Medicare enrollment happens during specific windows, and missing yours can cost you in penalties

You can enroll in Medicare during your Initial Enrollment Period, which runs for seven months starting three months before the month you turn 65. If you miss that window, you can still enroll during the General Enrollment Period (January 1 to March 31 each year), but you will pay a permanent penalty on your premiums for each year you delayed. The fastest way to enroll is online at Medicare.gov, by phone at 1-800-MEDICARE, or in person at your local Social Security office.

The process itself is straightforward: you provide your name, date of birth, and Social Security number. Medicare will check your records to see if you already have coverage through an employer or union. If you do, you may not need to enroll right away — but you should verify this before your coverage ends, because the rules differ depending on your situation.

Key Takeaways

  • Your Initial Enrollment Period is seven months long, starting three months before the month you turn 65, and this is when you should enroll to avoid penalties.
  • You can enroll online at Medicare.gov, by phone at 1-800-MEDICARE, or at your local Social Security office — all three routes take about the same time.
  • If you have health coverage through a current job or union, you may be able to delay enrollment without penalty, but you must tell Medicare about that coverage when you do enroll.
  • Part A (hospital insurance) is usually free if you or your spouse paid Medicare taxes for at least 10 years, but Part B (medical insurance) has a monthly premium that increases if you delay.
  • You will need your Social Security number and information about any current health coverage, but you do not need to visit an office — online enrollment takes about 10 minutes.

Understanding your enrollment window and why it matters

Your Initial Enrollment Period 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 — that is seven months total. During this time, you can enroll in Medicare Part A and Part B without any waiting period or penalty.

If you do not enroll during your Initial Enrollment Period, you enter the General Enrollment Period, which runs January 1 to March 31 each year. You can enroll then, but your Part B coverage will not start until July 1 of that year, leaving you uninsured for several months. You will also pay a 10 percent penalty on your Part B premium for each full year you delayed — and that penalty stays with you for life.

There is one major exception: if you have health coverage through a current job (yours or your spouse's), you can delay Part B enrollment without penalty. This is called creditable coverage. When you finally leave that job or lose that coverage, you have eight months to enroll in Part B without penalty. You must tell Medicare about your employer coverage when you enroll, so keep your insurance documents handy.

How to enroll online, by phone, or in person

The online route is the fastest. Go to Medicare.gov, click "Enroll in Medicare," and follow the prompts. You will need your Social Security number, date of birth, and information about any current health coverage. The form takes about 10 minutes. You will receive a confirmation number on screen and by email.

If you prefer to call, dial 1-800-MEDICARE (1-800-633-4227). A representative will walk you through the same questions and enroll you over the phone. The call usually takes 15 to 20 minutes. Have your Social Security card and any insurance documents nearby.

You can also visit your local Social Security office in person. Bring your Social Security card, proof of citizenship (passport, birth certificate, or naturalization papers), and proof of residence (utility bill or lease). The office will enroll you on the spot. Wait times vary by location, so call ahead to ask about busy hours.

What documents and information you will need

At minimum, you need your Social Security number and date of birth. If you are enrolling online or by phone, that is often all Medicare will ask for — they can look up the rest in their system.

If you have current health coverage through an employer, a union, or a spouse's job, have that information ready. You will need the name of the plan and the date your coverage started. This tells Medicare whether you can delay Part B without penalty. If you are unsure whether your coverage counts as creditable, call your plan's customer service number — they can tell you in one call.

If you are enrolling in person at Social Security, bring proof of citizenship (passport, birth certificate, or naturalization papers) and proof of residence (a recent utility bill, lease, or bank statement). These are not required for online or phone enrollment, but Social Security offices ask for them to verify your identity.

Part A versus Part B: what each covers and what it costs

Part A covers hospital stays, skilled nursing facility care, hospice, and some home health services. Most people do not pay a monthly premium for Part A if they or their spouse paid Medicare taxes for at least 10 years. If you did not, you can still enroll, but you will pay a monthly premium — the amount depends on how many years you or your spouse paid in.

