Medicare has three main enrollment windows each year, and missing them can cost you money

The Initial Enrollment Period is a seven-month window that starts three months before the month you turn 65 and ends three months after. If you sign up during this window, your coverage can start as early as the first day of your birth month. If you wait until after this period ends, you will face a permanent penalty on your premiums — typically 10 percent for Part B and 1 percent per month for Part D — for as long as you have Medicare.

The General Enrollment Period runs from January 1 to March 31 each year. You can sign up for Part A or Part B during this time if you missed your Initial Enrollment Period, but coverage does not start until July 1 of that year. The penalty still applies if you enroll late.

The Annual Enrollment Period, also called Open Enrollment, runs from October 15 to December 7 each year. This is when you can switch between Medicare Advantage and Original Medicare, change your prescription drug plan, or join a Medigap policy. Changes take effect January 1 of the following year. You do not face a penalty for switching plans during this window.

Key Takeaways

  • Your Initial Enrollment Period is a seven-month window centered on your 65th birthday — three months before and three months after the month you turn 65.
  • If you enroll during your Initial Enrollment Period, coverage can start as early as the first day of your birth month with no penalty.
  • Missing your Initial Enrollment Period triggers a permanent 10 percent penalty on Part B premiums and 1 percent per month on Part D premiums for life.
  • The Annual Enrollment Period from October 15 to December 7 lets you change plans each year without penalty, but you cannot sign up for the first time during this window.
  • If you have employer health insurance and delay Medicare, you may have a Special Enrollment Period that protects you from the late penalty.

The Initial Enrollment Period: Your first chance to sign up

Your Initial Enrollment Period is the most important important date. It begins three months before the month you turn 65 and ends three months after. For example, if you turn 65 in June, your window opens in March and closes in September.

During this seven-month period, you can sign up for Part A (hospital insurance), Part B (medical insurance), and Part D (prescription drug coverage). If you enroll in the first three months of your window — before your birth month — your coverage starts on the first day of your birth month. If you enroll during your birth month or the three months after, coverage starts on the first day of the following month.

The penalty for missing this important date is steep and permanent. If you do not sign up for Part B when you are first may be able to access, you will pay a 10 percent higher premium for Part B for as long as you have Medicare. If you do not sign up for Part D, you will pay 1 percent of the national average premium for each month you were without coverage — a penalty that compounds over time. These penalties do not go away if you sign up later.

Special Enrollment Periods: When you get a second chance

If you have health insurance through your employer or your spouse's employer when you turn 65, you may may have access to for a Special Enrollment Period. This gives you up to eight months after your employment ends or your coverage ends — whichever comes first — to sign up for Medicare without the late penalty.

To use this protection, you must sign up within this eight-month window. You will need to show proof that you had employer coverage, such as a letter from your employer's benefits office or a copy of your health plan documents. If you wait longer than eight months after losing employer coverage, the penalty applies.

Other life events that may trigger a Special Enrollment Period include losing Medicaid, moving out of your health plan's service area, or having your plan terminate. Contact Medicare directly at 1-800-MEDICARE to find out whether your situation qualifies.

The Annual Enrollment Period: Changing plans each year

Every year from October 15 to December 7, you can make changes to your Medicare coverage. This is when you can switch from Original Medicare to a Medicare Advantage plan, switch from Medicare Advantage back to Original Medicare, change your prescription drug plan, or enroll in a Medigap policy for the first time if you have Original Medicare.

Changes you make during this window take effect on January 1 of the following year. You do not face a penalty for switching plans during Annual Enrollment, even if you are switching for the first time. However, you cannot use this period to sign up for Medicare if you have never had it — you must use your Initial Enrollment Period or General Enrollment Period for that.

The General Enrollment Period: A backup option with a catch

If you missed your Initial Enrollment Period, the General Enrollment Period runs from January 1 to March 31 each year. You can sign up for Part A or Part B during this time, and coverage will start on July 1 of that year.

The drawback is the penalty. Because you are signing up late, you will pay a 10 percent higher premium on Part B for as long as you have Medicare. This penalty is permanent — it does not disappear after a certain number of years. If you also need to sign up for Part D, you will face the 1 percent monthly penalty as well. The General Enrollment Period is a safety net, but it is an expensive one.

How to sign up during your enrollment period

You can sign up for Medicare in three ways: online at Medicare.gov, by phone at 1-800-MEDICARE, or in person at your local Social Security office. If you are signing up online, you will need your Social Security number and information about any current health coverage you have.

If you are signing up by phone, a Medicare representative can walk you through the process and answer questions about which parts of Medicare you need. The call is free. If you prefer to sign up in person, you can visit your local Social Security office — no appointment is needed, though wait times vary by location.

Keep copies of any confirmation documents Medicare sends you. These show your coverage start date and which parts of Medicare you enrolled in. You will need this information when you contact your health insurance company or pharmacy.

What happens if you miss your enrollment period

If you miss your Initial Enrollment Period and do not have a Special Enrollment Period, you can still sign up during the General Enrollment Period from January 1 to March 31, but coverage will not start until July 1 and you will pay the late penalty.

If you miss the General Enrollment Period as well, you will have to wait until the next Annual Enrollment Period in October to make changes. In the meantime, you will be without Medicare coverage unless you have other insurance. The longer you go without signing up, the higher your penalties will be.

The one exception is if you have a may have access to life event — such as losing employer coverage, moving, or losing Medicaid — that triggers a Special Enrollment Period. In that case, contact Medicare right away to find out your important date and what documents you need to provide.

Frequently Asked Questions

What if I turn 65 while still working and have employer health insurance?

You can delay signing up for Medicare without penalty as long as you have employer coverage through your job or your spouse's job. When your employment ends or your coverage ends, you will have eight months to sign up for Medicare without facing the late penalty. Contact your employer's benefits office to confirm your coverage details, then sign up within that eight-month window.

Can I sign up for Medicare before I turn 65?

Your Initial Enrollment Period starts three months before your birth month, so yes — you can sign up as early as three months before you turn 65. If you sign up during those first three months, your coverage can start on the first day of your birth month. Signing up early gives you the most flexibility for your coverage start date.

What is the penalty for signing up late for Part D?

The Part D penalty is 1 percent of the national average premium for each month you were without coverage. This penalty is added to your monthly premium and stays with you for as long as you have Part D. For example, if you go without Part D for 12 months, you will pay 12 percent more than the standard premium. The penalty compounds if you go longer without coverage.

Can I change my Medicare plan outside of Annual Enrollment?

In most cases, no — you can only change plans during the Annual Enrollment Period from October 15 to December 7. However, if you have a may have access to life event such as losing coverage, moving, or getting married, you may have a Special Enrollment Period that allows you to make changes outside the annual window. Contact Medicare to learn about your situation qualifies.

What if I do not know when my Initial Enrollment Period is?

Call Medicare at 1-800-MEDICARE and provide your birth date. A representative can tell you the exact dates of your Initial Enrollment Period and help you understand which parts of Medicare you need. You can also create an account on Medicare.gov to see your enrollment status and important date.