Your Policy Path Editorial Team

Licensed Insurance Professionals

Updated 2026-05-06Fact-Checked

Medicare Explained: A Complete Guide to Parts A, B, C, and D

By Your Policy Path Editorial Team•19 min read•Updated 2026-05-06

What Is Medicare?
Who Is Eligible for Medicare?
Medicare Part A: Hospital Insurance
Medicare Part B: Medical Insurance
Medicare Part C: Medicare Advantage
Medicare Part D: Prescription Drug Coverage
Medigap (Medicare Supplement Insurance)
Medicare Enrollment Periods
Medicare Costs and Premiums in 2026
Late Enrollment Penalties
What Medicare Does NOT Cover
Original Medicare vs Medicare Advantage
How to Enroll in Medicare
FAQ

What Is Medicare?

Medicare is the federal health insurance program for Americans aged 65 and older, as well as certain younger people with disabilities or specific medical conditions. Established in 1965, Medicare now covers over 67 million Americans and is one of the largest health insurance programs in the world.

Medicare is administered by the Centers for Medicare & Medicaid Services (CMS), a part of the U.S. Department of Health and Human Services. It's funded through a combination of payroll taxes, beneficiary premiums, and general federal revenue.

Understanding Medicare can feel overwhelming — it's divided into multiple parts, each covering different services, with different costs and enrollment rules. But once you break it down piece by piece, it becomes much more manageable.

Here's the quick overview:

Part A — Hospital insurance (inpatient care)
Part B — Medical insurance (outpatient care and doctor visits)
Part C — Medicare Advantage (private plan alternative that bundles A + B, often with extras)
Part D — Prescription drug coverage

Parts A and B together are called "Original Medicare." Part C is an alternative way to receive your Medicare benefits through private insurers. Part D is add-on prescription drug coverage available with Original Medicare or sometimes bundled into Part C plans.

Who Is Eligible for Medicare?

Age-Based Eligibility

You're eligible for Medicare when you turn 65 if you're a U.S. citizen or permanent legal resident who has lived in the United States for at least 5 consecutive years. You don't need to be retired — you can enroll at 65 even if you're still working.

Work History Requirements

Most people qualify for premium-free Part A (hospital insurance) if they or their spouse paid Medicare payroll taxes for at least 40 quarters (10 years). If you don't meet this requirement, you can still enroll in Part A but will pay a monthly premium.

Part B is available to all Medicare-eligible individuals regardless of work history, but everyone pays a monthly premium.

Under-65 Eligibility

You can qualify for Medicare before age 65 if you:

Have received Social Security Disability Insurance (SSDI) for 24 months. Medicare begins automatically in your 25th month of SSDI benefits.
Have End-Stage Renal Disease (ESRD). If you need regular dialysis or a kidney transplant, you may qualify for Medicare regardless of age.
Have Amyotrophic Lateral Sclerosis (ALS/Lou Gehrig's disease). Medicare begins the same month your SSDI benefits start — no 24-month waiting period.

Medicare Part A: Hospital Insurance

Part A covers inpatient hospital care and related services. Think of it as coverage for when you're admitted to a facility.

What Part A Covers

Inpatient hospital stays. Room, meals, nursing care, medications administered during your stay, lab tests, and operating room costs
Skilled nursing facility (SNF) care. Up to 100 days per benefit period following a qualifying hospital stay of at least 3 days
Home health care. Part-time skilled nursing care, physical therapy, occupational therapy, and speech therapy in your home (if medically necessary)
Hospice care. Comfort care for terminally ill patients with a life expectancy of 6 months or less, including medication for symptom management, counseling, and respite care
Inpatient psychiatric care. Up to 190 days lifetime in a psychiatric hospital

Part A Costs (2026)

Premium: $0 for most people (if you or your spouse paid Medicare taxes for 40+ quarters). Up to $518/month if you don't qualify for premium-free Part A.
Deductible: $1,676 per benefit period (each time you're admitted to the hospital after being out for 60+ days, a new benefit period begins)
Hospital coinsurance:
Days 1–60: $0 (after deductible)
Days 61–90: $419/day
Days 91–150 (lifetime reserve days): $838/day
Beyond 150 days: You pay 100%
Skilled nursing facility coinsurance:
Days 1–20: $0
Days 21–100: $209.50/day
Beyond 100 days: You pay 100%

Important Part A Details

A "benefit period" starts the day you're admitted to a hospital and ends when you've been out of the hospital or skilled nursing facility for 60 consecutive days. If you're readmitted after 60 days, a new benefit period begins and you pay the deductible again. There's no limit on the number of benefit periods.

