What Is Medicare? Parts A, B, C & D Explained (2026)

Medicare comes in four parts, A, B, C, and D, and how you combine them decides what you pay and which doctors you can see. It's the federal health insurance program for people age 65 and older, plus some younger people with disabilities or specific conditions. This guide explains what each part covers, who qualifies, what it costs in 2026, when to sign up, and what Medicare does not pay for, so you can make the first decisions with confidence.

In this guide

Medicare runs on a few core choices, and the order they come in matters. You confirm you're eligible, decide between the two ways to receive benefits, sign up during the right window, and then handle the gaps Medicare leaves open. The sections below walk that path.

Who qualifies for Medicare

Medicare eligibility runs on age first, then on a few disability and medical paths for younger people.

You qualify at age 65 if you're entitled to, or eligible for, monthly Social Security benefits, and most people at 65 also get premium-free Part A because they or a spouse paid Medicare taxes for at least 40 quarters (about 10 years). "A spouse" is broader than it sounds: a current, former, or late spouse's record can carry you, subject to Social Security's own rules, such as how long the marriage lasted and whether you've remarried.6,1

If you're short of 40 quarters, don't stop reading there. Forty quarters is one sufficient route to insured status rather than a hard floor, and fewer can be enough when a period of disability interrupted your working years, so have Social Security check your record. If you genuinely don't qualify, you can still buy Part A at the premiums in the table below. The buy-in is the one place a residency test applies: to buy Part A you must be 65, enrolled in Part B, and either a U.S. citizen or a lawful permanent resident who has lived in the country continuously for the five years before you apply. Premium-free Part A carries no five-year residency test at all.6

The Centers for Medicare and Medicaid Services lists several ways to get Medicare before 65; the three main ones are:

• Disability. After you've received Social Security Disability Insurance (SSDI) for 24 months, you're enrolled automatically in Parts A and B; coverage starts in the 25th month. The same 24-month clock counts disability benefits drawn on a parent's or a late spouse's record, not only SSDI on your own.6,7
• ALS. A diagnosis of amyotrophic lateral sclerosis (Lou Gehrig's disease) waives the 24-month wait. Medicare starts the same month your SSDI benefits begin.6
• End-stage renal disease (ESRD). Permanent kidney failure requiring dialysis or a transplant can qualify you at any age. Any age removes the age bar, not the work-record bar: you must have worked long enough under Social Security, the Railroad Retirement Board, or as a government employee, or already be getting or be eligible for Social Security or Railroad Retirement benefits, or be the spouse or dependent child of someone who meets one of those. If ESRD is your only basis for Medicare, coverage usually starts in the fourth month of dialysis.6

The four parts of Medicare

The most useful thing to understand is what each part does. The official breakdown lives on the parts of Medicare page; here is the working version.

Part A is hospital insurance. It covers inpatient hospital stays, hospice, some home health care, and short-term skilled nursing facility care when you meet all of Medicare's conditions, which include a qualifying inpatient hospital stay of at least three days in a row.8 Most people pay no premium for Part A. You do pay a deductible each benefit period before it starts covering an inpatient stay.1

Part B is medical insurance. It covers doctors' services, outpatient care, durable medical equipment, mental health services, and many preventive services.9 Part B has a monthly premium and an annual deductible, after which you generally pay 20% of the Medicare-approved amount for most services.1

Part C is Medicare Advantage. This is not a separate benefit so much as a different way to receive Parts A and B. Private plans approved by Medicare bundle your hospital and medical coverage, usually add drug coverage, and often include extras like routine dental or vision. In exchange, you follow the plan's rules on provider networks and prior authorization, which the next section sets out.10

Part D is prescription drug coverage. Private plans cover outpatient prescription drugs. You can add a standalone Part D plan to Original Medicare, or get drug coverage built into a Medicare Advantage plan.

The two ways to get Medicare

Every beneficiary picks one of two structures. This is the decision that shapes your costs, your provider access, and your paperwork for the year.

