Medicare Enrollment Periods: IEP, GEP, SEP, AEP

Initial Enrollment Period: your seven months

Your Initial Enrollment Period runs for seven months: the three months before the month you turn 65, your birthday month, and the three months after. If you sign up in the three months before you turn 65, coverage can start the first day of your birthday month. If your birthday falls on the first of the month, the window shifts one month earlier. If you already receive Social Security benefits, Medicare enrolls you automatically in Parts A and B. Everyone else must sign up. This is the only window with no penalty for signing up on time.

General Enrollment Period: January 1 to March 31

General Enrollment runs January 1 through March 31 each year, for people who missed their Initial Enrollment Period and do not qualify for a Special Enrollment Period. Coverage starts the month after you sign up. That start date changed in 2023. Before then, coverage waited until July 1. Late enrollment penalties can still apply, and the months you went without coverage are months you pay for yourself.

Annual Enrollment Period: October 15 to December 7

Annual Enrollment, also called Open Enrollment, runs October 15 through December 7 each year. It is the window to join, switch, or drop a Medicare Advantage plan or a Part D drug plan, for coverage starting January 1. It is not the window to join Part B for the first time. That is what the Initial and General Enrollment Periods are for. If your plan still fits, you do not have to do anything, but read the Annual Notice of Change first, because premiums, drug lists, and networks change every year.

Medicare Advantage Open Enrollment: January 1 to March 31

If you are already in a Medicare Advantage plan, the Medicare Advantage Open Enrollment Period runs January 1 through March 31. It gives you one change: switch to another Advantage plan, or return to Original Medicare and add a Part D drug plan. Coverage starts the first day of the month after the plan receives your request. You cannot use this window to join an Advantage plan from Original Medicare.

Special Enrollment Periods: life changes

A Special Enrollment Period opens when life changes. A move to a new service area, losing employer coverage, a plan leaving your county, and gaining or losing Medicaid can each open one. The length varies by event. Most last two months after the event. The workhorse is the employer rule: if you had group health coverage through current employment with 20 or more employees, you get eight months to join Part B after that employment or coverage ends, with no late penalty. COBRA and Marketplace plans do not count as employer coverage for this rule, so they do not delay the penalty.

The penalties for waiting

The Part B penalty adds 10 percent to your monthly premium for each full 12-month period you went without Part B or employer group coverage, and it generally lasts as long as you have Part B. The Part D penalty adds 1 percent of the national base beneficiary premium for each month you went without creditable drug coverage, and it also generally lasts as long as you have Part D. For 2027 the base beneficiary premium is $41.33 a month, so a year without drug coverage adds about $5 a month to your premium. Penalties are the reason the first window matters most.

Your records checklist

1. Mark your 65th birthday month and count three months back.
2. Confirm whether your employer coverage counts for a delay.
3. Keep proof of employer coverage from the day it ends.
4. Read the Annual Notice of Change every September.
5. Ask about a Special Enrollment Period before you assume you must wait.

Common questions

When should I sign up for Medicare?

In the three months before the month you turn 65, so coverage can start the first day of your birthday month. If you already receive Social Security, Medicare enrolls you automatically. If you have employer coverage from a job with 20 or more employees, you can delay Part B without penalty.

What happens if I miss my Initial Enrollment Period?

You generally wait for General Enrollment, January 1 through March 31, and coverage starts the month after you sign up. A late enrollment penalty can apply to Part B and Part D, unless you had employer group coverage or another qualifying event.

Can I change plans outside Annual Enrollment?

Only with a qualifying event that opens a Special Enrollment Period, such as a move or losing employer coverage, or during the Medicare Advantage Open Enrollment Period, January 1 through March 31, if you are already in an Advantage plan.

Does COBRA delay the Part B penalty?

No. COBRA and Marketplace plans do not count as employer group coverage for Medicare's delay rules. If you are 65 or older and relying on COBRA, enroll in Part B on time or the penalty can apply.

How long does the Part B penalty last?

Generally as long as you have Part B. It adds 10 percent to your premium for each full 12-month period you went without Part B or employer group coverage.

Sources and current instructions

Check the tax year and any later updates before acting. These are the primary sources used for this guide.

• Medicare: When you can join, switch, or drop a plan
• Medicare: Special Enrollment Periods
• SSA: Medicare premiums