Medicare Part B: Medical Insurance

Part B covers outpatient medical services — the care you receive outside of a hospital admission.

What Part B Covers

Doctor visits — both primary care and specialists
Outpatient procedures — same-day surgery, diagnostic tests
Preventive services — annual wellness visits, flu shots, mammograms, colonoscopies, diabetes screenings (many with no copay)
Lab tests and X-rays
Mental health services — outpatient therapy and psychiatry
Durable medical equipment (DME) — wheelchairs, walkers, hospital beds, oxygen equipment
Ambulance services (when medically necessary)
Physical and occupational therapy
Clinical research studies
Some home health care (not covered under Part A)
Second surgical opinions

Part B Costs (2026)

Premium: $185/month (standard). Higher-income beneficiaries pay more through Income-Related Monthly Adjustment Amount (IRMAA):
Individual income $106,000–$133,000: $259.40/month
$133,000–$167,000: $370.60/month
$167,000–$200,000: $481.80/month
$200,000–$500,000: $593.00/month
Above $500,000: $628.90/month
Annual deductible: $257
Coinsurance: You typically pay 20% of the Medicare-approved amount after the deductible, with no out-of-pocket maximum

The 20% Problem

One of the biggest gaps in Original Medicare is the Part B coinsurance. You pay 20% of the Medicare-approved amount for most services — and there is no annual out-of-pocket maximum. If you have a $200,000 surgery, you could owe $40,000. This unlimited cost exposure is the primary reason many beneficiaries purchase Medigap supplemental insurance or choose Medicare Advantage plans, which do have out-of-pocket maximums.

Medicare Part C: Medicare Advantage

Medicare Advantage (Part C) is an alternative way to receive your Medicare benefits. Instead of getting coverage directly from the federal government (Original Medicare), you enroll in a plan offered by a private insurance company that contracts with Medicare.

How Medicare Advantage Works

Medicare Advantage plans must cover everything that Original Medicare (Parts A and B) covers, but they can also offer additional benefits that Original Medicare doesn't — such as dental, vision, hearing, fitness programs, and over-the-counter drug allowances.

Most Medicare Advantage plans also include Part D prescription drug coverage, creating an all-in-one plan.

You still pay your Part B premium to Medicare. Many Medicare Advantage plans charge an additional monthly premium, though some have $0 premiums.

Types of Medicare Advantage Plans

HMO (Health Maintenance Organization): Requires you to use in-network providers and get referrals to see specialists. Lowest premiums but least flexibility.
PPO (Preferred Provider Organization): Allows you to see out-of-network providers at a higher cost. No referral required for specialists.
PFFS (Private Fee-for-Service): Determines how much it will pay providers and how much you pay. Can use any Medicare-accepting provider.
SNP (Special Needs Plans): Designed for people with specific diseases, limited income, or who live in certain institutions.
MSA (Medical Savings Account): High-deductible plan paired with a medical savings account that Medicare deposits money into.

Medicare Advantage Pros and Cons

Pros:

Out-of-pocket maximum (caps your annual costs — typically $3,000–$8,000)
Extra benefits (dental, vision, hearing, fitness)
Often includes Part D drug coverage
Some plans have $0 premiums
Simplified — one card, one plan

Cons:

Network restrictions (HMO plans limit provider choice)
Prior authorization requirements for some procedures
Not accepted everywhere — especially problematic when traveling
Plan benefits change annually
Cannot use Medigap with Medicare Advantage
Plans vary significantly by location

Who Should Consider Medicare Advantage

Medicare Advantage works well if you:

Live in an area with strong plan options and provider networks
Want dental, vision, and hearing coverage included
Prefer a single plan with an out-of-pocket cap
Want $0 or low-premium coverage
Don't travel frequently or spend extended time outside your plan's service area

Medicare Part D: Prescription Drug Coverage

Part D provides outpatient prescription drug coverage. It's offered through private insurance companies that contract with Medicare.