Part B covers doctor visits, outpatient care, medical equipment, and preventive services. Part B has a monthly premium that most people pay. In 2024, the standard premium is $164.90 per month, but the amount changes each year and varies based on your income. If you delay enrolling in Part B beyond your Initial Enrollment Period, your premium increases by 10 percent for each full year you waited — and that increase is permanent.

When you enroll, Medicare will ask whether you want Part A, Part B, or both. Most people enroll in both. If you have coverage through a current job, you can enroll in Part A only and delay Part B until you leave that job.

What happens after you enroll

Once you enroll, Medicare will send you a Medicare card in the mail within two to four weeks. Your coverage starts on the first day of the month you turn 65, or the first day of the month after you enroll, whichever is later. For example, if you enroll in April and turn 65 in June, your coverage starts June 1. If you enroll in July after already turning 65 in June, your coverage starts August 1.

You will also receive information about Part D (prescription drug coverage) and Medigap (supplemental insurance). Part D is optional but recommended if you take any medications — enrolling during your Initial Enrollment Period avoids a penalty. Medigap helps cover costs that Medicare does not, such as copayments and deductibles. You can enroll in Medigap anytime, but the best rates are usually available during your first six months in Medicare Part B.

Keep your Medicare card with you at all times. Show it to your doctor, hospital, or pharmacy when you receive care. If you lose your card, you can request a replacement at Medicare.gov or by calling 1-800-MEDICARE.

Special situations: working past 65, coverage through a spouse, or delayed enrollment

If you are still working at 65 and have health coverage through your job, you do not have to enroll in Medicare right away. You can delay Part B enrollment without penalty as long as your employer has 20 or more employees and you are actively working. When you leave that job or lose that coverage, you have eight months to enroll in Part B without penalty. You should still enroll in Part A, since it is usually free and has no penalty for delay.

If you are covered under your spouse's employer plan, the same rule applies — you can delay Part B without penalty. When your spouse retires or loses coverage, you have eight months to enroll. Again, enroll in Part A right away.

If you missed your Initial Enrollment Period and did not have creditable coverage, you can still enroll during the General Enrollment Period (January 1 to March 31). Your coverage will start July 1, and you will pay a permanent 10 percent penalty on your Part B premium. If you are facing financial hardship, call 1-800-MEDICARE to ask whether you may have access to for a penalty waiver — these are rare but possible in certain situations.

Frequently Asked Questions

What if I turn 65 but do not plan to retire yet?

You can delay Part B enrollment if you have health coverage through your current job and your employer has 20 or more employees. You must still enroll in Part A. When you leave your job, you have eight months to enroll in Part B without penalty. Tell Medicare about your employer coverage when you do enroll.

Can I change my mind after I enroll?

Yes. You have until March 31 of the year after you enroll to make changes to your Part A and Part B coverage. For Part D and Medigap, you have different windows — usually 12 months from when you first enroll in Medicare. Call 1-800-MEDICARE to discuss your options.

Do I have to enroll in Part D when I enroll in Medicare?

Part D is optional, but if you do not enroll when you first become may be able to access and you take medications, you will pay a penalty when you do enroll. The penalty is 1 percent of the national average Part D premium for each month you were without coverage. If you do not take medications, you can skip Part D and enroll later without penalty.

What if I am not a U.S. citizen?

You must be a U.S. citizen or a permanent resident (green card holder) to enroll in Medicare. If you are a permanent resident, you must have lived in the United States for at least five consecutive years. Bring proof of your status when you enroll in person, or have it ready if you call.

How do I know if my current coverage is creditable?

Call your health plan's customer service number and ask whether your coverage is creditable for Medicare purposes. They can answer in one call. You can also ask your employer's human resources department. When you enroll in Medicare, you will report this information to Medicare — keep your plan documents for your records.