Original Medicare Explained: How Medicare Parts A and B Work
Published on July 2, 2026
If you’re new to Medicare, you’re not alone. Medicare can feel confusing at first because there are multiple parts, different enrollment periods, and important coverage decisions to make.
The good news is that Medicare starts with just two parts:
- Medicare Part A (Hospital Insurance)
- Medicare Part B (Medical Insurance)
Together, Parts A and B are called Original Medicare.
This guide explains what Original Medicare covers, what it costs, how to enroll, and the gaps you should understand before choosing additional coverage.
What Is Original Medicare?
Original Medicare
The Foundation of Your Medicare Coverage
Original Medicare is the federal health insurance program administered by the government. It includes Medicare Part A and Medicare Part B.
A
Medicare Part A
Hospital Coverage
Part A helps cover inpatient and facility-based care.
✓ Hospital stays
✓ Skilled nursing facility care
✓ Hospice care
✓ Some home health services
B
Medicare Part B
Medical Coverage
Part B helps cover doctor, outpatient, and preventive care.
✓ Doctor visits and specialists
✓ Outpatient surgery
✓ Lab work and X-rays
✓ Preventive services
✓ Durable medical equipment
Together, Medicare Part A and Part B form the foundation of your Medicare coverage.
The Biggest Advantage of Original Medicare
Biggest Advantage
Freedom to Choose Your Doctors
One of the biggest benefits of Original Medicare is access. You can see any provider, specialist, or hospital that accepts Medicare.
Any doctor
Who accepts Medicare
Any specialist
Who accepts Medicare
Any hospital
That accepts Medicare
—
Fewer Restrictions
You Do Not Need
Provider networks
No narrow HMO-style network to stay inside
Referrals
You usually do not need permission to see a specialist
Prior authorization for most services
Most Medicare-covered services do not require plan approval first
Key Takeaway
Original Medicare gives you one of the broadest health insurance networks available in the United States.
What Medicare Part A Covers
Medicare Part A
What Medicare Part A Covers
Medicare Part A is often called hospital insurance because it helps cover inpatient and facility-based care.
✓
Skilled nursing facility care
✓
Some home health services
Simple way to think about it: Part A mainly helps with hospital and facility-based care.
What Medicare Part B Covers
Medicare Part B
What Medicare Part B Covers
Medicare Part B helps cover outpatient medical care, including doctor visits, preventive services, outpatient care, and certain medical equipment.
✓
Doctor visits
Primary care doctors, specialists, and follow-up appointments
✓
Preventive services
Annual wellness visits, certain screenings, and many vaccinations
✓
Outpatient care
Physical therapy, diagnostic testing, and outpatient procedures
✓
Medical equipment
Walkers, wheelchairs, oxygen equipment, and other durable medical equipment
Simple way to think about it: Part B mainly helps with doctor, outpatient, preventive, and medical equipment costs.
What Does Original Medicare Cost?
Original Medicare Costs
What You May Pay with Original Medicare
Original Medicare helps pay for many medical services, but it does not mean all of your care is without cost.
A
Part A premium
Most people pay $0 for Medicare Part A because they worked and paid Medicare taxes for at least 10 years.
B
Part B premium
Most beneficiaries pay a monthly Part B premium. This premium can be higher for people with higher incomes.
$
Deductibles and cost sharing
Even after Medicare starts paying, you may still be responsible for deductibles, coinsurance, and copayments.
Simple way to think about it: Original Medicare helps pay for care, but it does not cover every cost. This is where many people discover Medicare’s biggest limitation.
The Biggest Shortcoming
Major Limitation
Original Medicare Has No Out-of-Pocket Maximum
Unlike many employer health plans, Original Medicare does not include a yearly cap on your medical expenses.
$
No built-in yearly spending limit
There is no limit to what you could potentially spend if you experience a serious illness, multiple hospitalizations, extensive outpatient treatment, or ongoing medical care.
