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-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 mail, or in person at a Social Security office. Most people are automatically enrolled in Part B when they turn 65 if they are already receiving Social Security benefits; if you are not automatically enrolled, you must take action yourself or face a permanent penalty on your premiums.

Part B covers doctor visits, outpatient care, lab tests, and medical equipment. It is not automatic — you choose whether to take it, and the choice you make at 65 affects your costs for life. If you delay enrollment without a valid reason, Medicare adds a 10 percent surcharge to your premium for each year you waited, and that surcharge stays on your bill permanently.

Key Takeaways

  • Your Initial Enrollment Period runs for seven months: three months before, the month you turn 65, and three months after.
  • You can enroll through Medicare.gov, by calling 1-800-MEDICARE, by mail, or at your local Social Security office.
  • If you are still working and have health insurance through your employer, you may be able to delay Part B without penalty — but you must report this to Medicare in writing.
  • Your Part B premium is deducted from your Social Security check each month, and the amount depends on your income from two years prior.
  • If you miss your enrollment window and do not have a valid reason, you will pay a permanent 10 percent surcharge on your premium for each year you delayed.

Documents and Information You Will Need

Gather your Social Security number, Medicare number (if you already have one), and proof of citizenship or legal residency before you start. You will also need to know your current health insurance situation — whether you have coverage through an employer, COBRA, or a spouse's plan — because this affects whether you can delay Part B without penalty.

If you are still working and want to delay Part B, you will need to provide written proof that you have health insurance through your job. This can be a letter from your employer's benefits department, your insurance card, or a benefits summary. Keep a copy for your records, because you may need to show it later if Medicare questions your delay.

The Three Ways to Enroll

Online at Medicare.gov: Go to Medicare.gov/sign-up, sign in with your username and password (or create an account), and follow the enrollment steps. This is the fastest route if you are comfortable online. You will get confirmation when ready, though it can take up to two weeks for your enrollment to show in Medicare's system.

By 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 on Saturday mornings. Have your Social Security number and current insurance information ready. The call usually takes 15 to 20 minutes. Ask for written confirmation to be mailed to you.

By mail or in person: read the CMS-40B form from Medicare.gov, fill it out, and mail it to your local Social Security office. You can also walk into any Social Security office with the form and enroll on the spot. Processing by mail takes two to four weeks. In person is faster — you get a receipt the same day.

What Happens After You Enroll

After you enroll, Medicare sends you a new or updated Medicare card in the mail within two weeks. Your Part B coverage starts on the first day of the month after you enroll, or on the first day of the month you turn 65 if you enroll during your Initial Enrollment Period. Your premium is deducted from your Social Security check starting the month your coverage begins.

If you do not receive your card within three weeks, call 1-800-MEDICARE to check the status. Do not wait — you need the card number to show your doctor and to set up prescriptions. Your premium amount is based on your income from two years before, so if your income was high two years ago, you may pay more now. You can request a review if your income has dropped significantly due to retirement or job loss.

If You Are Still Working: The Special Enrollment Rule

If you are still employed and have health insurance through your job, you can delay Part B without penalty. This is called the Special Enrollment Period for people with group health plan coverage. You do not have to enroll in Part B while you are working and covered by your employer's plan, even if you are over 65.

The catch: you must tell Medicare in writing that you are delaying because of employer coverage. Send a letter to your local Social Security office or Medicare stating your employer's name, your job status, and the dates of your coverage. Keep a copy. When you leave your job or lose the coverage, you have eight months to enroll in Part B without penalty. If you miss that window, the permanent surcharge applies.

Late Enrollment Penalties and How to Avoid Them

If you do not enroll during your Initial Enrollment Period and do not have a valid reason for the delay, Medicare charges you a permanent 10 percent surcharge on your Part B premium for each full year you waited. This surcharge never goes away — it stays on your bill for life. For example, if you delay three years, you pay 30 percent more than the standard premium, every month, forever.

Valid reasons to delay without penalty include having health insurance through an employer, COBRA, a spouse's plan, or certain government programs. You must document this coverage and report it to Medicare. If you missed your enrollment window by mistake, contact Medicare when ready to see if you can request a Special Enrollment Period. Some situations — like a life-changing event or a mistake by Social Security — may may have access to, but you have to ask.

Your Monthly Premium and How It Is Paid

Your Part B premium is deducted automatically from your Social Security check each month. The standard premium for 2024 is $164.90 per month, but this amount changes each year. If your income was over $97,000 (single) or $194,000 (married) two years ago, you pay a higher amount called an Income-Related Monthly Adjustment Amount, or IRMAA. The higher your income, the more you pay.

If you think your income has dropped since the amount was calculated, you can request a review. Send a letter to Social Security with proof of your income change — a tax return, a letter from your employer, or a benefits statement. The review can lower your premium retroactively, sometimes by several months. Do this as soon as your income drops; do not wait until the end of the year.

Frequently Asked Questions

What if I miss my Initial Enrollment Period?

You can still enroll, but you will owe a permanent 10 percent surcharge on your premium for each year you delayed, unless you have a valid reason like employer coverage. Contact Medicare when ready to see if you may have access to for a Special Enrollment Period. The sooner you enroll, the sooner the surcharge stops growing.

Do I have to take Part B if I am still working?

No. If you have health insurance through your job, you can delay Part B without penalty. You must notify Medicare in writing that you are delaying due to employer coverage. When you leave your job, you have eight months to enroll without penalty.

Can I change my mind after I enroll?

Yes, but only during the General Enrollment Period, which runs January 1 through March 31 each year. Changes take effect July 1. If you enrolled and want to drop Part B, you must submit a written request to Medicare. Dropping Part B may trigger a surcharge if you later re-enroll.

What if my Social Security check is not large enough to cover the premium?

If your Social Security benefit is very low, you may be able to pay your Part B premium directly to Medicare instead of having it deducted from your check. Contact Social Security to request this arrangement. You will receive a bill each month.

Does Part B cover everything my doctor does?

Part B covers doctor visits, lab tests, X-rays, and some medical equipment, but it does not cover prescription drugs, dental, vision, or hearing. You will need Part D for prescriptions and separate plans for dental and vision. Part B also requires you to pay a deductible and coinsurance for most services.