How Part D Works

Part D plans have a formulary — a list of covered drugs organized into tiers. Lower tiers (generics) have lower copays; higher tiers (brand-name, specialty) have higher copays.

Part D Cost Structure (2026)

Monthly premium: Varies by plan (national average approximately $40–$55/month). Higher-income beneficiaries pay IRMAA surcharges.
Annual deductible: Up to $590 (some plans have lower or $0 deductibles)
Copays/coinsurance: Varies by drug tier — generics may be $0–$15; preferred brands $20–$50; specialty drugs percentage-based

The Coverage Gap ("Donut Hole")

The Medicare Part D donut hole has been largely closed as of 2025 under the Inflation Reduction Act. Beneficiaries now pay no more than $2,000 in total out-of-pocket drug costs per year. Once you reach this threshold, you enter catastrophic coverage where you pay $0 for covered drugs for the rest of the year.

This is a major improvement from previous years when beneficiaries faced significant costs in the coverage gap.

How to Choose a Part D Plan

Make a list of all your current medications (including dosages)
Use the Medicare Plan Finder at Medicare.gov to compare plans in your area
Check that your medications are on the plan's formulary
Verify your preferred pharmacy is in the plan's network
Compare total annual costs (premiums + deductibles + copays), not just monthly premiums

Medigap (Medicare Supplement Insurance)

Medigap policies are sold by private insurance companies to help cover costs that Original Medicare doesn't — primarily deductibles, coinsurance, and copayments.

How Medigap Works

Medigap works alongside Original Medicare. Medicare pays its share first, then your Medigap policy pays some or all of the remaining costs. Medigap policies are standardized — each plan type (identified by a letter: A, B, C, D, F, G, K, L, M, N) offers specific benefits defined by the federal government.

Important: You can only use Medigap with Original Medicare. If you're enrolled in Medicare Advantage (Part C), you cannot purchase or use a Medigap policy.

Medigap Enrollment

The best time to buy Medigap is during your 6-month Medigap Open Enrollment Period, which begins the month you turn 65 AND are enrolled in Part B. During this period, insurance companies must sell you a Medigap policy at the standard rate regardless of your health — they cannot charge more or deny coverage based on pre-existing conditions.

After this window closes, insurers can use medical underwriting and may deny coverage or charge higher rates based on your health status.

Medicare Enrollment Periods

Understanding enrollment periods is critical to avoiding gaps in coverage and late enrollment penalties.

Initial Enrollment Period (IEP)

Your IEP is a 7-month window surrounding your 65th birthday:

3 months before your birth month
Your birth month
3 months after your birth month

This is when you should sign up for Parts A and B. If you're already receiving Social Security benefits, you'll be enrolled automatically.

General Enrollment Period (GEP)

If you missed your IEP, you can sign up during the GEP, which runs from January 1 through March 31 each year. Coverage begins July 1. You may face a late enrollment penalty.

Special Enrollment Period (SEP)

If you delayed enrollment because you had employer-sponsored health coverage (from your own job or your spouse's), you qualify for a SEP:

8-month period starting the month your employment or employer coverage ends (whichever comes first)
No late enrollment penalty applies

This is one of the most important rules in Medicare. If you have creditable employer coverage, you can delay Part B without penalty. But if you don't have creditable coverage and delay, penalties apply.

Annual Enrollment Period (AEP) / Open Enrollment

Running from October 15 through December 7 each year, the AEP is when you can:

Switch from Original Medicare to Medicare Advantage (or vice versa)
Switch between Medicare Advantage plans
Join, drop, or switch Part D plans

Changes take effect January 1 of the following year.

