When and How to Enroll in Part B

You sign up for 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 later, but you will pay a permanent penalty on your monthly premium unless you have a valid reason for the delay.

The three ways to sign up are: online at Medicare.gov, by phone at 1-800-MEDICARE (1-800-633-4227), or in person at your local Social Security office. Online enrollment takes about 10 minutes. Phone enrollment takes longer because the representative will ask for your information verbally, but it is useful if you have questions during the process. In-person enrollment at Social Security is slowest but gives you a paper record on the spot.

You will need your Social Security number, proof of citizenship or legal residency, and information about any current health coverage you have. If you are still working and covered by an employer plan, tell Medicare — this affects when your Part B coverage starts and whether you owe a penalty later.

Key Takeaways

  • Your Initial Enrollment Period is seven months long: three months before you turn 65, the month you turn 65, and three months after.
  • You can enroll online at Medicare.gov, by phone at 1-800-MEDICARE, or in person at your local Social Security office.
  • If you miss your Initial Enrollment Period and do not have employer coverage or another valid reason, you will pay a permanent 10 percent penalty on your Part B premium for as long as you have Medicare.
  • Part B coverage normally starts the first day of the month after you enroll, unless you enroll during your birth month, in which case it can start the first of that month.

What Documents You Need to Bring or Have Ready

Before you start, gather your Social Security number, birth certificate or passport, and proof of U.S. citizenship or legal residency. If you were born outside the United States, you will also need a green card or other immigration document showing you are a lawful permanent resident.

Have your current insurance information on hand. This includes the name of your employer if you are still working, the name of any health plan you are covered by, and your policy or group number. If you are on Medicaid or have coverage through a spouse's employer, Medicare needs to know that too. This information determines whether you owe a late enrollment penalty and when your coverage actually begins.

Enrolling Online at Medicare.gov

Go to Medicare.gov and click "Create an Account" if you do not already have one. You will set up a username and password, then answer security questions. This account lets you manage your Medicare information anytime without calling.

Once logged in, select "Enroll in Medicare Part B" from the menu. You will enter your personal information, Social Security number, and citizenship status. The system will ask about any current health coverage — answer honestly, because lying about employer coverage or other insurance can delay your enrollment or create problems later.

Review the summary page, then submit. You will see a confirmation number on screen and receive an email with the same number. Save or print this — you may need it if you call Medicare with questions. Part B coverage normally starts on the first day of the month after you enroll.

Enrolling by Phone or in Person

Call 1-800-MEDICARE (1-800-633-4227) Monday through Friday, 8 a.m. to 8 p.m. Eastern time. Have your Social Security number and citizenship information ready. The representative will walk you through the same questions as the online form, then mail you a confirmation letter within two weeks.

To enroll in person, visit your local Social Security office. You can find the nearest one at ssa.gov or by calling 1-800-772-1213. Bring your Social Security card, birth certificate or passport, and proof of citizenship. The office will process your enrollment on the spot and give you a receipt. This method is slower — Social Security offices often have wait times of 30 minutes to two hours — but you leave with proof in hand.

What Happens After You Enroll

Medicare will mail you a Medicare card within two weeks of enrollment. This card shows your Medicare number, the date your coverage starts, and which parts of Medicare you have. Keep it in a safe place — you will need it when you see doctors or fill prescriptions.

Your Part B coverage normally starts on the first day of the month after you enroll. If you enroll during your birth month, coverage can start the first of that month instead. You will begin paying the monthly Part B premium (the amount changes each year) starting with your first month of coverage. The premium is usually taken directly from your Social Security check, but you can choose to pay by mail or bank draft instead.

Once you have Part B, you can choose how to get the rest of your coverage. You can stay with Original Medicare and add a Medigap policy, or you can switch to a Medicare Advantage plan. You have two months after Part B starts to make this choice without penalty.

Late Enrollment Penalties and How to Avoid Them

If you do not enroll in Part B during your Initial Enrollment Period, Medicare charges a late enrollment penalty of 10 percent of the standard Part B premium for each full 12 months you were may be able to access but not enrolled. This penalty is permanent — you pay it for as long as you have Medicare, even if you enroll years later.

You can avoid the penalty if you have a valid reason for missing the important date. The main exceptions are: you were covered by an employer health plan while you or your spouse was still working, you were covered by TRICARE (military health coverage), or you were living outside the United States and covered by a U.S. health plan. You must show proof of this coverage when you enroll.

If you think you have a valid reason, tell Medicare when you enroll. Bring documentation — a letter from your employer, a copy of your health plan card, or a TRICARE statement. Medicare will review your case and decide whether to waive the penalty. This process takes several weeks, so enroll as soon as you realize you missed the important date.

Frequently Asked Questions

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

You can delay enrolling in Part B without penalty as long as you or your spouse is still working and you have coverage through that employer. When you or your spouse stops working, you have eight months to enroll in Part B without owing a late penalty. Tell Medicare about your employer coverage when you enroll so they know you may have access to for this exception.

Can I change my mind after I enroll?

Yes, but only during specific times. If you enroll during your Initial Enrollment Period, you can change your mind during the General Enrollment Period (January 1 to March 31 each year), and your new choice takes effect July 1. If you enroll in a Medicare Advantage plan instead of Original Medicare, you have one month to switch back to Original Medicare without penalty.

What if I miss my Initial Enrollment Period?

You can still enroll during the General Enrollment Period (January 1 to March 31), but your coverage will not start until July 1, and you will owe a permanent late penalty unless you have a valid reason for the delay. The sooner you enroll after missing your Initial Enrollment Period, the sooner your coverage begins.

Do I have to enroll in Part B if I am still working?

No, you can delay Part B if you have employer coverage through your job or your spouse's job. However, you must enroll within eight months of losing that coverage to avoid a permanent penalty. If you are self-employed or have coverage through a different source, you should enroll during your Initial Enrollment Period.

Will my Part B premium come out of my Social Security check?

Usually yes — Medicare automatically deducts the Part B premium from your Social Security benefit if you receive one. If you do not receive Social Security, Medicare will bill you directly by mail. You can request to pay by bank draft or check instead if you prefer, but you must set this up when you enroll or contact Medicare later to change it.