Part B Special Enrollment Period

An eight-month window, penalty-free

If you put off Part B because you had active employer coverage, Medicare gives you a Special Enrollment Period to enroll without any late-enrollment surcharge. It lasts eight months, and using it is exactly how working past 65 avoids the permanent Part B penalty that would otherwise apply.

When the clock starts

The window begins the month after your active employment ends, or the month after the group coverage based on that employment ends — whichever comes first. You can also enroll while still working, before that clock ever starts. Coverage generally begins the month after you sign up, so a little lead time keeps you continuously covered.

How to use it

You file two forms with Social Security. Form CMS-40B is your application for Part B, and Form CMS-L564 is a Request for Employment Information that your employer or plan completes to verify you had active coverage. Submitting both a month or two before your coverage ends lets Medicare start the day after, with no gap.

What doesn’t count

Only active, employment-based coverage opens this window. COBRA, retiree coverage, and marketplace plans do not — and the moment active employment ends, the eight-month clock is already running, no matter what other coverage you pick up afterward. That’s the detail that most often catches people off guard.