What Medicare Part B covers and when you can sign up

Medicare Part B is medical insurance that covers doctor visits, outpatient care, lab tests, and some medical equipment. Unlike Part A (hospital insurance), which most people get automatically at 65, you must take a separate step to enroll in Part B. The timing matters: if you miss your window, you may pay a higher premium for the rest of your life.

Your initial enrollment window opens three months before the month you turn 65 and closes three months after. If you sign up during this seven-month period, your coverage typically starts the first day of the month you turn 65. If you enroll after this window closes, your coverage starts the first day of the month after you sign up, and you will owe a penalty on top of your regular premium.

The main exception: if you or your spouse are still working and covered by an employer health plan, you may be able to delay Part B without penalty. This is called creditable coverage, and you will need to show proof when you do enroll.

Key Takeaways

  • You can enroll in Part B online through Medicare.gov, by phone at 1-800-MEDICARE, or in person at your local Social Security office.
  • Your initial enrollment window is seven months long: three months before, the month of, and three months after your 65th birthday.
  • If you enroll during your initial window, coverage usually starts on the first day of the month you turn 65; if you enroll late, coverage starts the month after you sign up.
  • Late enrollment penalties add 10 percent to your Part B premium for each full year you delayed, and this penalty is permanent.
  • If you have employer coverage or are a federal employee, you may be able to delay Part B without penalty as long as you enroll within eight months of losing that coverage.

Enrolling online through Medicare.gov

The fastest way to enroll is through Medicare.gov, the official Medicare website. Go to Medicare.gov, select "Sign up for Medicare" or "Manage your Medicare," and log in with your username and password. If you do not have an account, you can create one using your email address and a password you choose.

Once logged in, look for the option to enroll in Part B. You will need your Social Security number, date of birth, and citizenship or immigration status. The form asks whether you want to enroll in Part B, Part D (prescription drug coverage), or both. You can also choose whether to have your premium deducted from your Social Security check or receive a bill by mail. After you submit, you should see a confirmation number on screen and receive an email confirmation.

Processing typically takes about two weeks. You can check the status of your enrollment by logging back into Medicare.gov and viewing your process history.

Enrolling by phone or in person

If you prefer to enroll over the phone, call 1-800-MEDICARE (1-800-633-4227). Representatives are available Monday through Friday, 8 a.m. to 8 p.m. Eastern time, and Saturday, 9 a.m. to 1 p.m. Eastern time. Have your Social Security number, date of birth, and citizenship information ready. The representative will walk you through the enrollment form and can answer questions about your coverage options.

You can also enroll in person at your local Social Security office. Find the nearest office by visiting ssa.gov/locator or calling 1-800-772-1213. Bring your Social Security card, proof of citizenship (passport, birth certificate, or naturalization papers), and proof of residency (utility bill or lease). An employee will help you complete the enrollment form and can answer questions about Part B coverage and costs.

What information you will need to provide

Before you start, gather these documents:

  • Your Social Security number
  • Proof of U.S. citizenship or legal residency (passport, birth certificate, green card, or naturalization papers)
  • Proof of residency in the United States (utility bill, lease, mortgage statement, or bank statement dated within the last two months)
  • If you have employer coverage or are a federal employee, the name of your employer and the date your coverage ends or ended

If you are enrolling online, you will not need to upload documents; you will straightforward enter the information. If you enroll by phone or in person, have these documents nearby so you can answer questions about them.

Understanding Part B costs and coverage start dates

The standard Part B premium changes each year. The amount you pay depends on your income from two years ago; higher earners pay more. You will receive a notice in the mail showing your premium amount before your coverage starts.

Your coverage start date depends on when you enroll. If you enroll during your initial seven-month window (three months before through three months after your 65th birthday), coverage usually begins on the first day of the month you turn 65, even if you enroll later in that window. If you enroll after your initial window closes, coverage starts the first day of the month after you submit your enrollment.

You can choose to have your premium deducted automatically from your Social Security check, or you can pay by mail. If you choose automatic deduction, the first payment is usually taken from your Social Security check in the month your coverage starts.

What happens if you miss your enrollment important date

If you do not enroll during your initial seven-month window and you do not have creditable coverage (employer or federal employee health insurance), you will owe a late enrollment penalty. This penalty is 10 percent of the standard Part B premium for each full year you delayed enrollment. The penalty is permanent and stays with you for as long as you have Part B.

For example, if you turn 65 in January 2024 and do not enroll until January 2026 (two years late), you would owe a penalty equal to 20 percent of the standard premium, added to your monthly bill for life. There is no way to remove this penalty once it is applied.

The only way to avoid the penalty is to show that you had creditable coverage during the time you were not enrolled in Part B. Creditable coverage includes employer health insurance, federal employee health insurance, TRICARE (military coverage), or certain other group health plans. You will need to provide documentation from your employer or plan showing the dates you were covered.

Frequently Asked Questions

Can I enroll in Part B after I turn 65 if I am still working?

Yes, but only if your employer or your spouse's employer offers health insurance and you are enrolled in it. This is called creditable coverage. You can delay Part B without penalty as long as you enroll within eight months after your coverage ends or you stop working, whichever comes first. When you do enroll, bring a letter from your employer stating the dates you were covered.

What if I enrolled in Part A but not Part B?

You can enroll in Part B at any time by contacting Medicare through the methods listed above. If you enroll after your initial window, you will owe a late enrollment penalty unless you had creditable coverage. Your coverage will start the first day of the month after you enroll.

Do I have to enroll in Part D at the same time as Part B?

No. You can enroll in Part B and Part D separately. However, if you do not enroll in Part D when you first become may be able to access and you do not have creditable prescription drug coverage, you will owe a late enrollment penalty on your Part D premium as well. It is often simpler to enroll in both at the same time, but you can choose to do them separately.

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

You can enroll in Part B if you are a lawful permanent resident (green card holder) and have lived in the United States for at least five years. You will need to provide your green card and proof of residency. If you have questions about your immigration status and may be able to access, call 1-800-MEDICARE and ask to speak with a representative who handles non-citizen cases.

Can I change my mind after I enroll in Part B?

Yes, but only during specific times. You can disenroll from Part B during the General Enrollment Period (January 1 through March 31 each year), and your coverage will end on June 30. However, if you disenroll, you may owe a late enrollment penalty if you enroll again later. Talk to a Medicare representative before you disenroll to understand the consequences.