How to Sign Up for Medicare Part B

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 — 10 percent more for each full year you delayed.

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 is fastest — you can complete it in about 15 minutes if you have your Social Security number and birth date ready. Phone enrollment takes longer because the representative will ask verification questions, but you get when ready confirmation of your enrollment date.

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. If you enroll after that window closes, there is a delay: coverage begins the first day of the month after the month you enroll.

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 at a Social Security office — online is the fastest option.
If you miss your Initial Enrollment Period, you will pay a 10 percent higher monthly premium for each year you delayed, and this penalty stays with you permanently.
Part B coverage begins on the first day of the month after you enroll, or the first day of the month you turn 65 if you enroll on time.
You will need to pay a monthly premium for Part B; the amount changes each year and depends on your income.

What Documents and Information You Need

Before you start, gather your Social Security number, date of birth, and Medicare number if you already have one. You will also need proof of U.S. citizenship or lawful permanent resident status — a birth certificate, passport, or naturalization papers work. If you are enrolling by phone or in person, bring these documents with you; online enrollment asks you to enter the information directly.

If you are still working and have health insurance through your employer, bring your insurance card or a letter from your employer stating your coverage dates. This matters because if your employer has 20 or more employees, you may be able to delay Part B without penalty — a rule called creditable coverage. You will need to prove this coverage when you eventually enroll.

Understanding Part B Costs and Income-Related Premiums

Part B has a monthly premium that you pay to Medicare. The standard premium amount changes each year; in recent years it has ranged from roughly $160 to $175 per month, but confirm the current amount at Medicare.gov because it shifts annually. You also pay a yearly deductible before Medicare starts to cover your doctor visits and outpatient services — this deductible also changes yearly.

If your income is above a certain threshold, you will pay an Income-Related Monthly Adjustment Amount (IRMAA) on top of the standard premium. Medicare uses your tax return from two years prior to calculate this. For example, if you enroll in 2025, Medicare looks at your 2023 income. If your income was high in 2023 but has dropped since, you can request a reduction in your IRMAA by submitting a form and proof of your changed circumstances.

Enrolling If You Missed Your Initial Period

If you did not enroll during your Initial Enrollment Period and you are not still covered by an employer plan, you can enroll during the General Enrollment Period, which runs from January 1 to March 31 each year. Coverage begins July 1 of that year. You will owe the 10 percent annual penalty on your premium for as long as you have Part B.

There is one exception: if you were covered by an employer health plan when you turned 65 and you enroll in Part B within eight months of losing that coverage, you do not owe a penalty. This is called the Special Enrollment Period. You must have written proof that your employer coverage ended — a letter from your employer or your final insurance card works.

What Happens After You Enroll

After you enroll, Medicare will mail you a new Medicare card within two weeks that shows your Part B coverage. Your coverage becomes active on the date Medicare confirms, which is usually the first of the month after you enroll. If you enrolled during your Initial Enrollment Period (before or during the month you turn 65), coverage starts the first of the month you turn 65.

Your premium will be deducted from your Social Security check each month, or Medicare will bill you directly if you do not receive Social Security. You can change how you pay by contacting Medicare. If you also want to enroll in Part D (prescription drug coverage) or a Medigap or Medicare Advantage plan, you can do that at the same time or later — but enrolling in Part D within 63 days of Part B helps you avoid a penalty on your drug coverage.

Common Mistakes to Avoid

The biggest mistake is waiting too long. If you turn 65 and do not enroll in Part B right away, and you do not have creditable coverage through an employer, you will owe a penalty for every month you were late. This penalty is permanent — it does not go away even after you finally enroll. Calculate the cost: 10 percent per year adds up quickly if you wait five or ten years.

A second mistake is not reporting a change in income. If your income drops after you enroll and you are paying an IRMAA, contact Medicare to request a recalculation. You will need to submit a form (SSA-44 or similar) and proof of the change — a recent tax return, a letter from your employer, or a notice of reduced benefits. Without this, you will overpay for months or years.

A third mistake is confusing Part B with Part A. Part A covers hospital stays and is usually free if you or your spouse paid Medicare taxes while working. Part B covers doctor visits and outpatient care and requires a monthly premium. You need both for full coverage, but they enroll separately.

Where to Get Help

Medicare.gov has an enrollment tool that walks you through the process step by step. You can also call 1-800-MEDICARE to speak with a representative who can answer questions before you enroll. If you need in-person help, visit your local Social Security office — no appointment is needed, though wait times vary.

If you are low-income, you may be able to get help paying your Part B premium through a program called Medicaid or the Medicare Savings Program. Your state Medicaid office can tell you whether you may have access to. You can find your state office through Medicaid.gov.

Frequently Asked Questions

What if I am still working at 65 — do I have to enroll in Part B?

Not when ready, if your employer has 20 or more employees and you are covered by their health plan. You can delay Part B without penalty as long as you are actively employed and covered. When you leave your job, you have eight months to enroll without owing a penalty. After eight months, the penalty applies.

Can I enroll in Part B without enrolling in Part A?

Yes, but it is unusual. Most people are automatically enrolled in Part A at 65 if they or their spouse paid Medicare taxes. If you want Part B but not Part A, you can request that during enrollment. However, Part A is usually free, so most people keep both.

What if I enroll online but do not receive my Medicare card?

Medicare mails cards within two weeks of enrollment. If you do not receive yours within three weeks, call 1-800-MEDICARE to confirm your address and request a replacement. You can also check your enrollment status on Medicare.gov by signing into your account.

Do I have to pay the Part B premium every month?

Yes. Part B requires a monthly premium for as long as you have it. The amount is deducted from your Social Security check or billed to you directly. You can stop Part B coverage if you choose, but you will owe a penalty if you enroll again later, unless you have a may have access to reason.

What if my income changes after I enroll?

Contact Medicare within 60 days of the change. You will need to submit a form and proof — a recent tax return, a letter from your employer, or a notice of reduced benefits. Medicare will recalculate your IRMAA and adjust your premium going forward.

This guide is for general information only and is not medical, financial, legal, or other professional advice. For decisions specific to your situation, consult a qualified professional. See our Editorial Policy.