Original Medicare is the federal program directly. You get Parts A and B, and in most cases you don't need the advance approval (prior authorization) that private plans can require before a service is covered. Original Medicare has no annual out-of-pocket limit of its own, and the remedy CMS names in the same breath is supplemental coverage rather than a cap, so many people add two things: a standalone Part D drug plan, and a Medigap (Medicare Supplement) policy that can help pay the deductibles and coinsurance Original Medicare leaves to you. Medicaid, or employer, retiree, or union coverage, can play that same role.10,11

Medicare Advantage replaces that bundle with a single private plan. It must cover all the medically necessary services Parts A and B cover except hospice care, which Original Medicare keeps covering even after you join, along with some clinical-trial costs. It usually folds in Part D as well, and it caps your in-network out-of-pocket spending. In 2026 that cap is federally limited to $9,250 for in-network services, and many plans set it lower. The tradeoff: you're generally limited to the plan's network, though emergency care, out-of-area urgent care, and temporary out-of-area dialysis are covered whether you get them in network or out, and the plan may require prior authorization before it covers certain services. You can't use a Medigap policy to pay a Medicare Advantage plan's costs, but that isn't a permanent lock-out: join Advantage for the first time, find it doesn't suit you, and federal law gives you a trial right to buy a Medigap policy and a separate drug plan if you return to Original Medicare within 12 months of joining. Past that window the door mostly closes, and someone who dropped a Medigap policy to try Advantage may not get it, or any policy, back.10 Which plans you can actually choose from depends on where you live; our guide to Medicare plans and coverage by state shows how it varies.

One point that surprises people: with either path, you almost always still pay the Part B premium. Medicare Advantage doesn't replace Part B; it's an additional way to receive those benefits, so the Part B premium normally continues alongside any plan premium.10 The exception is worth knowing before you compare plans: CMS says some Advantage plans "may have a $0 premium and may help pay all or part of your Part B premium," so some plans reduce, and occasionally cover, the Part B premium you would otherwise pay in full.10

What Medicare costs in 2026

The Centers for Medicare and Medicaid Services announced the 2026 figures on November 14, 2025. They apply from January 1 through December 31, 2026.1

A benefit period is the unit Part A uses. It begins the day you're admitted as an inpatient and ends after you've gone 60 days in a row without inpatient hospital care or skilled care in a skilled nursing facility. Because a new benefit period can start later in the same year, the Part A deductible can apply more than once in twelve months.1

Higher earners pay an income-related surcharge on top of the standard Part B premium and whatever Part D plan premium you pay, called IRMAA. It's based on the modified adjusted gross income on your tax return from two years earlier, or from three years earlier when that return isn't available. In 2026 the surcharge starts above $109,000 for a single filer (or $218,000 for a couple) and rises through five tiers; at the top tier the total Part B premium reaches $689.90 a month. If you file married-but-separately and lived with your spouse at any point in the year, a compressed three-row scale applies instead, and Social Security assumes that's your situation unless you tell it you lived apart for the whole year. Treat those totals as the premium before other adjustments rather than the final bill: a Part B or Part D late-enrollment penalty is added on top, and a Medicare Advantage plan's Part B give-back is subtracted from it.12

When to sign up

Timing is where Medicare costs people real money, because some late penalties stay on your premium for as long as you have that coverage.3

Your Initial Enrollment Period is a seven-month window around your 65th birthday: the three months before the month you turn 65, that month, and the three months after. If you start getting Social Security or Railroad Retirement Board benefits at least four months before you turn 65, you're enrolled in Parts A and B automatically, unless you live in Puerto Rico or outside the United States, where only Part A is automatic. Otherwise you sign up yourself through the Social Security Administration.2

If you miss that window and no exception applies, the late penalties are steep and ongoing:

• Part B: unless you qualify for a Special Enrollment Period or a Medicare Savings Program, your premium rises 10% for each full 12-month period you could have had Part B but didn't, and the penalty lasts as long as you have Part B.3
• Part D: if you don't join a drug plan when you first get Medicare, or you later go 63 days or more without creditable drug coverage, 1% of the national base premium is added for each full month you went without it, for as long as you have Part D. There is generally no Part D penalty if you had creditable drug coverage or you qualify for Extra Help.3

There's an important exception, with a deadline inside it. If you're still working at 65 and have coverage through a current employer (yours, your spouse's, or a family member's if you have a disability), you can usually delay Part B without penalty and sign up later through a Special Enrollment Period. That window is not open-ended: it runs from the month after your Initial Enrollment Period ends until eight months after the employment or the group health coverage ends, whichever happens first. It's also narrower than most people assume. Medicare doesn't treat COBRA, retiree coverage, or Marketplace coverage as job-based coverage here, so when one of those ends it opens no Part B Special Enrollment Period.2 Part D runs on its own clock: there's generally no penalty while you have creditable drug coverage, but going 63 days or more without it starts one.3

And if you missed your window with no exception to fall back on, you aren't locked out for good. The General Enrollment Period runs January 1 through March 31 every year, and coverage starts the month after you sign up, though you might still owe a late enrollment penalty.2

What Medicare doesn't cover

Knowing the gaps matters as much as knowing the coverage, because the gaps are where families get surprised.