Medicare Advantage Open Enrollment Period

From January 1 through March 31, beneficiaries currently enrolled in a Medicare Advantage plan can:

Switch to a different Medicare Advantage plan
Drop Medicare Advantage and return to Original Medicare (and join a Part D plan)

Medicare Costs and Premiums in 2026

Here's a summary of what Medicare costs in 2026:

Part A:

Premium: $0 for most (up to $518/month without sufficient work history)
Deductible: $1,676 per benefit period
No annual out-of-pocket maximum

Part B:

Standard premium: $185/month (higher with IRMAA)
Annual deductible: $257
20% coinsurance, no annual out-of-pocket maximum

Part C (Medicare Advantage):

Varies by plan ($0 to $200+/month, in addition to Part B premium)
Annual out-of-pocket maximum: typically $3,000–$8,000

Part D:

Average premium: $40–$55/month
Maximum annual deductible: $590
Maximum annual out-of-pocket: $2,000

Medigap:

Varies by plan and location
Plan G: typically $100–$300/month
Plan N: typically $80–$250/month

Late Enrollment Penalties

Missing your enrollment deadlines can result in permanent penalties that increase your premiums for as long as you have Medicare.

Part A Late Enrollment Penalty

If you don't qualify for premium-free Part A and don't enroll when first eligible, your Part A premium may increase by 10%. You'll pay this higher premium for twice the number of years you delayed enrollment.

Part B Late Enrollment Penalty

This is the penalty most people need to worry about. For every 12-month period you could have had Part B but didn't sign up, your monthly premium increases by 10% — permanently.

Example: If you delay Part B for 3 years without creditable employer coverage, your Part B premium increases by 30% for the rest of your life. On a $185/month premium, that's an extra $55.50/month — $666 per year — forever.

Part D Late Enrollment Penalty

If you go 63 days or more without Part D or creditable prescription drug coverage, you'll pay a penalty of 1% of the national base beneficiary premium per month for every month you delayed. This penalty is added to your Part D premium permanently.

Example: If you delay Part D for 24 months, your penalty is 24% × $36.78 (2026 base premium) = approximately $8.83/month added to your Part D premium permanently.

How to Avoid Penalties

Enroll during your Initial Enrollment Period
If you have employer coverage, document it and enroll within 8 months of losing it
Don't assume your employer coverage is "creditable" — verify with your employer or insurer
When in doubt, enroll on time. The penalties are permanent.

What Medicare Does NOT Cover

Despite its broad coverage, Medicare has significant gaps:

Long-term care / custodial care. Medicare does NOT cover nursing home stays for custodial care (help with daily activities like bathing, dressing, eating). It only covers skilled nursing care for up to 100 days following a qualifying hospital stay.
Dental care. Routine dental (cleanings, fillings, dentures, extractions) is generally not covered by Original Medicare. Some Medicare Advantage plans include dental.
Vision care. Routine eye exams and eyeglasses are not covered. Medicare does cover eye exams for specific conditions (glaucoma, diabetic eye disease) and cataract surgery.
Hearing aids. Not covered by Original Medicare. Some Medicare Advantage plans include hearing aid benefits.
Overseas healthcare. Medicare generally does not cover healthcare outside the United States (some Medigap plans offer limited foreign travel emergency coverage).
Cosmetic surgery. Not covered.
Acupuncture (except for chronic low back pain with certain restrictions).
Concierge/boutique physician fees.

Understanding these gaps is essential for planning your complete healthcare coverage in retirement. Many beneficiaries address these gaps through Medicare Advantage plans (which often include dental, vision, and hearing), standalone dental/vision insurance, or long-term care insurance.

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Original Medicare vs Medicare Advantage

This is the biggest decision most new Medicare beneficiaries face. Here's how to think about it:

Choose Original Medicare + Medigap + Part D if you:

Want maximum provider flexibility (any doctor/hospital that accepts Medicare)
Travel frequently or live in multiple states
Can afford the Medigap premium
Want predictable, low out-of-pocket costs
Don't need dental/vision/hearing through your insurance

Choose Medicare Advantage if you:

Want an all-in-one plan with lower premiums
Are comfortable using in-network providers
Want dental, vision, and hearing coverage included
Live in an area with strong Medicare Advantage plan options
Are willing to deal with prior authorization requirements

Neither option is universally better — it depends on your health, location, budget, and preferences.

