Most of the anxiety around Medicare is really anxiety about missing something. So here is every window that matters, in one place, with the consequence of missing it stated plainly.

Your Initial Enrollment Period

Seven months, built around your 65th birthday: the three months before your birthday month, your birthday month itself, and the three months after.

Your is the one window where the most doors are open at once, including your one-time Medigap window. It is worth treating as the real deadline even when a Special Enrollment Period would technically bail you out later.

The Annual Enrollment Period

October 15 to December 7, every year, for everyone already on Medicare. Changes you make take effect January 1.

During you can switch Medicare Advantage plans, move between Original Medicare and Medicare Advantage, join or change a Part D plan, or drop drug coverage.

The Medicare Advantage Open Enrollment Period

January 1 to March 31, for people already in a Medicare Advantage plan. One change allowed: switch to a different Medicare Advantage plan, or drop back to Original Medicare and pick up a Part D plan.

Again — dropping back to Original Medicare does not automatically give you a Medigap right.

Special Enrollment Periods

A opens when a qualifying life event gives you one. The common ones:

  • Losing active employer coverage. Eight months for Part B, two months for Part D and Medicare Advantage. These clocks are different lengths and they start at different moments — this trips people constantly.
  • Moving out of your plan's service area.
  • Your plan leaving your area or ending its Medicare contract.
  • Qualifying for or for both Medicare and Medicaid.

COBRA is not active employer coverage. Neither is retiree coverage. Neither is a severance health benefit.

Worth repeating

If you are relying on any of those three to delay Part B, stop and confirm it before your birthday. They do not create a Part B Special Enrollment Period, and they do not protect you from the penalty.

The General Enrollment Period

January 1 to March 31, for anyone who missed Part B and does not qualify for a Special Enrollment Period. Coverage begins the month after you enroll.

The is the safety net, not a plan. Landing here usually means you have already started accruing the Part B penalty.

The two permanent penalties

  • Part B: 10% added to your premium for each full 12-month period you could have had it and did not. Paid every month, for as long as you have Part B.
  • Part D: 1% of the national base beneficiary premium for each month you went without creditable drug coverage, once you hit 63 days uncovered. Also permanent.
  • Both are avoidable entirely. Neither is negotiable once it starts.

The date that catches almost everyone

Not a deadline at all — a habit. Every fall, your plan sends an Annual Notice of Change describing what is different for next year: the drug list, the network, the cost sharing.

It arrives in September, it looks like junk mail, and almost nobody reads it. Then in February someone finds out their prescription moved to a tier that costs four times as much, and the window to do anything about it closed on December 7.

Find your window

Two minutes, five questions, and you will know which of these applies to you right now.