The largest gap is long-term custodial care. Medicare pays for skilled nursing only on a short-term, post-acute basis: up to 100 days per benefit period, and generally only after a qualifying three-day inpatient hospital stay, per the skilled nursing facility benefit. Time spent under observation or in the emergency room before you're formally admitted doesn't count toward those three days, even overnight. Medicare does not pay for ongoing help with daily activities, the kind of care most people mean by "nursing home." For that, families rely on private pay, long-term care insurance, or Medicaid.4

The three-day requirement is not a dead end, and this is where families give up too early. Your doctor's Accountable Care Organization may hold a waiver of it, and a Medicare Advantage plan may waive it too. If you re-enter a facility within 30 days of leaving one, you don't need a new three-day stay at all. If a hospital switched you from inpatient to "outpatient getting observation services" during your stay, that switch carries its own appeal right, and the date decides which track you're on: a change on or after February 14, 2025 goes to the fast appeal, which stays open and survives your discharge, and which the January 2026 cutoff doesn't touch, while an older stay, back to January 2009 but no later than February 13, 2025, had to be appealed by January 2, 2026 and is now denied unless you give a good-cause reason for filing late, such as serious illness or having been given the wrong instructions. Our guide to observation status walks through both. And if none of those fit, Medicare's own advice is to ask about other settings, like home health, and other payers, like Medicaid or veterans' benefits, rather than assuming the answer is no.4,1

Original Medicare also doesn't cover routine dental, vision, and hearing care, apart from narrow medically necessary exceptions.5 It usually doesn't cover care you get while traveling outside the United States either.13 Many Medicare Advantage plans add some dental, vision, or hearing benefits, which is part of their appeal, but not every plan does, so check what a specific plan covers.10,5

Help paying for Medicare

Several programs lower Medicare's costs for people with limited income and resources. Check each one before you assume your income or savings are too high.

• Medicare Savings Programs are run by state Medicaid agencies and can pay your Part B premium, and in some cases your deductibles and coinsurance. In 2026 the federal resource limits are $9,950 for an individual and $14,910 for a couple, but those are not an absolute cutoff: states can disregard certain income and resources, and some have dropped the resource test entirely, so apply rather than rule yourself out.14 Because they're run state by state, the names and details differ, which our guide to Medicare Savings Programs by state breaks down.
• Extra Help (the Part D Low-Income Subsidy) helps pay Part D premiums, deductibles, and copays, though it covers the premium only up to a regional benchmark amount.15 Its resource limits are higher than the Medicare Savings Program limits, so savings too high for a Medicare Savings Program may still fit under the limit for the drug-cost help program.1 Enrolling in QMB, SLMB, or QI qualifies you for Extra Help automatically, so those aren't two separate errands.14
• Medigap (Medicare Supplement Insurance) works differently: it's a policy you buy from an insurance company, and it's one of the kinds of supplemental coverage CMS names for Original Medicare, which otherwise has no yearly limit on what you pay out of pocket.10 Your strongest opportunity to buy one is the one-time, six-month Medigap Open Enrollment Period that starts the first month you're both 65 and enrolled in Part B; during it, an insurer can't refuse to sell you a policy it offers, use medical underwriting on your application, or charge you more because of your health. One limit survives that window: an insurer may still refuse to cover your out-of-pocket costs for a pre-existing condition for up to six months, and it can't impose even that if you had at least six months of continuous prior creditable coverage.11

If you have both Medicare and Medicaid, the two programs coordinate, and special plans exist to integrate them. See the dual-eligible guide below.

Learn More

Choosing your coverage

Signing up and timing

Costs and help paying

What Medicare covers

Protecting yourself

Find personalized help comparing your Medicare options and enrollment windows at brevy.com.

The information on Brevy.com is for educational purposes only and is not a substitute for professional legal, financial, or medical advice. Rules vary by state and program and change frequently. Always verify with the relevant agency or a qualified professional. Brevy is not a law firm, financial advisor, or healthcare provider.