The Four Parts of Medicare — Quick Overview
Medicare isn't one program — it's four interlocking programs, each covering different services with different costs, enrollment rules, and providers. Understanding each part is critical because enrollment mistakes can result in permanent premium penalties that follow you for the rest of your life. No exaggeration.
Here's the 30-second version: Part A covers hospital stays. Part B covers doctor visits and outpatient care. Part C (Medicare Advantage) is a private-sector alternative that bundles A and B. Part D covers prescription drugs. Now let's dig into the details that actually matter.
Part A: Hospital Insurance
Medicare Part A covers inpatient hospital stays, skilled nursing facility care (following a hospital stay), hospice care, and some home health services. Most people pay $0 in premiums for Part A because they (or their spouse) paid Medicare taxes for at least 10 years (40 quarters) while working.
But "free premiums" doesn't mean "free care." Part A has a deductible of $1,632 per benefit period in 2026. A benefit period starts when 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 within 60 days, it's the same benefit period. If you're readmitted after 60 days, you pay the deductible again.
After the deductible, Part A covers days 1–60 of a hospital stay at $0 cost to you. Days 61–90 cost $408/day in coinsurance. After day 90, you dip into your 60 "lifetime reserve days" at $816/day. Once those are gone, you pay 100% of hospital costs. This is why supplemental coverage (Medigap) matters enormously.
Part B: Medical Insurance
Part B covers doctor visits, outpatient surgery, diagnostic tests, lab work, durable medical equipment, ambulance services, mental health services, and preventive care. Unlike Part A, Part B has a monthly premium — $185/month for most people in 2026, though higher earners pay more through the Income-Related Monthly Adjustment Amount (IRMAA).
Part B has an annual deductible of $257, after which Medicare generally pays 80% and you pay 20% with no out-of-pocket maximum. That last part is crucial: there is no cap on your 20% coinsurance. A $200,000 cancer treatment could leave you owing $40,000. This is the primary reason most Medicare beneficiaries also carry Medigap or Medicare Advantage coverage.
Critical enrollment rule: your Initial Enrollment Period (IEP) for Part B is a 7-month window centered on your 65th birthday month. If you miss it and don't have qualifying employer coverage, you'll face a Late Enrollment Penalty of 10% added to your premium for every 12-month period you could have enrolled but didn't. This penalty never goes away.
Part C: Medicare Advantage
Medicare Advantage plans are offered by private insurance companies approved by Medicare. They must cover everything Part A and Part B cover, and most also include Part D (prescription drug coverage), plus extras like dental, vision, hearing, and fitness benefits that Original Medicare doesn't cover.
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The trade-off: Advantage plans use provider networks (HMOs, PPOs) that restrict which doctors and hospitals you can use. Original Medicare lets you see any provider that accepts Medicare — roughly 97% of all physicians nationally. Advantage plans also have annual out-of-pocket maximums (unlike Original Medicare), which provides important financial protection.
About 51% of Medicare beneficiaries are now enrolled in Advantage plans, up from 19% a decade ago. The plans are particularly popular in areas with robust healthcare networks. However, be cautious about switching from Original Medicare + Medigap to an Advantage plan: if you later want to switch back, you may not be able to get Medigap coverage without medical underwriting, depending on your state.
Part D: Prescription Drug Coverage
Part D covers prescription medications through private insurance plans approved by Medicare. Plans vary significantly in which drugs they cover (their "formulary"), how much they charge in copays and coinsurance, and which pharmacies are in-network. Monthly premiums typically range from $7 to $100+ depending on the plan.
Part D has a coverage gap known as the "donut hole." In 2026, after you and your plan have spent $5,030 on covered drugs, you enter the gap. During this phase, you'll pay no more than 25% of the cost for brand-name and generic drugs. Once your out-of-pocket spending reaches $8,000, you enter catastrophic coverage, where your costs drop to $0 for the rest of the year.
Like Part B, Part D has a Late Enrollment Penalty: 1% of the national base premium ($34.70 in 2026) for every month you were eligible but didn't enroll and didn't have creditable drug coverage elsewhere. Over years, this adds up substantially.
Enrollment Periods and Late Penalties
Timing is where Medicare punishes the unprepared. Your Initial Enrollment Period spans the seven months around your 65th birthday. Miss it without qualifying coverage and the penalties can be permanent: the Part B late-enrollment penalty adds 10% to your premium for each full year you delayed — for life — and Part D carries its own lifelong penalty. If you are still working with employer coverage at 65, understand how that interacts with Medicare before you delay, so you do not trigger a penalty by accident.
