When and How to Sign Up for Part B Coverage

You enroll in Medicare Part B by contacting Social Security, Medicare, or your insurance agent during your enrollment window. Most people sign up when they turn 65, but the exact timing matters — if you miss your window, you pay a permanent penalty on your premiums. The three main enrollment periods are your Initial Enrollment Period (the seven months around your 65th birthday), the General Enrollment Period (January 1 to March 31 each year), and Special Enrollment Periods (if you have employer coverage or life changes).

You do not have to enroll in Part B if you are still working and covered by your employer's health plan, but you will need to sign up within eight months of leaving that job to avoid penalties. If you are already receiving Social Security benefits when you turn 65, Medicare will enroll you in Part B automatically — you can decline it, but you must do so actively.

Key Takeaways

  • Your Initial Enrollment Period runs for seven months: three months before the month you turn 65, the month itself, and three months after.
  • If you enroll after your Initial Enrollment Period ends, you pay a 10 percent permanent penalty on your Part B premium for each full year you delayed.
  • You can enroll through Social Security (online, by phone, or in person), Medicare.gov, or by calling 1-800-MEDICARE.
  • If you have employer health coverage, you can delay Part B without penalty as long as you enroll within eight months of losing that coverage.
  • Part B requires a monthly premium, a deductible, and coinsurance; the exact amounts change each year.

Your Three Enrollment Windows

Your Initial Enrollment Period is the most important window because it is the only one without a penalty. It spans seven months total: three months before the month you turn 65, the entire month you turn 65, and three months after. For example, if you turn 65 in June, your window opens March 1 and closes September 30. You should enroll as early as possible in this window so coverage starts on the first day of the month you turn 65 or the first day of the following month.

If you miss your Initial Enrollment Period, you can sign up during the General Enrollment Period, which runs January 1 through March 31 each year. Coverage begins July 1 of that year. However, you will owe a 10 percent penalty on your Part B premium for each full year you delayed. If you delayed for three years, your premium is 30 percent higher permanently — this penalty stays with you for life, even if you later switch plans.

A Special Enrollment Period lets you enroll without penalty if you have a may have access to life event. The most common reason is employer coverage: if you or your spouse are still working and covered by an employer plan, you can delay Part B. You have eight months from the date you lose that coverage (through retirement, job loss, or the employer dropping the plan) to enroll in Part B without penalty. Other may have access to events include moving out of your plan's service area, losing Medicaid, or gaining citizenship.

How to Enroll: Three Routes

The fastest route is usually Social Security. If you are not yet receiving Social Security benefits, you can visit your local Social Security office, call 1-800-772-1213, or go to ssa.gov to set up an account and enroll. You will need your Social Security number, proof of citizenship or legal residency, and information about any current health coverage. Social Security will ask whether you want Part B and whether you want to be enrolled in Original Medicare or a Medicare Advantage plan. If you are already receiving Social Security, you will be enrolled in Part B automatically at 65 unless you decline.

Medicare.gov is the official Medicare website. You can create an account, review your enrollment status, and make changes during your enrollment window. Call 1-800-MEDICARE (1-800-633-4227) if you need help navigating the site or have questions about your options. This line is available 24 hours a day, seven days a week, and staff can answer questions in many languages.

You can also work with a licensed insurance agent or broker who represents Medicare plans. They can walk you through your options and help you enroll at no cost to you — they are paid by the insurance company, not by you. Be cautious: some agents work for only one company, while others represent multiple plans. Ask whether they represent all plans in your area or just a few.

Documents and Information You Will Need

Before you enroll, gather these items. You will need your Social Security number, proof of U.S. citizenship or legal residency (a birth certificate, passport, naturalization papers, or permanent resident card), and information about any current health coverage (employer plan, COBRA, Medicaid, or Veterans benefits). If you have employer coverage, you will need the name of your employer or your spouse's employer and the date coverage began.

