If you’ve just celebrated your 65th birthday or it’s coming up in the next year, your mailbox is probably full of postcards, flyers and letters about your eligibility for Medicare.
It’s important to understand the ins and outs of Medicare before you sign up to avoid unexpected costs. Even if you’ve been on Medicare for years, you may want to reevaluate your options annually to confirm that your plan is still the best choice for you.
In this guide, we outline everything you need to know about what Medicare is, how it works and when you can sign up.
[READ: When and How to Change Your Medicare Plan]
What Is Medicare?
Simply put, Medicare is a federal health insurance program for those aged 65 and older. Medicare also covers those under the age of 65 with disabilities, as well as people with end-stage renal disease or amyotrophic lateral sclerosis (also known as Lou Gehrig’s disease).
Medicare Eligibility and Enrollment
Regardless of your retirement age, and if you qualify, you become eligible for Medicare when you turn 65.
Medicare initial enrollment
You can sign up for Medicare, specifically Part A and Part B, known as “original Medicare,” three months before your 65th birthday, during your birth month or throughout the three months after. You then have 60 days to sign up for Medicare Part D plans (more on that below). This overall window is known as the initial enrollment period. You may face a long-term penalty if you don’t sign up during these seven months, even if you’re still working.
Individuals receiving benefits four months before their 65th birthday from Social Security or the Railroad Retirement Board will be automatically enrolled in Medicare.
Medicare open enrollment
For those who aren’t enrolling for the first time, the open enrollment period, also known as the annual election period, runs from October 15 through December 7. During this period, you can:
— Review, adjust or switch your Medicare plans, including Medicare Part D or Medicare Advantage plans
— Enroll in a Medicare Advantage plan
— Drop a Medicare Advantage plan to return to original Medicare
However, if you’re switching back to original Medicare from a Medicare Advantage plan, you’ll likely be subject to underwriting, meaning the plan can review your medical history to determine whether you’re eligible and, if so, what you’ll pay for coverage. Coverage begins January 1 of the following year, according to Medicare.gov.
Another open enrollment period, known as the Medicare Advantage open enrollment period, runs from January 1 through March 31. This period is for those already enrolled in a Medicare Advantage plan who want to switch to another Medicare Advantage plan or go back to original Medicare.
Medicare general enrollment
The general enrollment period for Medicare, which lasts from January 1 through March 31, is for those who need to enroll in original Medicare but missed the initial enrollment window and don’t qualify for special enrollment (more on that below). Your coverage starts the month after you sign up. You might pay a monthly late enrollment penalty if you don’t qualify for a special enrollment period.
Medicare special enrollment
If you need to enroll or adjust your coverage outside of the regular enrollment windows, you may qualify for a special enrollment period. Some example situations include:
— You lost Medicare or Medicaid coverage after January 1.
— You couldn’t enroll because of a natural disaster or an emergency that’s declared or starts on or after January 1st..
— You’re volunteering and serving in another country.
— You were recently incarcerated and couldn’t sign up during your incarceration.
Depending on your situation, you may have up to six months to enroll in Medicare. If you don’t sign up within that window, you’ll have to wait for the general enrollment period and possibly pay a late enrollment penalty.
[Read: Medicare Allowances Explained: Allowable Rates and Benefits]
Medicare Plans and Coverage
There is a virtual alphabet soup of Medicare plans. Here are the parts that you need to know:
— Part A covers inpatient care in hospitals, skilled nursing, hospice and some home health care.
— Part B covers doctor visits, preventive care, outpatient care and hospitals, durable medical equipment and some home health care.
— Part D covers prescription drugs.
[READ: How Medicare Part D Has Changed for 2025]
Medicare Advantage vs. Medicare
In addition to Medicare Parts A, B and D, there’s an additional letter in the Medicare alphabet soup: Medicare Part C, also known as Medicare Advantage.
What is Medicare Advantage?
Medicare Advantage comprises health plans offered by private companies that contract with Medicare to provide you with all your Part A and Part B benefits. Most plans also offer Part D drug coverage. Premiums range by region and plan.
What does Medicare Advantage cover?
Medicare Advantage provides the same coverage as original Medicare (Part A and Part B), as well as some dental, vision and hearing coverage. Some Medicare Advantage plans may also include wellness coverage, such as gym memberships, and some over-the-counter drug coverage not provided in Part D. Plans can vary, though, so you’ll need to read the fine print to make sure your needs are covered.
What does Medicare Advantage not cover?
Medicare Advantage plans may have certain restrictions for covering medical care needed outside of the U.S. Make sure to review this benefit thoroughly before enrolling.
Who should get Medicare Advantage vs. Medicare?
Choosing original Medicare or a Medicare Advantage plan is a big decision, says Meredith Ramsey, an independent insurance agent in New Orleans.
“Medicare Advantage plans can have low or no monthly premiums, but they usually require members to get their care only from network doctors and hospitals,” she points out. “Both options may have deductibles, co-pays and coinsurance, where you pay a percentage of the bill.”
In 2025, Medicare Advantage plans have a maximum out-of-pocket limit of up to $9,350 for in-network services, according to the National Council on Aging. If your Medicare Advantage plan includes Part D prescription drug coverage, there is an additional $2,000 maximum out-of-pocket limit applied toward drug costs for 2025. Original Medicare, on the other hand, provides no cap on out-of-pocket expenses for hospital or outpatient services (though the Part D cap still applies if you’re enrolled in that plan).
