The calendar

The Medicare calendar: six windows, six sets of permissions

Two windows return every year, two happen once in a lifetime, and two open because of a life event. Each one permits something slightly different. Mixing them up is the most common reason people stay in a plan they have outgrown.

Figures reviewed for 2026

Oct 15 – Dec 7
Fall open enrollment: Jan 1 – Mar 31
Spring window for Advantage members: 8 months
After employer coverage ends: 6 months
One-time supplement protection

The short version

Read the table first. The detail follows below it, in the order most people encounter each window.

Which window allows which change

Window	Timing	Open to	What it permits
Initial Enrollment	Seven months around the 65th birthday	People new to Medicare	Filing for Parts A, B and D
Fall open enrollment	October 15 to December 7	Anyone with Medicare	Join, switch or drop Advantage and drug plans, effective January 1
Advantage window	January 1 to March 31	Current Advantage members	One change: another Advantage plan, or back to government Medicare
General Enrollment	January 1 to March 31	People who missed the first window	Filing for Parts A and B, possibly with surcharges
Special Enrollment	Eight months after a qualifying event	People losing group coverage or relocating	Filing or changing plans off-calendar
Supplement open enrollment	Six months from the Part B start	Enrollees 65 and older	Any Medigap policy, no health questions

The fall window, October 15 to December 7

This is the season of mailboxes full of brochures, and the window most people mean by open enrollment. Inside it you can move from government Medicare into an Advantage plan, go from one Advantage plan to another, leave Advantage behind, or replace a stand-alone drug plan. Whatever you do takes effect January 1.

What it will not do is hand you a supplement. Someone leaving Advantage in December for government Medicare may still face health questions when applying for Medigap in January. That sequencing gap catches people every single year, so line up the supplement before you cancel anything.

The spring window, January 1 to March 31

Already inside an Advantage plan? You get one change in the first quarter. Move to a different Advantage plan, or leave Advantage for government Medicare and add a stand-alone drug plan in the same action.

You cannot use it to swap stand-alone drug plans while on government Medicare, and it is a single change rather than a series of experiments. File in February and the switch generally starts March 1.

Special windows opened by life events

Certain events reset the calendar. Losing employer coverage gives eight months from the month employment or the coverage ends. Relocating outside a plan’s service area, losing Medicaid eligibility, entering or leaving a care facility, and a handful of similar situations each create their own shorter window, usually two months.

Move quickly and keep the paper. These windows are usually tied to a date printed on a document, and both the plan and Social Security will ask to see it.

The January to March rescue for first-timers

Missed the original window and no life event applies? General Enrollment, January 1 through March 31, is the yearly chance to file for Parts A and B. Benefits typically begin the first of the following month, and surcharges usually attach for as long as Part B stays active.

What a missed window quietly adds

Part B adds 10 percent for every full twelve months of eligible-but-unenrolled time, permanently. Part D adds 1 percent of the national base beneficiary premium for each month without creditable drug coverage, also permanently. Neither is a one-time fee, and neither disappears when you change plans.

Official source

The federal guide behind this page

Medicare publishes its own handbook on this topic. It is linked here so you can check any figure on this page against the source.

Your Medicare in 2027: What’s New & ChangingCMS 12229Read the PDF
Remember Key Medicare DatesCMS 12192Read the PDF
Understanding Medicare Advantage & Drug Plan Enrollment PeriodsCMS 11219Read the PDF Order print

Every official Medicare publication, in one library

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The calendar

Questions people ask about this

Can I make a change outside these dates?

Only when a special enrollment period applies, such as a move, the loss of group coverage, or a shift in Medicaid eligibility. Otherwise the next window is your opening.

How do I leave an Advantage plan for government Medicare?

Use fall open enrollment or the January to March Advantage window. Plan the supplement first: once past your one-time protection, buying Medigap may involve health questions unless your state adds rights.

Does fall open enrollment cover Medigap?

No. Medigap sits outside the enrollment calendar entirely. You may apply for a different policy in any month, but outside your initial window the insurer can review your health.

I enrolled in November. When does it start?

January 1 for anything done in fall open enrollment. Changes made in the Advantage window start the first of the month after the plan receives your request.

Official sources

Check it at the source

Every figure on this page comes from the agencies below. They are the primary record, and none of these links costs you anything.

Keep reading

Turning 65 timelineYour first window, step by step Late enrollment penaltiesHow the surcharges are calculated Compare Supplement to AdvantageWhich path suits your year Working past 65The eight-month special window

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