Medicare has specific times of year when you can sign up for coverage or make changes. Missing a window can mean waiting months for coverage or, in some cases, paying a late enrollment penalty. Here is a practical guide to the main enrollment periods and what each one allows.

Initial Enrollment Period (IEP)

Your Initial Enrollment Period is your first chance to sign up for Medicare. For most people it is a seven-month window around their 65th birthday: the three months before your birthday month, the month itself, and the three months after.

Signing up during the first three months generally allows coverage to begin the month you turn 65. Enrolling later in the window may push your start date back. During this period you can enroll in Part A and Part B and, once you have both, choose a Medicare Advantage plan or a stand-alone Part D plan.

Medigap Open Enrollment Period

If you are interested in a Medicare Supplement (Medigap) policy, pay attention to your Medigap Open Enrollment Period. It is a six-month window that begins the first month you are 65 or older and enrolled in Part B. During this time, insurers in most cases cannot deny you a policy or charge more because of your health history. After it ends, you may be subject to medical underwriting in many states, although some states have additional protections.

Annual Enrollment Period (AEP)

The Annual Enrollment Period, sometimes called Open Enrollment, runs from October 15 to December 7 each year. Changes take effect January 1. During AEP you can:

  • Switch from Original Medicare to a Medicare Advantage plan, or the reverse
  • Change from one Medicare Advantage plan to another
  • Join, drop or switch a Part D prescription drug plan

Plans send an Annual Notice of Change each fall describing how premiums, benefits, networks and drug lists will change. Reviewing it is one of the most useful things you can do every year, even if you were happy with your plan.

Medicare Advantage Open Enrollment Period

From January 1 to March 31, people already enrolled in a Medicare Advantage plan can make one change. You can switch to a different Medicare Advantage plan or return to Original Medicare and join a stand-alone Part D plan. This period does not allow someone with Original Medicare to move into Medicare Advantage.

General Enrollment Period

If you did not sign up for Part B (or premium Part A) when you were first eligible and do not qualify for a Special Enrollment Period, you can enroll during the General Enrollment Period from January 1 to March 31. Coverage generally starts the month after you sign up. A late enrollment penalty may apply and can last as long as you have Part B.

Special Enrollment Periods (SEPs)

Certain life events can open a Special Enrollment Period outside the usual windows. Common examples include:

  • Losing employer or union group coverage
  • Moving outside your plan's service area
  • Moving into or out of a nursing home or similar facility
  • Qualifying for Extra Help or Medicaid
  • Your plan leaving Medicare or your area

Each SEP has its own timeframe and rules, so confirm the details as soon as a change happens.

Tips for Staying on Track

Mark your calendar

Note your 65th birthday window, your Medigap open enrollment dates and the fall AEP each year.

Keep records of other coverage

If you delay Part B or Part D because you have employer coverage, keep documentation. You may need proof of creditable coverage later to avoid penalties.

Review every year

Your health, medications and plan options change. A yearly review helps make sure your coverage still fits.

Enrollment rules can be detailed and are updated from time to time. For official information, visit Medicare.gov or contact your State Health Insurance Assistance Program. A licensed agent can also help you understand which options are available where you live.