Medicare enrollment periods and deadlines

Medicare runs on windows. Miss one and you may wait months, pay a permanent penalty, or lose a right you cannot get back. Here is every enrollment period, in the order you are likely to meet them.

The six windows at a glance

Initial Enrollment Period — the seven months

Your IEP is seven months long: the three months before your 65th birthday month, your birthday month, and the three months after.

When your coverage starts depends on when inside that window you apply:

The practical implication is simple: apply in the first three months if you want coverage to start the month you turn 65. Applying later delays your start date, and it delays your Medigap window with it.

Remember the birthday rule — if you were born on the first of a month, everything shifts one month earlier. Work out your exact dates here.

Medigap Open Enrollment — the one you cannot get back

Six months, starting the month your Part B coverage begins, provided you are 65 or older.

Inside this window, a Medicare Supplement carrier:

• Must sell you any Medigap policy it offers in your state
• Cannot ask about your health history
• Cannot charge you more because of a pre-existing condition
• Cannot decline your application

Once it closes, in most states all of that reverses. The carrier can require a health questionnaire, rate you up, impose a waiting period for pre-existing conditions, or simply say no.

Some states apply more generous rules. Massachusetts, Connecticut, New York and Maine each have additional consumer protections, and several states have annual birthday or anniversary rules allowing a switch without underwriting. If you live in one of them the picture is friendlier than the national default — worth an actual conversation rather than a rule of thumb.

There are also guaranteed-issue rights outside the open enrollment window in specific circumstances: your Medicare Advantage plan leaves your service area, you move out of the plan’s area, your employer coverage ends, or you are within the twelve-month trial right after joining an Advantage plan for the first time at 65.

Annual Enrollment Period — October 15 to December 7

The one everyone has heard of, because it is the one advertised at you relentlessly every autumn.

During AEP you can:

• Join a Medicare Advantage plan
• Switch from one Advantage plan to another
• Drop an Advantage plan and return to Original Medicare
• Join, switch or drop a standalone Part D plan

All changes take effect January 1.

AEP does not give you a right to buy a Medigap policy without underwriting. That is the most consequential misunderstanding about this window — leaving Advantage during AEP is easy, and getting a supplement afterwards may not be.

This is also the window our annual coverage review is built around, because every plan changes on January 1: formularies, tiers, networks, premiums and cost sharing. The Annual Notice of Change your carrier mails each September tells you exactly what moved, and it is the most useful piece of mail you receive all year.

Medicare Advantage Open Enrollment — January 1 to March 31

A narrower window, and only for people already enrolled in a Medicare Advantage plan on January 1. You get one change:

• Switch to a different Medicare Advantage plan, or
• Return to Original Medicare and join a standalone Part D plan

It does not let someone on Original Medicare join an Advantage plan, and it does not create a Medigap guaranteed-issue right. Its practical role is a safety valve: you enrolled in January, discovered in February that your specialist is not in the network, and you have until March 31 to fix it.

General Enrollment Period — January 1 to March 31

The fallback for people who missed their Initial Enrollment Period and have no Special Enrollment Period available. Enroll during GEP and coverage now begins the first day of the month after you enroll.

The GEP is also where the Part B late-enrollment penalty shows up. The penalty is 10 percent of the standard Part B premium for each full twelve-month period you were eligible and not enrolled, added to your premium for as long as you have Part B. Twenty-four months late is a 20 percent surcharge, permanently.

There is a parallel Part D late-enrollment penalty for going 63 days or more without creditable drug coverage, calculated per uncovered month and likewise permanent.

Special Enrollment Periods — the ones people miss

SEPs are triggered by life events, and they are the least-known and most useful windows in the system. Common triggers include:

• Losing employer or union coverage — an 8-month SEP for Part B, and a shorter one for Part D and Advantage plans
• Moving to an address outside your plan’s service area, or to an area with new plan options
• Your plan leaving your county, or ending its contract with Medicare
• Entering or leaving a skilled nursing facility or long-term care institution
• Qualifying for Extra Help, Medicaid or a Medicare Savings Program
• Losing Extra Help or Medicaid eligibility
• A federally declared disaster or emergency in your area
• Enrollment errors caused by a federal employee or plan representative

Most SEPs run two months from the qualifying event, though the Part B SEP for loss of employer coverage runs eight. They generally require documentation, and they are easy to let slip: someone spends the first month of a job loss dealing with everything else and finds the window when it has nearly closed.

A calendar to keep

What to do

If you are approaching 65, start with the turning 65 checklist and run your dates through the enrollment window checker.

If you are already on Medicare, put a note in your calendar for early October. A twenty-minute annual review each autumn is the difference between choosing your plan and being auto-renewed into one.