Medicare Enrollment Periods Explained: When to Sign Up

Medicare has several sign-up windows, and each one does a different job. Your first and most important chance is the Initial Enrollment Period around your 65th birthday. After that, there is a once-a-year window for Part A and Part B if you missed your first chance, a fall window for changing health and drug plans, and Special Enrollment Periods for life changes such as retiring from a job that provided health insurance. Knowing which window applies to you can protect you from gaps in coverage and from late penalties that can last as long as you have Medicare.

Your Initial Enrollment Period: The Big One

For most people, the first opportunity to sign up comes when they turn 65. According to Medicare's page on when Medicare coverage starts, this Initial Enrollment Period lasts for 7 months, starting 3 months before you turn 65, and ending 3 months after the month you turn 65.

That seven-month stretch matters for two reasons. First, the month you sign up decides when your coverage begins. Coverage always starts on the first of the month. If you sign up for Part B in the months before your birthday month, coverage can begin the month you turn 65. If you wait until your birthday month or the months after it, coverage starts the following month. Signing up early in the window is the simplest way to avoid a gap.

Second, missing the window entirely can cost you. If you skip Part B during your Initial Enrollment Period and do not have qualifying coverage from a current job, you may have to wait for a later window and pay a monthly penalty.

Do you have to sign up, or is it automatic?

Some people are enrolled automatically. Medicare's guide on how to sign up explains that if you already get Social Security or Railroad Retirement Board benefits when you reach 65, you will generally get Part A and Part B without applying, and a welcome package with your Medicare card arrives in the mail before coverage begins.

If you are not yet collecting Social Security, you need to sign up yourself. The easiest route is online through your my Social Security account, or you can contact Social Security directly. This is common now that many people delay retirement benefits to get a larger check, a decision we explain in our guide on how to decide when to claim Social Security. Delaying Social Security does not delay the need to think about Medicare at 65.

The General Enrollment Period: A Second Chance With Strings Attached

If you missed your Initial Enrollment Period and do not qualify for a Special Enrollment Period, Medicare gives you a yearly fallback. You can sign up between January 1 and March 31 each year. Coverage starts the month after you sign up.

The catch is the late enrollment penalty. Medicare's page on avoiding late enrollment penalties says the Part B penalty is an extra 10% for each full 12-month period you could have signed up but did not. It is added to your monthly premium, it is not a one-time fee, and for most people it lasts as long as they have Part B.

Medicare gives a concrete example: someone who waited two full years without qualifying for a Special Enrollment Period would pay a 20% late enrollment penalty on top of the standard Part B monthly premium, which Medicare lists as $202.90 in 2026. Because that penalty is tied to the premium, it can grow over the years as premiums change.

Most people get Part A without a premium. If you are one of the people who must buy Part A and you do not do so when first eligible, Medicare says your monthly Part A premium may go up 10%, and you pay that higher amount for twice the number of years you went without signing up.

Special Enrollment Periods: When You Are Still Working

Many Americans keep working past 65, or are covered by a working spouse's employer plan. In that case, you may be able to delay Part B without a penalty and sign up later during a Special Enrollment Period.

Medicare explains that this Special Enrollment Period starts after your Initial Enrollment Period ends and lasts up to 8 months after the group health plan coverage or the employment ends, whichever happens first. Two details trip people up:

• COBRA does not count. Medicare states that COBRA isn't considered group health plan coverage. Having COBRA after you leave a job does not extend your eight-month window.
• Retiree coverage does not count either. Losing retiree coverage or COBRA is listed by Medicare among the situations that do not qualify for a Special Enrollment Period.

There are other Special Enrollment Periods for specific situations, such as losing Medicaid, being affected by a declared disaster or emergency, or getting incorrect information from an employer or health plan. Many of them use form CMS-10797, sent to your local Social Security office. If your situation is unusual, call Social Security before a deadline passes.

A word on drug coverage

Part D has its own penalty. Medicare says you pay an extra 1% for each month (12% a year) if you do not join a drug plan when you first get Medicare and you go 63 days or more without creditable drug coverage. "Creditable" means coverage that is at least as good as standard Medicare drug coverage, such as many employer plans. Your employer or plan should tell you each year whether your drug coverage is creditable, so keep that notice.

Open Enrollment: The Fall Window for Changing Plans

Once you have Medicare, the yearly Open Enrollment Period is your regular chance to review and change your plans. According to Medicare's page on joining a health or drug plan, the Open Enrollment Period runs October 15 to December 7. During this time you can:

• Switch from Original Medicare to a Medicare Advantage Plan, or from Medicare Advantage back to Original Medicare.
• Join, drop or switch Medicare Advantage Plans, with or without drug coverage.
• Join, drop or switch a stand-alone Medicare drug plan if you are in Original Medicare.

Changes you make take effect January 1 of the next year, and the plan must get your request by December 7.

There is also a Medicare Advantage Open Enrollment Period from January 1 to March 31, but only for people already enrolled in a Medicare Advantage Plan. During that window you can switch to a different Medicare Advantage Plan or drop it and return to Original Medicare, and you can also join a separate drug plan.

Plans change their premiums, covered drugs and provider networks from year to year, so it is worth reviewing your plan every fall even if you are happy with it. Saving money on prescriptions is one of the most common reasons people switch.

Next Steps: A Simple Medicare Enrollment Checklist

1. Mark your Initial Enrollment Period. Count back three months from your 65th birthday month and forward three months after it. Aim to sign up early in that window.
2. Check whether you will be enrolled automatically. If you are not getting Social Security benefits yet, plan to sign up through Social Security yourself.
3. If you are still working, ask your employer's benefits office whether your coverage is from current employment and whether your drug coverage is creditable. Keep written proof.
4. Write down your deadlines. Note the eight-month window after job-based coverage ends, and remember that COBRA does not extend it.
5. Review plans every fall. Put October 15 on your calendar and compare plans using the Medicare Plan Finder.
6. Get free, unbiased help. Your State Health Insurance Assistance Program (SHIP) offers one-on-one Medicare counseling, and SHIPs are not connected to any insurance company. You can also call 1-800-MEDICARE (1-800-633-4227); TTY users can call 1-877-486-2048.

Medicare decisions are easier when you get ahead of the calendar. A few phone calls in the months before you turn 65 can save you years of avoidable penalties, and the same planning mindset helps with everyday costs too, such as the senior discounts worth asking for.