How to Enroll in Medicare: A Step-by-Step Guide

To enroll in Medicare, you apply through the Social Security Administration (SSA), either automatically or with a short application, during a set window tied to your 65th birthday. Most people become eligible at 65, and how you enroll depends on whether you already receive Social Security benefits. Missing your enrollment window can trigger late enrollment penalties that follow you for as long as you have Medicare, so getting the timing right matters.

Medicare is the federal health insurance program run by the Centers for Medicare & Medicaid Services (CMS), an agency within the U.S. Department of Health and Human Services. It covers adults 65 and older, along with younger people who have certain disabilities, End-Stage Renal Disease (ESRD), or Amyotrophic Lateral Sclerosis (ALS). The program has four parts: Part A (hospital insurance), Part B (medical insurance), Part C (Medicare Advantage, sold by private insurers), and Part D (prescription drug coverage).

This guide covers how to enroll in Medicare step by step, from your Initial Enrollment Period through choosing additional coverage, so you can make the decision on your own timeline. If you are turning 65 and exploring Medicare for the first time, start here.

According to CMS enrollment data, more than 65 million Americans were enrolled in Medicare in 2024, covering hospital, medical, and prescription drug benefits nationwide.

Who Is Eligible to Enroll in Medicare?

Most people become eligible for Medicare at age 65. You qualify for premium-free Part A if you or your spouse worked and paid Medicare taxes for at least 10 years (40 quarters). If you do not meet that work history requirement, you can still enroll in Part A by paying a monthly premium.

People under 65 may also qualify for Medicare in specific situations:

• Disability: If you have received Social Security Disability Insurance (SSDI) benefits for 24 consecutive months, you are automatically enrolled in Medicare Parts A and B.
• ALS (Lou Gehrig's Disease): You are enrolled in Medicare immediately upon receiving SSDI, with no waiting period.
• End-Stage Renal Disease (ESRD): permanent kidney failure requiring dialysis or a transplant, which qualifies you for Medicare at any age.

If you are approaching 65 for the first time, our turning 65 checklist walks through what to expect before your enrollment window opens.

Understanding Your Medicare Enrollment Windows

Initial Enrollment Period (IEP)

Your Initial Enrollment Period (IEP) is a seven-month window tied to your 65th birthday: the three months before your birthday month, your birthday month, and the three months after. According to Medicare.gov, when you enroll within this window affects when your coverage begins:

• Months 1-3 (before your birthday month): Coverage starts the first day of your birthday month.
• Month 4 (your birthday month): Coverage starts the first day of the following month.
• Months 5-7 (after your birthday month): Coverage starts one to two months after you enroll.

Enrolling in the three months before your birthday month gives you the earliest possible start date with no gap in coverage.

Special Enrollment Period (SEP)

A Special Enrollment Period (SEP) lets you delay Medicare Part B without penalty if you or your spouse are still working past 65 and covered by an employer or union group health plan. The SEP allows you to enroll in Part B any time while you have that coverage, plus eight months after it ends. COBRA and retiree coverage do not trigger an SEP. Review your situation with your employer's benefits office before delaying Part B, and see our guide on Medicare when you retire for how this applies if you plan to work past 65.

General Enrollment Period (GEP)

If you miss your IEP and do not qualify for an SEP, you can enroll during the General Enrollment Period (GEP), which runs January 1 through March 31 each year, with coverage beginning July 1. Missing your IEP and relying on the GEP means a gap in coverage and likely a permanent Medicare late enrollment penalty on your Part B premium.

What Happens After You Enroll in Parts A and B?

Once you have Original Medicare, you have three main directions for adding coverage.

Option 1: Add a Part D Drug Plan

Part D is standalone prescription drug coverage sold by private insurers and added to Original Medicare. Plans vary in cost, covered drugs (formulary), and pharmacy networks, so comparing options matters. If you do not sign up for Part D when first eligible and go without creditable drug coverage for 63 or more consecutive days, you may face a permanent Part D late enrollment penalty. Learn how this gap works in our guide to the Part D coverage gap.

Option 2: Add a Medicare Supplement (Medigap) Policy

Medigap plans, sold by private insurers, help pay the out-of-pocket costs Original Medicare does not cover, such as deductibles, coinsurance, and copayments. Your Medigap open enrollment window starts the month you are both 65 and enrolled in Part B, and lasts six months. During this window, insurers cannot deny you coverage or charge you more based on health conditions. Outside this window, medical underwriting may apply. Compare specific plan letters, such as Plan G and Plan N, to see what each covers.

Option 3: Switch to Medicare Advantage (Part C)

Medicare Advantage plans are offered by private insurers approved by CMS. They bundle Part A, Part B, and usually Part D into a single plan, and often include extra benefits like dental, vision, and hearing coverage. You must remain enrolled in both Part A and Part B to join a Medicare Advantage plan, and you generally cannot use a Medigap policy alongside it. See our comparison of Medicare Advantage vs. Medicare Supplement to weigh the tradeoffs. You can switch between Medicare Advantage and Original Medicare during the Medicare Annual Enrollment Period, which runs October 15 through December 7 each year, with changes taking effect January 1.

Medicare Savings Programs: Help With Costs

If your income and resources are limited, you may qualify for one of four Medicare Savings Programs administered by your state Medicaid office. According to Medicare.gov, these programs can pay some or all of your Medicare premiums, deductibles, coinsurance, and copayments:

• Qualified Medicare Beneficiary (QMB): Covers Part A and Part B premiums, deductibles, coinsurance, and copayments.
• Specified Low-Income Medicare Beneficiary (SLMB): Covers Part B premiums only.
• Qualifying Individual (QI): Covers Part B premiums only; funding is limited and applications are processed first-come, first-served each year.
• Qualified Disabled Working Individual (QDWI): Covers Part A premiums for certain working people with disabilities under 65.

Income and asset limits for these programs are set by each state and updated annually. Contact your state Medicaid office or call 1-800-MEDICARE to find out if you qualify and how to apply.