, each year of delay adds about $20.29/month — for life.
Part B SEP vs. Part D SEP
Your Part D enrollment window is different. When employer drug coverage ends, you have just 2 months to enroll in a Part D plan — not 8 months like Part B. Don't confuse the two timelines.