For the vast majority of Americans who look forward to receiving Medicare health benefits, eligibility is as uncomplicated as celebrating your 65th birthday.
But your eligibility to receive premium-free Medicare Part A – and your eligibility for other Medicare plans – depends on such factors as your work history and the plan options that are available where you live. And if you’re applying for Medigap after your Medigap open enrollment period ends, your medical history could also be a factor. Here’s what you need to know:
Am I eligible for Medicare Part A?
Generally, you’re eligible for Medicare Part A if you’re 65 years old and either a U.S. citizen or you have been a legal resident of the United States for at least five years. If you’re already collecting Social Security or Railroad Retirement Board benefits, you’ll be automatically enrolled in premium-free Part A. Your Medicare card should automatically arrive in the mail about three months prior to your 65th birthday (or the 25th month of a disability, if you’re qualifying due to disability rather than age).
If you’re not already receiving Social Security or Railroad Retirement benefits, you’ll need to enroll in Medicare during the seven-month Initial Enrollment Period (IEP), which includes the three months before the month you turn 65, the month you turn 65, and the three following months. If you enroll before the month you turn 65, your benefits will start the month you turn 65 (or the month before, if your birthday is on the first of the month). If you enroll in the three months after you turn 65, your Part B coverage won’t take effect until the month after you complete your enrollment.
In addition to turning 65, people can become eligible for Medicare due to a disability (eligibility for Medicare starts after they’ve been receiving Social Security or Railroad Retirement Board disability benefits for two years), or due to end-stage renal disease (ESRD) or amyotrophic lateral sclerosis (ALS).
People with ESRD become eligible for Medicare on the fourth month of dialysis treatment, or earlier if they take part in home-dialysis training. People with ALS become eligible for Medicare the same month their disability benefits begin (and there’s no longer a five-month waiting period for disability benefits to begin after a person is diagnosed with ALS).
Am I eligible for Medicare Part B?
When you receive notification that you’re eligible for Medicare Part A, you’ll also be notified that you’re eligible for Medicare Part B. But unlike Part A – which is premium-free for almost all enrollees – Part B has a monthly premium.
If you’re already receiving Social Security benefits, your enrollment in Part B will be automatic, although you are not obligated to accept the enrollment.
If you’re not already receiving Social Security benefits, you’ll have the same enrollment window that you have for Part A – beginning three months prior to the month you turn 65 and continuing for three months afterward. And while you can enroll in the three months following your 65th birthday, your Part B coverage will be delayed until the month following your enrollment, which could leave you with a gap in health coverage. If you don’t enroll by the end of the seven-month window and don’t qualify for a special enrollment period, you’ll have to wait until hte next General Enrollment Period to sign up.
If you don’t enroll during your initial window, you won’t lose eligibility for Part B, but you will be penalized with an increased premium when you eventually enroll. This penalty causes your premium to increase by 10% for each year that you’re eligible but don’t enroll in Part B.
Note that there’s no penalty if you delay Part B because you’re covered by a current employer’s plan – either your own or your spouse’s. But this is not the case if you’re covered by retiree or COBRA coverage, or something other than employer-sponsored group health insurance. Those types of coverage will not allow you to avoid the late-enrollment penalty.
Am I eligible for Medicare Advantage?
If you’re eligible for Medicare benefits, you have to choose how to receive them – either through Original Medicare or through Medicare Advantage. Enrollment is split nearly equally between the two programs: As of mid-2025, there were 33.6 million people with Original Medicare, and 35.4 million with Medicare Advantage.
You need to have (or be eligible for) both Medicare Part A and Part B in order to enroll in Medicare Advantage, and you can select a plan during your Initial Enrollment Period. (Note that there are some rural areas of the country where Medicare Advantage plans are not available. You have to live in an area where Advantage plans are offered in order to enroll in one.)
Most Medicare Advantage plans also include Part D prescription drug coverage. So if you have a Medicare Advantage plan, you typically receive your Part D coverage together with the health and hospital benefits, in one single package.
Who's eligible for Medicare Part D prescription drug coverage?
To be eligible for Medicare Part D prescription drug coverage, you must have either Medicare Part A or Part B, or both. You can sign up for Medicare Part D at the same time that you enroll in Medicare Part A and B.
Most people who select Medicare Advantage must receive their Part D prescription benefits as part of that same Medicare Advantage plan. In 2025 only about 4% of all Medicare Advantage enrollees are in plans that don’t include Part D coverage.
However, Medicare Savings Account (MSA) plans do not include Part D coverage, nor do some Private Fee-for-Service (PFFS) Medicare plans. If you have an MSA or a PFFS and it doesn’t have Part D coverage included, you’re allowed to purchase a stand-alone Part D plan to supplement it.
As with Part B, you are still eligible for Part D prescription drug coverage if you don’t enroll when you’re first eligible, but you may pay higher premiums if you enroll later on, unless you had creditable coverage from another plan during the time that you delayed enrollment in Part D.
Who's eligible for Medigap (Medicare supplement insurance)?
If you’re enrolled in Original Medicare (both Medicare Part A and Part B), then you’re eligible to apply for a Medigap policy. These plans are standardized, and are designed to cover some or all of the out-of-pocket costs that are incurred when you have a Medicare-covered claim (meaning they pay some or all of your deductible, daily copays, and coinsurance).
You have a one-time, six-month Medigap open enrollment period that starts when you’re at least 65 years old and have enrolled in Part B. (You need both Part A and Part B to enroll in Medigap, though some people delay Part B enrollment while they’re still covered by active employee coverage. Their Medigap enrollment window begins when they enroll in Part B.)
After this time runs out, and depending on your medical history and where you live, you will have only limited chances to purchase Medigap coverage later on.
Some states allow people of any age or health status to purchase Medigap coverage at any time (or during a specific window each year) without medical underwriting, but most don’t. In some states, Medigap plans may not be available for people who have Medicare before age 65.
Most states require Medigap insurers to offer at least one plan to disabled Medicare beneficiaries under age 65. But depending on the state, the plan options can be limited and the premiums can be significantly higher than the premiums that are charged when an applicant is 65. This varies considerably from one state to another. You can check with the insurance department in your state to learn about your Medigap coverage options.
And unlike Medicare Advantage and Medicare Part D, federal rules do not provide any sort of annual enrollment or plan change window for Medigap.
But some states have created annual opportunities for people to enroll or switch plans, often linked with the enrollee’s birthday. Again, you can reach out to the insurance department in your state to see if your state offers an annual opportunity to switch your Medigap without medical underwriting.
To be clear, anyone with Original Medicare can apply for a Medigap policy at any time. But in most states, if you’re outside your initial six-month enrollment window and not eligible for a special enrollment period, the insurer will consider your medical history before deciding whether to accept you and at what price.
Read more about Medigap plan eligibility and enrollment.
Louise Norris is an individual health insurance broker who has been writing about health insurance and health reform since 2006. She has written hundreds of opinions and educational pieces about the Affordable Care Act and Medicare for healthinsurance.org and medicareresources.org.