How to Enroll in Medicare

Step 1: Determine your eligibility date. If you're approaching 65 and already receiving Social Security, you'll be automatically enrolled in Parts A and B.

Step 2: If you're not automatically enrolled, sign up during your IEP at ssa.gov or your local Social Security office. You can also call Social Security at 1-800-772-1213.

Step 3: Decide between Original Medicare and Medicare Advantage. Use the Medicare Plan Finder at medicare.gov to compare options in your area.

Step 4: If choosing Original Medicare, consider adding a Medigap policy and a standalone Part D plan. Shop during your Medigap Open Enrollment Period for guaranteed acceptance.

Step 5: If choosing Medicare Advantage, compare plans carefully — check provider networks, drug formularies, extra benefits, and out-of-pocket maximums.

Step 6: Mark your calendar for future enrollment periods so you can make changes if your needs evolve.

Frequently Asked Questions

When should I sign up for Medicare?

Sign up during your Initial Enrollment Period — the 7-month window that starts 3 months before your 65th birthday month and ends 3 months after. If you're still working with employer health coverage, you may be able to delay Part B without penalty — but verify that your employer plan qualifies as creditable coverage. The safest approach is to enroll at 65 unless you have confirmed creditable employer coverage.

Is Medicare free?

Part A is free for most people who (or whose spouse) paid Medicare taxes for at least 10 years. Part B is not free — the standard premium is $185/month in 2026, with higher premiums for higher-income beneficiaries. Part D and Medicare Advantage plans also have premiums. You'll also pay deductibles, coinsurance, and copays when you receive care. Medicare covers a lot, but it's not free.

What's the difference between Medicare and Medicaid?

Medicare is federal health insurance based on age (65+) or disability — available regardless of income. Medicaid is a joint federal-state program that provides health coverage to people with limited income and resources. Some people qualify for both ("dual eligibles") and receive coverage from both programs. Medicaid also covers long-term nursing home care, which Medicare generally does not.

Do I need Medicare if I have employer insurance?

If you're still working and have employer health coverage, you may not need to enroll in Part B immediately. If your employer has 20+ employees, your employer plan is primary and Medicare is secondary. You can delay Part B without penalty and enroll when you leave the job or lose employer coverage (within 8 months). If your employer has fewer than 20 employees, Medicare is primary — you should enroll at 65.

Does Medicare cover prescription drugs?

Original Medicare (Parts A and B) does not cover most outpatient prescription drugs. You need Part D or a Medicare Advantage plan that includes drug coverage. Part D plans cover generic and brand-name drugs, with your costs varying by the plan's formulary and tier structure. As of 2025, out-of-pocket drug costs are capped at $2,000/year.

Can I switch between Original Medicare and Medicare Advantage?

Yes. During the Annual Enrollment Period (October 15 – December 7), you can switch from Original Medicare to Medicare Advantage or vice versa. If you're currently in Medicare Advantage, you can also switch during the Medicare Advantage Open Enrollment Period (January 1 – March 31). Keep in mind that if you switch from Medicare Advantage back to Original Medicare, you may need to apply for a Medigap policy — and medical underwriting may apply if you're past your initial Medigap Open Enrollment Period.

What does Medicare not cover that surprises people most?

The biggest surprises are: long-term nursing home care (Medicare only covers limited skilled nursing, not custodial care), dental care (no routine cleanings, fillings, or dentures), hearing aids, and overseas healthcare. Many people also don't realize that Original Medicare has no annual out-of-pocket maximum — meaning your costs are technically unlimited without supplemental coverage. These gaps are why additional coverage (Medigap, Medicare Advantage, dental plans, long-term care insurance) is so important.

Disclaimer

This article is for educational purposes only and does not constitute insurance advice. Consult a licensed insurance professional for personalized recommendations.

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