When and How to Sign Up for Part B Coverage

You enroll in Medicare Part B by submitting a form to Social Security or Medicare, either online, by mail, or in person at a Social Security office. The timing matters: you have a window called your Initial Enrollment Period that runs for seven months — it starts three months before the month you turn 65 and ends three months after. If you miss this window, you pay a permanent penalty on your Part B premium for as long as you have Medicare, unless you had other health coverage that delayed your enrollment.

Most people become may be able to access for Medicare the month they turn 65. If you are already receiving Social Security benefits, Medicare will enroll you automatically in Part A and Part B unless you decline Part B in writing. If you are not yet receiving Social Security, you must take action yourself — Social Security will not assume you want Part B.

Key Takeaways

  • Your Initial Enrollment Period is seven months long: three months before, the month of, and three months after you turn 65.
  • If Social Security is already paying you, you are enrolled in Part B automatically unless you actively decline it.
  • If you have not claimed Social Security yet, you must contact Medicare or Social Security yourself to enroll in Part B.
  • Missing your enrollment window triggers a permanent 10 percent penalty on your Part B premium for each full year you delayed.
  • You can enroll online at Medicare.gov, by phone at 1-800-MEDICARE, by mail, or at your local Social Security office.

What Documents and Information You Need

Gather your Social Security number, date of birth, and current mailing address before you start. You will also need information about any other health coverage you currently have — employer coverage, COBRA, or a retiree plan — because this affects whether you owe a late-enrollment penalty. If you have coverage through a spouse's employer, bring that information too.

If you are enrolling by mail, you will need to complete Form CMS-40B (process for Enrollment in Part B). You can read this from Medicare.gov or request it by phone. The form asks for basic identification, your coverage history, and whether you want Part B. Mail it to your local Social Security office — the address is on the form itself.

Three Ways to Enroll: Online, Phone, or In Person

Online enrollment is the fastest route if you have a Medicare.gov account. Go to Medicare.gov, sign in, and select "Enroll in Part B" from your dashboard. You will answer questions about your coverage history and confirm your enrollment. This method typically takes 10 to 15 minutes and you receive confirmation when ready.

Phone enrollment means calling 1-800-MEDICARE (1-800-633-4227). A representative will walk you through the same questions, verify your identity, and enroll you on the spot. The call usually takes 15 to 20 minutes. This route works well if you have questions or need help understanding your coverage history.

In-person enrollment at a Social Security office lets you hand over documents and speak to someone face-to-face. Find your local office at ssa.gov/locator. Bring your Social Security card, proof of citizenship or legal residency (passport, birth certificate, or naturalization papers), and proof of current address (utility bill or lease). You do not need an appointment at most offices, but wait times vary — call ahead to ask about busy times.

What Happens After You Enroll

Once you enroll, Medicare sends you a Medicare card in the mail within two to three weeks. Your Part B coverage starts on the first day of the month after you enroll, unless you enroll during your Initial Enrollment Period, in which case coverage starts the first of the month you turn 65 (or the first of the month after, depending on your birth date).

Your Part B premium is deducted from your Social Security check each month, or you receive a bill if you are not yet receiving benefits. The premium amount depends on your income from two years ago — higher earners pay more. Medicare will tell you the exact amount when you receive your card.

Late Enrollment Penalties and How to Avoid Them

If you do not enroll during your Initial Enrollment Period and you do not have a valid reason for the delay, you owe a late-enrollment penalty. The penalty is 10 percent of the standard Part B premium for each full year you were may be able to access but not enrolled. This penalty stays on your premium for as long as you have Part B — it does not go away after a few years.

You can avoid the penalty if you had creditable coverage — health insurance through an employer, a spouse's employer, COBRA, Medicaid, the VA, or the Federal Employees Health Benefits Program — during the time you were not enrolled in Part B. You must show proof of this coverage. If you had a gap of more than 63 days between when your other coverage ended and when you enrolled in Part B, the penalty applies to the gap period.

If you believe you have a valid reason for late enrollment, contact Medicare at 1-800-MEDICARE and ask about a Special Enrollment Period. These exist for people who lost employer coverage, moved out of the country, or had other may have access to events.

If You Want to Decline Part B

You can refuse Part B enrollment if you have other coverage that meets Medicare's standards. To decline, you must do so in writing during your Initial Enrollment Period. If Social Security is automatically enrolling you, you will receive a notice in the mail with instructions on how to decline — you have a important date to respond, usually about two weeks.

If you decline Part B and later want to enroll, you will face a late-enrollment penalty unless you had creditable coverage the whole time. The exception is if you are still working and covered by your employer's plan — you can enroll in Part B without penalty within eight months of leaving that job or losing that coverage.

Common Mistakes to Avoid

The biggest mistake is waiting past your Initial Enrollment Period without realizing you need to act. If you are not yet receiving Social Security, Social Security will not contact you — you must contact them. Mark your calendar three months before you turn 65 and enroll then, rather than waiting until the last month of your window.

Another common error is not reporting other coverage you have. If you are still working or covered by a spouse's employer plan, tell Medicare this when you enroll. It protects you from the late-enrollment penalty later. Do not assume Medicare knows about your coverage — you must tell them.

A third mistake is losing your Medicare card and not requesting a replacement. If your card is lost, stolen, or damaged, call 1-800-MEDICARE and request a new one. You need the card to show providers you have coverage.

Frequently Asked Questions

What if I turn 65 while still working?

You can delay Part B enrollment without penalty if you have health coverage through your current job. You have eight months after you leave that job or lose that coverage to enroll in Part B without owing a late-enrollment penalty. Tell Medicare about your employer coverage when you enroll so they document this.

Can I enroll in Part B after I turn 65 if I missed my Initial Enrollment Period?

Yes, you can enroll during the General Enrollment Period, which runs January 1 through March 31 each year. Coverage starts July 1. However, you will owe a late-enrollment penalty unless you had creditable coverage during the time you were not enrolled.

Do I have to enroll in Part B if I have Medicare Part A?

No. Part A and Part B are separate. You can have Part A without Part B. However, if you decline Part B and later want it, you will owe a permanent penalty unless you had other coverage the whole time or may have access to for a Special Enrollment Period.

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

You must be a U.S. citizen or a lawful permanent resident who has lived in the United States for at least five consecutive years to enroll in Medicare. Bring proof of legal residency — a green card, visa, or naturalization papers — when you enroll.

How much does Part B cost?

The standard Part B premium changes each year. For 2024, the standard premium is $164.90 per month, but higher earners pay more based on income from two years prior. Medicare will tell you your exact premium when you receive your card. You may also owe an annual deductible and copayments when you use services.