When and how to sign up for Part B coverage

You enroll in Medicare Part B during your Initial Enrollment Period, which runs for seven months: three months before the month you turn 65, the month you turn 65, and three months after. If you miss this window, you can still enroll during the General Enrollment Period (January 1 to March 31 each year), but you may pay a penalty for each month you delayed.

To enroll, you contact Social Security directly — by phone, online, or in person at a local office. You will need your Social Security number, proof of citizenship or legal residency, and information about any current health coverage. Social Security handles the enrollment; you do not go through Medicare itself to sign up for Part B.

If you are already receiving Social Security benefits when you turn 65, you are usually enrolled in Part B automatically. If you are not yet taking Social Security, you must contact Social Security to enroll in Part B separately, even if you have already enrolled in Part A (hospital coverage).

Key Takeaways

  • Your Initial Enrollment Period is seven months long: three months before you turn 65, the month of your birthday, and three months after.
  • You enroll through Social Security by phone (1-800-772-1213), online at ssa.gov, or at your local Social Security office — not through Medicare directly.
  • If you delay enrollment past your Initial Enrollment Period without a valid reason, you will pay a higher Part B premium for as long as you have Medicare.
  • If you are already receiving Social Security at 65, Part B enrollment happens automatically; if not, you must contact Social Security yourself.
  • You will need your Social Security number, proof of citizenship or legal residency, and details about any current health insurance.

What happens if you miss your Initial Enrollment Period

If you do not enroll during your seven-month Initial Enrollment Period and you do not have a valid reason for the delay, you will owe a late enrollment penalty. This penalty is a percentage added to your Part B premium, and it stays with you for as long as you have Medicare — it does not go away after a few years.

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 delayed for two years, for example, your premium would be 20 percent higher than the standard amount. The exact dollar amount changes each year because the base premium changes.

You can still enroll during the General Enrollment Period (January 1 to March 31), and your coverage will start July 1 of that year. However, you will owe the penalty unless you had a valid reason for missing your Initial Enrollment Period — such as being covered by a current employer's health plan or being a federal employee.

Exceptions that let you enroll without a penalty

You can enroll in Part B after your Initial Enrollment Period without owing a penalty if you have creditable coverage — health insurance through a current employer, a spouse's employer, TRICARE (military coverage), or the Veterans Health Administration. You must enroll within eight months of losing that coverage to avoid the penalty.

If you are a federal employee or a railroad retiree, different rules explore. Federal employees can enroll in Part B during a special enrollment window after they retire or lose their coverage. Railroad retirees should contact the Railroad Retirement Board to understand their enrollment timeline.

If you believe you have a valid reason for missing your important date, you can request that Social Security waive or reduce your penalty. You will need to provide documentation of your reason — such as a letter from your employer confirming you were covered under their plan. Contact Social Security to discuss your situation.

Enrollment steps and what to expect

Start by gathering your documents: your Social Security number, proof of U.S. citizenship or legal residency (passport, birth certificate, or naturalization papers), and information about any health coverage you currently have. If you are married and your spouse is also enrolling, bring their documents too.

Call Social Security at 1-800-772-1213 (TTY 1-800-325-0778 for deaf and hard of hearing callers). You can also visit ssa.gov to create an account and enroll online, or go to your local Social Security office in person. The phone line is open Monday through Friday, 7 a.m. to 7 p.m. your local time.

During the call or visit, a Social Security representative will confirm your identity, verify your citizenship or residency status, and ask about any current health coverage. They will enroll you in Part B and provide you with a confirmation number. Your coverage typically begins on the first day of the month after you enroll, though the exact date depends on when you contact Social Security.

Understanding Part B costs and what is covered

Part B has a monthly premium (the amount you pay each month), an annual deductible (the amount you pay out of pocket before coverage begins), and copayments or coinsurance for services. The premium amount changes each year; you can find the current year's premium on Medicare.gov or by calling 1-800-MEDICARE.

Part B covers doctor visits, outpatient hospital services, medical equipment, and preventive care like screenings and vaccines. It does not cover dental, vision, or hearing services — those require separate coverage. If you want broader coverage, you can enroll in a Medigap plan or a Medicare Advantage plan after you have Part B.

If your income is below a certain level, you may be able to get help paying your Part B premium through a program called Medicaid or the Medicare Savings Program. Contact your state Medicaid office or call 1-800-MEDICARE to learn whether you may have access to.

Coordinating Part B with other coverage

If you are still working and covered by your employer's health plan, you can delay enrolling in Part B without a penalty — but only if your employer has 20 or more employees. Once you leave that job or lose the coverage, you have eight months to enroll in Part B without owing a penalty.

If you are covered by TRICARE (military health coverage) or the Veterans Health Administration, you also have a special enrollment window. Tell Social Security about your military or veteran status when you enroll; they will make sure your enrollment is timed correctly to avoid penalties.

If you enroll in a Medicare Advantage plan (Part C), you are automatically enrolled in Part B as well — you cannot have Part C without Part B. If you later switch back to Original Medicare (Part A and Part B), you can enroll in a Medigap plan during your Medigap open enrollment period.

Frequently Asked Questions

Can I enroll in Part B online or do I have to call Social Security?

You can enroll online through your Social Security account at ssa.gov, by phone at 1-800-772-1213, or in person at a local Social Security office. Online enrollment is available 24 hours a day. The phone line is open Monday through Friday, 7 a.m. to 7 p.m. your local time.

What if I am not yet receiving Social Security benefits?

You must contact Social Security to enroll in Part B even if you have not started taking Social Security retirement benefits. You can enroll online, by phone, or in person. Social Security will set up your Part B coverage separately from any retirement benefits you may claim later.

When does my Part B coverage start after I enroll?

Coverage typically begins on the first day of the month after you enroll. If you enroll in March, for example, your coverage would start April 1. The exact date depends on when Social Security processes your enrollment, so ask for confirmation when you sign up.

What documents do I need to bring to enroll?

Bring your Social Security number, proof of U.S. citizenship or legal residency (passport, birth certificate, or naturalization papers), and information about any current health coverage. If you are enrolling by phone or online, you will need to provide this information verbally or type it in.

Do I have to pay the Part B premium right away?

Your first Part B premium is usually deducted from your Social Security check if you are receiving benefits. If you are not yet taking Social Security, Social Security will send you a bill. Premiums are due by the 30th of each month to keep your coverage active.