When and How to Enroll in Medicare Part B

You enroll in Medicare Part B by contacting Social Security, Medicare, or your insurance agent during your Initial Enrollment Period — the seven-calendar-month window that starts three months before the month you turn 65. You can enroll online at Medicare.gov, by phone at 1-800-MEDICARE, by visiting a Social Security office in person, or through a licensed insurance agent. Most people enroll automatically if they are already receiving Social Security benefits, but you must take action yourself if you are not yet collecting Social Security when you turn 65.

Part B covers doctor visits, outpatient care, medical equipment, and preventive services. It is not automatic — you choose to enroll and pay a monthly premium, which varies based on your income. If you miss your Initial Enrollment Period and do not have a may have access to reason, you will pay a permanent penalty on top of your regular premium for as long as you have Part B.

Key Takeaways

  • Your Initial Enrollment Period runs for seven months: three months before the month you turn 65, the month you turn 65, and three months after.
  • If you are receiving Social Security benefits when you turn 65, you are enrolled in Part B automatically unless you actively decline it.
  • If you are not yet collecting Social Security, you must contact Medicare or Social Security yourself to enroll during your Initial Enrollment Period.
  • Late enrollment penalties add a permanent surcharge to your Part B premium if you miss your Initial Enrollment Period without a may have access to reason.
  • You can enroll online at Medicare.gov, by phone, in person at a Social Security office, or through a licensed insurance agent.

Who Enrolls Automatically and Who Must Act

If you are already collecting Social Security retirement, spousal, survivor, or disability benefits when you turn 65, Medicare will enroll you in Part A and Part B automatically. You will receive a Medicare card in the mail about two weeks before your 65th birthday. You do not need to do anything unless you want to decline Part B, which you can do by returning a form that comes with your card.

If you are not yet receiving Social Security when you turn 65, you must contact Social Security or Medicare yourself. Social Security will not automatically enroll you in Part B just because you are old enough. This is the most common reason people miss their enrollment window and face penalties later. Contact Social Security at 1-800-772-1213 or visit your local Social Security office to enroll.

Your Initial Enrollment Period: The Seven-Month Window

Your Initial Enrollment Period is exactly seven calendar months long. It begins three months before the month you turn 65, includes 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. You can enroll at any point during this window — there is no advantage to enrolling early, and you will not pay premiums until the month your coverage begins.

Coverage typically starts the first day of the month you turn 65 if you enroll during your Initial Enrollment Period. If you enroll after your birthday month, your coverage may start the first day of the following month. The exact start date depends on when you enroll and which month you turn 65, so confirm the date with Medicare when you enroll.

What Happens If You Miss Your Initial Enrollment Period

If you do not enroll during your Initial Enrollment Period and do not have a may have access to reason, you will face a late enrollment penalty. This penalty is a permanent percentage increase added to your Part B premium for as long as you have coverage. The penalty is 10 percent of the standard Part B premium for each full 12-month period you were may be able to access but not enrolled. If you were may be able to access for three years and did not enroll, your penalty would be 30 percent of the standard premium, and you would pay it every month for life.

may have access to reasons that waive the penalty include being covered by an employer health plan while you or your spouse was still working, or having end-stage renal disease. If you believe you have a may have access to reason, bring documentation when you enroll. Medicare will review your case, but the burden is on you to prove the reason was valid.

How to Enroll: Four Routes

Online at Medicare.gov: Visit Medicare.gov, select "Enroll in Medicare," and follow the steps. You will need your Social Security number and birth date. This is the fastest route if you are comfortable with online forms.

By phone: Call 1-800-MEDICARE (1-800-633-4227). Representatives are available seven days a week. Have your Social Security number and birth date ready. Wait times are often shorter early in the morning or on weekdays.

In person at a Social Security office: Visit your local Social Security office with your Social Security card and proof of citizenship or legal residency. No appointment is needed, but you may wait. Find your nearest office at ssa.gov.

Through a licensed insurance agent: An agent who sells Medicare plans can help you enroll in Part B at the same time you choose a supplemental or Medicare Advantage plan. Agents do not charge you — they are paid by the insurance company — but confirm they are licensed before you meet with them.

Documents and Information You Will Need

Have these items ready before you contact Medicare or Social Security:

  • Your Social Security number
  • Your date of birth
  • Your citizenship or legal residency status (proof may be required in person)
  • Information about any current health coverage (employer plan, TRICARE, Veterans benefits)
  • Your income information if you want to know whether you may have access to for a premium subsidy

If you are enrolling in person, bring your Social Security card and a government-issued photo ID. If you are enrolling online or by phone, you will not need to submit documents at that moment, but Medicare may ask for them later to verify your information.

Income-Related Premiums and Costs

Your Part B premium depends on your income from two years ago. If your income was below a certain threshold, you pay the standard monthly premium. If your income was above that threshold, you pay a higher premium called an Income-Related Monthly Adjustment Amount (IRMAA). The thresholds and premium amounts change each year.

When you enroll, Medicare will use your most recent tax return to calculate your premium. If your income has dropped significantly since then — because you retired, lost a job, or had a major life change — you can request a reduction. Contact Medicare at 1-800-MEDICARE to ask about a reduction based on a life-changing event.

What Happens After You Enroll

After you enroll, Medicare will send you a card by mail within two weeks. Your card shows your Medicare number, which you will use for all medical appointments and claims. Your Part B coverage will start on the first day of the month you turn 65 (or the first day of the following month if you enroll after your birthday month).

Your first premium payment will be deducted from your Social Security check if you are receiving benefits, or you will receive a bill by mail if you are not. Part B premiums are deducted automatically each month going forward. If you want to change how you pay — for example, to pay by bank account instead of Social Security deduction — contact Medicare to update your payment method.

Frequently Asked Questions

Do I have to enroll in Part B when I turn 65?

No. Part B is optional, and you can decline it. However, if you decline and later want to enroll outside your Initial Enrollment Period, you will face a permanent late enrollment penalty unless you have a may have access to reason. Most people enroll because the penalty makes it expensive to wait.

What if I am still working and have health coverage through my employer?

You can delay enrolling in Part B without penalty if you or your spouse is still working and you have group health coverage through that job. When you or your spouse stops working, you have eight months to enroll in Part B without penalty. Contact Medicare to confirm your employer coverage qualifies before you decide to delay.

Can I enroll in Part B after I turn 65?

Yes, as long as you enroll within your seven-month Initial Enrollment Period. If you turn 65 in June, you can enroll anytime from March through September. After September, you can still enroll, but you will face a late enrollment penalty unless you have a may have access to reason.

Will my Part B premium change after I enroll?

Yes. Your premium is recalculated each year based on your income from two years prior. If your income increases, your premium may increase. If your income drops, you can request a reduction by contacting Medicare and providing proof of the change.

What if I enrolled automatically but I do not want Part B?

You can decline Part B by returning the form that comes with your Medicare card, or by contacting Social Security. You must decline within your Initial Enrollment Period to avoid being charged premiums. If you decline and later want to enroll, you will face a late enrollment penalty unless you have a may have access to reason.