20%
Part B cost sharing can continue adding up
If Medicare approves a service under Part B, Medicare generally pays about 80% of the approved amount, while you remain responsible for approximately 20%.
Why this matters: Many people are comfortable with Medicare covering 80% until they realize there is no maximum financial protection built into Original Medicare. This is one reason beneficiaries often add coverage to help limit exposure to large medical bills.
Do I Really Need Supplemental Insurance?
Supplemental Coverage
Do I Need Supplemental Insurance with Original Medicare?
Original Medicare gives you strong access to doctors and hospitals. Supplemental insurance is mainly about deciding whether you want help limiting the costs Medicare leaves behind.
The Main Question
Are you comfortable paying Medicare’s leftover costs yourself?
The question is not whether Original Medicare is good coverage. In many ways, it is. The real question is whether you want to be responsible for the deductibles, coinsurance, and other cost-sharing that can remain after Medicare pays its portion.
Predictability
Helps make medical bills easier to plan for
Protection
Helps reduce exposure to larger medical bills
Peace of Mind
Helps avoid wondering how high costs could climb
Risk Tolerance
Helps match your coverage to your budget and comfort level
Why This Matters in a Bigger Medical Year
A major health event can involve more than one type of bill.
For example, someone may have an emergency hospital stay, surgery, specialist visits, diagnostic testing, physical therapy, medical equipment, and follow-up appointments. Supplemental insurance can help reduce how much of that remaining cost-sharing falls directly on you.
Simple Illustration
The decision often comes down to how much risk you want to keep yourself.
Approved Charges
$10,000
Your share could be about $2,000.
Approved Charges
$50,000
Your share could be about $10,000.
Approved Charges
$100,000
Your share could be about $20,000.
These examples are simplified illustrations. Actual costs depend on the service, Medicare-approved amounts, deductibles, and how each claim is processed.
Simple way to think about it: You may not need supplemental insurance because Original Medicare is weak. You may want it because Original Medicare leaves some costs open-ended, especially in a year when you use a lot of care.
When and How Do You Enroll in Medicare?
Medicare Enrollment
Initial Enrollment Period
Most people first become eligible for Medicare at age 65. Your Initial Enrollment Period gives you a 7-month window to enroll.
Your 7-Month Window
3 Months Before + Birthday Month + 3 Months After
✓
If you’re already receiving Social Security
Many people are automatically enrolled in Medicare.
!
If you’re not receiving Social Security
You will generally need to enroll through Social Security.
Simple way to think about it: Your Initial Enrollment Period starts 3 months before your 65th birthday month and ends 3 months after it.
What Original Medicare Does NOT Include
Coverage Gaps
What Original Medicare Does NOT Include
Original Medicare covers many medical services, but it does not cover everything.
×
Most prescription drugs
×
Most long-term custodial care
A simple way to think about it: Original Medicare provides broad medical access, but many people add extra coverage because Original Medicare leaves important gaps.
What Most Medicare Beneficiaries Add
Additional Coverage
What Most Medicare Beneficiaries Add
After enrolling in Original Medicare, many people choose additional coverage to help fill Medicare’s gaps.
M
Medicare Supplement (Medigap)
Helps pay many of Medicare’s deductibles, copayments, and coinsurance.
D
Medicare Part D
Provides prescription drug coverage.
C
Medicare Advantage (Part C)
An alternative way to receive Medicare benefits through a private insurance company.
Simple way to think about it: Original Medicare is the foundation, but many people add coverage for prescriptions, out-of-pocket costs, or an alternative Medicare plan structure.
Bottom Line
Original Medicare Parts A and B provide excellent access to doctors and hospitals across the country and serve as the foundation of Medicare coverage.
However, Original Medicare also has important gaps, including:
- No prescription drug coverage
- No routine dental, vision, or hearing coverage
- No out-of-pocket maximum
Understanding these strengths and limitations is the first step toward building a Medicare plan that fits your needs and budget.
