Medicare Enrollment Periods: Every Window Explained

The windows at a glance

Medicare has several enrollment windows, not one. Two of them sign up for Medicare in the first place; the rest only change coverage you already hold, which is the distinction most people miss.

• Initial Enrollment Period: 7 months around your 65th birthday month. Sign up for Medicare for the first time.
• General Enrollment Period: January 1 to March 31. Sign up if you missed your Initial Enrollment Period.
• Annual Enrollment Period: October 15 to December 7. Change your health or drug coverage for January 1.
• Medicare Advantage Open Enrollment: January 1 to March 31. One change, and only if you are already in a Medicare Advantage plan.
• Special Enrollment Periods: Length varies. Opened by qualifying life events.
• Medigap Open Enrollment: 6 months from when you are 65 and have Part B. Buy a Supplement policy with no health questions.

Your Initial Enrollment Period

This is the 7-month window that gets you onto Medicare: 3 months before the month you turn 65, the month itself, and 3 months after. Inside it you can take Part A and Part B, and also join a Medicare Advantage plan or a stand-alone Part D plan. Timing inside the window matters. Sign up before your birthday month and coverage starts on the first day of it. Sign up later and coverage starts the month after you apply, which is how a gap appears. People who qualify because of a disability, or through end-stage renal disease, have their own timing.

The General Enrollment Period, if you missed out

If you miss your Initial Enrollment Period and no Special Enrollment Period applies, January 1 to March 31 is the fallback. You can take Part A and Part B, coverage starts the month after you sign up, and a late enrollment penalty usually comes with it. Once your Part B coverage begins you get a short window to add a drug plan or a Medicare Advantage plan. What this period is not is a chance to change coverage you already have.

The Annual Enrollment Period, October 15 to December 7

This is the one most people mean by Medicare open enrollment. It is when you can switch between Original Medicare and Medicare Advantage in either direction, change Medicare Advantage plans, or join, drop or switch a standalone Part D plan. Changes you make take effect on January 1. Before it opens, your plan mails you an Annual Notice of Change setting out next year's costs, coverage and drug list, and the Evidence of Coverage has the full detail. Reading the notice is the single most useful thing you can do in the fall, because plans change underneath people who assume nothing has moved.

• Switch between Original Medicare and Medicare Advantage: In either direction.
• Change Medicare Advantage plans: From one plan to another.
• Join, drop or switch a Part D plan: Stand-alone drug coverage.

Medicare Advantage Open Enrollment is a different window

January 1 to March 31 looks like a second chance, and for most people it is not. It applies only to people already enrolled in Medicare Advantage, and it allows exactly one change: move to a different Medicare Advantage plan, or leave for Original Medicare and add a drug plan. The change takes effect the first of the month after the plan receives it. If you are in Original Medicare, you cannot use this period to join a Medicare Advantage plan.

Special Enrollment Periods, the ones people overlook

Life events open windows outside the normal dates, and they are easy to miss because nothing announces them. The best known is job coverage: if you or your spouse have a group health plan from current work, you can delay Part B, and when that job or coverage ends you have 8 months to sign up. COBRA does not extend that window, because it is not coverage from current work. Gaining or losing Extra Help opens one of these windows too.

• You move: Out of your plan's service area, or into or out of a nursing home.
• Medicaid changes: You gain or lose Medicaid, or your subsidy status changes.
• You lose creditable drug coverage: Through no fault of your own.
• Your plan leaves: The plan exits Medicare or stops serving your area.

Medigap has its own clock, and it is unforgiving

A Medicare Supplement policy is not tied to the Annual Enrollment Period at all. Your Medigap Open Enrollment Period runs 6 months from the first month you are both 65 or older and enrolled in Part B. Inside it, an insurer must sell you any policy it offers and cannot charge you more because of your health. Once it closes, in most states you can be asked health questions, charged more, or turned down. This is the deadline people regret missing, because unlike the others it does not come round again each year.

Drug coverage runs on a 63-day rule

Part D timing is separate from everything above. Go 63 days or more after your Initial Enrollment Period without a Part D plan or other creditable drug coverage and a penalty is added to your premium for as long as you have drug coverage. Unless you genuinely have coverage that counts, join a drug plan when you first enroll, even if you take no medication today.

What it costs, and where to get unbiased help

Costs to Keep in Mind whichever window you use: your Part B premium is due regardless, $202.90 as the 2026 standard amount, with higher earners paying more, and signing up late raises it permanently. If you want advice with nothing attached to it, every state runs a State Health Insurance Assistance Program offering free unbiased counseling on your healthcare coverage choices, and a licensed insurance agent can compare plans with you at no cost.

Common questions

More in Medicare 101

• Turning 65: Your complete guide to starting Medicare
• Medicare Eligibility: Who Qualifies, and When
• How to Enroll in Medicare, Step by Step
• Medicare and Working Past 65: When to Enroll and What to Keep
• The Parts of Medicare, Explained: A, B, C and D
• Medicare Late Enrollment Penalties, and How to Avoid Them
• Medicare Costs: What You'll Actually Pay
• Medicare Advantage vs. Medicare Supplement: How to Choose
• Medicare Prescription Drug Coverage: Where It Comes From and How It Works