With Medicare Advantage, you’ll also have access to fewer doctors and hospitals. For those who can’t afford to purchase a Medigap supplement to help cover the costs of original Medicare and who don’t mind adhering to a limited network of providers, a Medicare Advantage plan will likely be the best option.
For those who can’t afford to purchase a Medicare supplement plan to help cover the costs of original Medicare (more on that below) and who are willing to work within a limited provider network, as well as with referral and preauthorization requirements, a Medicare Advantage plan may be a good option.
How to sign up for Medicare Advantage
You can sign up for a Medicare Advantage plan in several ways:
— With the help of an individual, licensed insurance agent, who can enroll you via a paper or electronic application
— Through Medicare.gov
— By calling 1-800-MEDICARE (1-800-633-4227)
— Through a private insurer’s website (make sure to look for Medicare Advantage-specific plans)
Medicare Supplement (Medigap) Plans
If you’re opting for original Medicare but may need additional financial assistance to pay for out-of-pocket costs, you might consider a Medicare supplement plan.
What is a Medicare supplement plan?
A Medicare supplement plan, also known as Medigap, is for people who have original Medicare but need an additional plan to cover services and medications that fall under Medicare Part B.
Depending on where you live and when you’re eligible for Medicare, multiple types of Medigap policies, such as Medicare Plan G and Plan N, are offered by private insurers or via groups such as AARP. Costs vary considerably.
“You can go through your life with just parts A and B, but the out-of-pocket costs will get you,” notes Diane J. Omdahl, founder of 65 Incorporated, a Wisconsin-based company that helps people choose Medicare coverage.
With a Medigap policy, however, many of those costs are covered.
What does Medigap cover?
Medigap helps cover original Medicare-related costs, including:
— Deductibles
— Co-payments
— Coinsurance
What does Medigap not cover?
Medigap doesn’t cover:
— Vision care and glasses
— Dental care
— Hearing aids
— Long-term care, such as a nursing home
— Custodial care
Who should get a Medigap plan?
You should get a Medigap plan if you need to manage out-of-pocket costs associated with Medicare. A Medigap plan can also provide greater flexibility. With a Medigap plan, you can access any hospital or doctor in the country who accepts Medicare.
How to sign up for Medigap
Before signing up for Medigap, make sure to do your research. The cost of Medigap plans can vary by state. Resources to help you include:
— Trusted sites such as Medicare.gov and CMS.gov
— Licensed brokers or agents who offer Medigap plans
— Counselors with the State Health Insurance Assistance Program (SHIP)
— Medicare supplement websites, where you can search for plans by ZIP code
Once you’ve settled on a plan, you can fill out an application. Following approval, you should review the policy to make sure it’s still the right fit.
Note that you can enroll in a Medigap plan during the six-month window once you’ve turned 65 and enrolled in Medicare Part B. You can also sign up for Medigap after this period, but prices could be higher or your application could be denied due to major health issues you may have. Medigap plans also do not cover prescriptions, so you may need to work with an advisor to enroll in a separate Medicare Part D plan.
Medicare Savings Programs for Low-Income Seniors
Americans with very low incomes may be eligible for extra help with Medicare premiums and health care costs. The four primary Medicare Savings Programs are:
— The Qualified Medicare Beneficiary Program, which helps pay for premiums, deductibles, coinsurance, co-payments and prescription drugs. The monthly income limit for an individual in 2025 is $1,325, and the resource limit (for stocks, bonds or money in a checking, savings or retirement account) is $9,660. For a married couple, the monthly income limit is $1,783, and the resource limit is $14,470.
— The Specified Low-Income Medicare Beneficiary Program, which helps pay for Medicare Part B premiums and prescription drugs. The monthly income limit for an individual in 2025 is $1,585, and the resource limit is $9,660. A married couple’s income limit is $2,135, and the resource limit is $14,470.
— The Qualifying Individual Program, which helps pay for Medicare Part B premiums. The monthly income limit for an individual in 2025 is $1,781, and the resource limit is $9,660. A married couple’s monthly income limit is $2,400, and the resource limit is $14,470.
— The Qualified Disabled Working Individual Program, which helps to pay Part A premiums only for those who have a disability, are working and lost their $0 premium Part A coverage because they chose to return to work. The monthly income limit for an individual in 2025 is $5,302, and the resource limit is $4,000. For a married couple, the monthly income limit is $7,135, and the resource limit is $6,000.
Note that income limits are slightly higher in some states, such as Alaska and Hawaii. Make sure to review income and resources specific to your state.
Medicare Resources
The Medicare system is complex, and most people should seek help when choosing a plan. U.S. News’ Best Medicare Advantage Companies and Best Medicare Part D Companies can help you navigate the options and get the proper medical coverage. You can also get help via phone or in person from SHIP. Those agencies often maintain office hours at senior centers or other locations.
Omdahl stresses that seeking reliable information is essential because the onslaught of mailings and TV commercials can be overwhelming. Since January 1, 2023, the Centers for Medicare & Medicaid Services must approve Medicare Advantage plan commercials prior to airing — relieving some of the misinformation that causes confusion among beneficiaries. When in doubt, seek an expert for help.
More from U.S. News
PACE and Medicare: Eligibility, Coverage and Cost
What Is the “Welcome to Medicare” Preventive Visit?
What Is Medicare’s Chronic Care Management Program?
What Is Medicare: Coverage, Cost and Enrollment originally appeared on usnews.com
Update 05/15/25: This story was previously published at an earlier date and has been updated with new information.
