Medicare Enrollment Periods
Identify which enrollment window applies before a deadline or penalty becomes the problem.
Initial Enrollment Period for Part A and B
Most people turning 65 can enroll during the seven-month window that begins three months before the birthday month and ends three months after. The month of application can change when Part B starts. Receiving Social Security benefits may cause automatic enrollment; others must apply through SSA. The enrollment window for a private plan is separate from the underlying A/B effective dates.
Official source: Medicare: When to sign up ↗ · Medicare: When coverage starts ↗ · Medicare: How to sign up ↗
Current-employment Special Enrollment Period
If qualifying coverage is based on your or your spouse’s current employment, you may sign up for Part B while still covered or within eight months after the employment or coverage ends, whichever happens first. Retiree coverage and COBRA do not continue this period. Get the employer evidence SSA requests and verify your coverage start so you do not create a gap. ESRD and other exceptional situations can follow different rules.
Official source: Medicare: When coverage starts ↗ · Medicare: COBRA coverage ↗ · SSA: Sign up for Part B only ↗
General Enrollment Period and penalties
If you missed initial and special enrollment opportunities, the Part B General Enrollment Period generally runs January 1 through March 31, with coverage starting the following month. A Part B late-enrollment penalty may apply, usually 10% for each full 12-month period of avoidable delay, and may persist as long as you have Part B. SSA determines the actual dates and premium.
Official source: Medicare: When to sign up ↗ · Medicare: Avoid penalties ↗ · SSA: Sign up for Medicare ↗
Plan elections in fall
October 15 through December 7 is the annual Medicare Open Enrollment period for Advantage and Part D elections, generally effective January 1. It does not create a new universal Part B Initial Enrollment Period or reset a federal Medigap open-enrollment window. Check the coming year’s drug list, provider directory, Evidence of Coverage and Annual Notice of Change before changing a plan.
Official source: Medicare: Joining a plan ↗ · Medicare: Medicare Advantage guide ↗
Advantage changes after January 1
A person already in Medicare Advantage can generally use the Medicare Advantage Open Enrollment Period from January 1 through March 31 to make one change to another Advantage plan or return to Original Medicare, with a Part D enrollment as allowed. Other life events can create special election periods. The action permitted and effective date depend on the particular window; document both before submitting a change.
Official source: Medicare: Joining a plan ↗