Medicare Part A is hospital insurance, and Part B is medical insurance. Together, they form what’s called “Original Medicare,” the federal health coverage available to Americans 65 and older. Part A covers care you receive as an inpatient, while Part B covers outpatient services, doctor visits, and preventive care. Most people need both parts working together to have meaningful coverage.
What Part A Covers
Part A is the hospital side of Medicare. It helps pay for inpatient care in hospitals, critical access hospitals, and skilled nursing facilities. It also covers hospice care and some home health care services. The key word is “inpatient.” If you’re formally admitted to a hospital and staying overnight (or longer), Part A is what kicks in.
Skilled nursing facility coverage applies when you need short-term rehabilitative care after a hospital stay, not long-term custodial care. This is a common point of confusion. If you need help with daily activities like bathing or eating on an ongoing basis, that’s considered long-term care, and Medicare does not cover it.
What Part B Covers
Part B handles two broad categories: medically necessary services and preventive services. Medically necessary services include anything that meets accepted standards of medical practice to diagnose or treat a condition. Preventive services are designed to catch illness early or prevent it altogether, like flu shots and cancer screenings.
Beyond regular doctor visits, Part B covers ambulance services, durable medical equipment (wheelchairs, walkers, oxygen equipment), mental health and substance use disorder treatment, clinical research participation, and a limited set of outpatient prescription drugs. Most prescription drugs fall under a separate Part D plan, but Part B picks up certain medications administered in a doctor’s office or clinic.
What Original Medicare Does Not Cover
Even with both Part A and Part B, there are significant gaps. Original Medicare does not cover:
- Routine dental care, including cleanings, fillings, tooth extractions, and dentures
- Vision care, including eye exams for prescription glasses
- Hearing aids and the exams needed to fit them
- Long-term care in a nursing home or assisted living facility
- Cosmetic surgery
- Routine physical exams (though Medicare does cover an annual “wellness visit,” which is slightly different)
These exclusions are a big reason many people add supplemental coverage through a Medigap policy or choose a Medicare Advantage plan (Part C), which bundles Parts A and B together and often includes dental, vision, and hearing benefits.
What Part A Costs in 2025
Most people pay nothing for Part A. If you or your spouse paid Medicare taxes for at least 10 years (40 quarters), your Part A premium is $0. You’ve already paid for it through payroll taxes during your working life.
If you don’t qualify for premium-free Part A, the costs can be steep. People with 7.5 to 10 years of work history pay a reduced premium of $285 per month in 2025. Those with fewer than 7.5 years of qualifying work pay the full premium: $518 per month.
Regardless of whether you pay a premium, Part A has a deductible. In 2025, the inpatient hospital deductible is $1,676 per benefit period. A benefit period starts when you’re admitted and ends once you’ve been out of the hospital or skilled nursing facility for 60 consecutive days. If you’re hospitalized twice within that window, you pay the deductible once. If you’re hospitalized again after 60 days, you pay it again.
What Part B Costs in 2025
Part B is not free. Everyone enrolled pays a monthly premium, and unlike Part A, there’s no way to earn premium-free coverage. The standard Part B premium in 2025 is based on your income. Most people pay the base amount, but higher earners pay more through an income-related monthly adjustment. This surcharge, known as IRMAA, is calculated using your tax return from two years prior. For example, 2025 premiums are based on your 2023 income.
Single filers earning more than $109,000 and married couples filing jointly above $218,000 start paying higher premiums. The increases are tiered, and at the highest income levels, premiums can reach several hundred dollars per month. Part B also has an annual deductible you must meet before coverage begins paying its share. After the deductible, you typically pay 20% of the Medicare-approved amount for most services.
Who Qualifies for Medicare
The standard eligibility age is 65. You can also qualify earlier if you have a disability and have been receiving Social Security disability benefits for 24 months, if you have end-stage renal disease (permanent kidney failure requiring dialysis or a transplant), or if you have ALS (Lou Gehrig’s disease). People with ALS qualify for Medicare as soon as their disability benefits begin, without the usual 24-month waiting period.
When and How to Enroll
Your Initial Enrollment Period is a seven-month window centered on your 65th birthday. It starts three months before the month you turn 65 and ends three months after that birthday month. Signing up during the first three months gives you the earliest possible coverage start date. Waiting until the tail end of the window can delay when your coverage begins.
If you’re already receiving Social Security benefits when you turn 65, you’ll be enrolled in Parts A and B automatically. If you’re not collecting Social Security yet, you need to sign up yourself through the Social Security Administration.
Late Enrollment Penalties
Missing your enrollment window for Part B carries a financial penalty that lasts as long as you have Medicare. Your Part B premium increases by 10% for every full 12-month period you were eligible but didn’t sign up. So if you delayed enrollment by two years, you’d pay a 20% surcharge on top of your standard premium for the rest of your time on Medicare.
There is an important exception. If you delayed Part B because you had health coverage through your own employer (or your spouse’s employer), you qualify for a Special Enrollment Period that lets you sign up penalty-free when that job-based coverage ends. This exception applies to active employment coverage only. COBRA and retiree health plans do not count.
Parts vs. Plans
One source of confusion is the difference between Medicare “parts” and Medicare “plans.” The parts (A, B, C, D) are the building blocks of Medicare itself. Part A is hospital insurance. Part B is medical insurance. Part C (Medicare Advantage) is a private-sector alternative that combines A and B, often with extras. Part D is prescription drug coverage.
A “plan,” on the other hand, refers to the specific product you choose within a part. You might pick a particular Medicare Advantage plan from one insurer or a Part D drug plan from another. Medigap (Medicare Supplement) policies are separate insurance plans designed to fill the cost-sharing gaps in Original Medicare, covering things like that 20% coinsurance on Part B services or the Part A hospital deductible. You can only buy Medigap if you’re enrolled in Original Medicare (Parts A and B), not if you’re on a Medicare Advantage plan.