You will also need to decide whether you want Original Medicare (Part A and Part B, with the option to add Part D for prescriptions and Medigap for extra coverage) or a Medicare Advantage plan (an all-in-one alternative that includes Part A, Part B, and usually Part D). This choice is separate from enrolling in Part B itself — you are enrolling in Part B either way, but you are choosing how to receive your benefits. If you are unsure which is right for you, Medicare.gov has a plan comparison tool, or you can call 1-800-MEDICARE to talk through your options.

What Happens After You Enroll

Once you enroll, you will receive a Medicare card in the mail within two weeks. Your coverage usually starts on the first day of the month you turn 65 or the first day of the following month, depending on when you enroll. Check your card for errors — your name, date of birth, and Social Security number must be correct. If something is wrong, contact Social Security or Medicare right away.

Your Part B premium is deducted from your Social Security check each month if you are receiving benefits. If you are not yet receiving Social Security, Medicare will send you a bill. The premium amount changes each year; for 2024, the standard premium is $164.90 per month, but higher earners pay more through the Income-Related Monthly Adjustment Amount (IRMAA). You are also responsible for an annual deductible (currently $240) and coinsurance (usually 20 percent of the cost of covered services after you meet your deductible).

Penalties for Late Enrollment

If you enroll in Part B after your Initial Enrollment Period ends and you do not have a may have access to reason (like employer coverage), you pay a permanent 10 percent premium penalty for each full year you delayed. This penalty is calculated from the month your Initial Enrollment Period ended. For example, if your period ended in September 2023 and you enroll in March 2024, you delayed six months — not a full year — so no penalty applies. But if you enroll in October 2024, you delayed one full year, and your premium is 10 percent higher forever.

The only exception is if you have employer coverage or coverage through your spouse's employer. In that case, you can delay Part B without penalty as long as you enroll within eight months of losing that coverage. You must be able to prove you had employer coverage — your employer's benefits office can provide a letter stating the dates you were covered. If you miss the eight-month window, the penalty applies.

Special Situations: Employer Coverage and Automatic Enrollment

If you are still working at 65 and covered by your employer's health plan, you do not have to enroll in Part B. You can stay on your employer plan and delay Part B. However, you must enroll in Part B within eight months of retiring or losing that coverage. Your employer's benefits office can tell you the exact date your coverage ends — use that date to calculate your eight-month window. If you miss it, you owe the permanent penalty.

If you are already receiving Social Security when you turn 65, Social Security will enroll you in Part B automatically. Your Part B premium will be deducted from your monthly benefit. You can decline Part B by contacting Social Security before your coverage starts, but you must do this actively — silence counts as acceptance. If you decline and later change your mind, you will face the late enrollment penalty unless you have a may have access to reason.

Frequently Asked Questions

What if I turn 65 while still working?

You do not have to enroll in Part B while you are covered by your employer's health plan. You can delay enrollment and sign up within eight months of retiring or losing that coverage without penalty. Contact your employer's benefits office to confirm your coverage end date.

Can I enroll in Part B online?

Yes, through Medicare.gov or by creating a Social Security account at ssa.gov. You can also call 1-800-MEDICARE or visit a local Social Security office. Online enrollment usually takes 10 to 15 minutes.

What is the penalty for enrolling late?

You pay a 10 percent permanent increase to your Part B premium for each full year you delayed past your Initial Enrollment Period. This penalty stays with you for life. The only exception is if you had employer coverage and enroll within eight months of losing it.

Do I have to take Part B if I do not want it?

No. You can decline Part B, but you must do so in writing. If you are automatically enrolled through Social Security, contact Social Security before your coverage starts. If you decline and later want to enroll, you will owe the late enrollment penalty unless you have a may have access to reason.

When does my Part B coverage start?

Coverage usually begins the first day of the month you turn 65 or the first day of the following month, depending on when you enroll. If you enroll during the General Enrollment Period (January through March), coverage starts July 1 of that year.