Which Medicare Enrollment Window Applies?

Which enrollment window am I in?

Medicare does not have one open season for every change. The window depends on whether you are new, already enrolled, leaving a job, or trying to change a Supplement.

By Alan Blackwell, Licensed Medicare Insurance Agent 0M71640. Published September 26, 2026. Updated September 26, 2026.

New to Medicare

The Initial Enrollment Period is seven months around the month you turn 65, or around the month you first become eligible. That is not the same as the fall window. The turning 65 timeline walks through it month by month. The eligibility date tool uses the date you enter. It is not a determination from Social Security.

Already on Medicare

Annual Enrollment is October 15–December 7. The dates and what you can change are on the 2027 Annual Enrollment page. If you are in a Medicare Advantage plan on January 1, Medicare Advantage Open Enrollment runs January 1 through March 31 and allows one change. What to check before October 15 is the preparation.

A job, a move, or a Supplement

Losing employer coverage can open a Special Enrollment Period. COBRA usually does not extend it. Read still working at 65 before you delay Part B. A Supplement follows different rules. In California, the Birthday Rule is for people who already have Medigap. Other Special Enrollment Periods depend on facts this page cannot see.

Let the worksheet sort the dates

The enrollment window tool asks whether you already have Medicare, whether you have Medicare Advantage or a Medicare Supplement (also called Medigap), and whether a Special Enrollment situation applies. It lists Initial Enrollment, General Enrollment, Annual Enrollment, Medicare Advantage Open Enrollment, Medigap Open Enrollment, the California Birthday Rule, and Special Enrollment Periods for a job, a move, Extra Help or Medi-Cal, a plan that is ending, a trial right, an institution, and a 5-star plan. Confirm the one that fits on Medicare.gov or with Social Security.

Common questions

I am turning 65 in November. Do I wait for October 15?

Not necessarily. Your Initial Enrollment Period is tied to your 65th birthday, or to the month you first become eligible. October 15 is the yearly window for people who already have Medicare.

Why does the worksheet ask about a spouse’s job coverage?

Coverage from a current employer, including a spouse’s employer, can change whether you may delay Part B. The size of the employer and the type of coverage matter. Confirm that with the employer and with Social Security.