Don't Forget Medigap
Original Medicare (Parts A and B) has no out-of-pocket maximum, so a serious illness can expose you to large costs. Medigap (Medicare Supplement) plans, sold by private insurers, fill those gaps — deductibles, copays, and coinsurance. Crucially, your strongest guaranteed right to buy any Medigap policy regardless of health is a one-time six-month window that opens when you first enroll in Part B. Miss it and insurers can later charge you more or deny coverage based on your health, so this is a deadline worth marking.
Choosing the Right Medicare Path
The decision comes down to two paths: Original Medicare (Parts A + B) with a standalone Part D plan and possibly a Medigap supplement, or Medicare Advantage (Part C), which bundles everything into one plan. Neither path is universally better — it depends on your health needs, preferred doctors, prescription drugs, travel habits, and budget.
Our recommendation: review your options during the Annual Enrollment Period (October 15 – December 7) every year. Use Medicare.gov's Plan Finder tool to compare specific plans in your area, and don't assume last year's best plan is still the best choice — formularies, premiums, and networks change annually.
The Medicare Part B and Part D Late Enrollment Penalties
If you fail to sign up for Medicare Part B when you first become eligible at age 65 (and do not have qualifying active employer coverage), you incur a permanent 10% Part B premium penalty for every 12-month period you were eligible but un-enrolled. This penalty is added to your monthly Part B bill for the rest of your life.
IRMAA Surcharges for High-Income Seniors
Higher-income Medicare beneficiaries pay additional monthly surcharges on Part B and Part D premiums known as Income-Related Monthly Adjustment Amounts (IRMAA). IRMAA thresholds are calculated using Modified Adjusted Gross Income (MAGI) from your tax return 2 years prior ($103,000+ single / $206,000+ joint), increasing Part B premiums by $70 to $400+/month.
Medigap Medical Underwriting Rules Outside Guaranteed Issue Windows
When you first turn 65 and enroll in Medicare Part B, you get a 6-month Medigap Open Enrollment Period where private insurers must sell you any policy regardless of health conditions. Once that 6-month window expires, insurers in most states apply strict medical underwriting, and can deny Medigap coverage for pre-existing conditions.
Understanding the Medicare Part D Prescription Donut Hole
Under recent Inflation Reduction Act reforms, the old Medicare Part D "Donut Hole" coverage gap is replaced by an absolute $2,000 Annual Out-of-Pocket Cap on Prescription Drugs starting in 2025, protecting seniors taking high-cost brand-name specialty medications.
Understanding the Medicare Part A Inpatient Hospital Deductible
Unlike traditional insurance deductibles that apply per calendar year, the Medicare Part A deductible ($1,632 for 2026) applies per benefit period. A new benefit period begins once you have been out of a hospital or skilled nursing facility for 60 consecutive days.
Understanding Medicare Part D Preferred Pharmacy Networks
Medicare Part D prescription plans utilize Preferred Pharmacy Networks. Filling maintenance prescriptions at designated preferred retail or mail-order pharmacies significantly reduces prescription copays compared to non-preferred network pharmacies.
The Role of State Pharmaceutical Assistance Programs (SPAP)
Low-income seniors who exceed Medicaid qualification caps can utilize **State Pharmaceutical Assistance Programs (SPAP)** available in over 20 states. SPAP programs coordinate alongside Medicare Part D to pay secondary prescription copays and annual Part D plan deductibles.
Understanding the Medicare Part A Inpatient Hospital Deductible
Unlike traditional health plan deductibles that reset per calendar year, the Medicare Part A deductible ($1,632 for 2026) applies **per benefit period**, which begins the day you enter a hospital and ends when you have been out of care for 60 consecutive days.
Reviewing annual Medicare Plan Annual Notice of Change (ANOC) documents every October allows beneficiaries to adjust prescription drug plans and Medigap coverage before open enrollment deadlines.
Understanding these essential coverage guidelines helps you optimize long-term financial security and make informed decisions for your family.
Medicare Coverage Gaps: What Parts A & B Do NOT Pay For
Many seniors are surprised to discover that Original Medicare (Parts A & B) leaves major healthcare categories completely uncovered. Original Medicare does NOT pay for:
- Routine Dental Care: Cleanings, fillings, root canals, dentures, and dental implants.
- Routine Vision & Eyeglasses: Eye exams, frames, lenses, and contact lenses (except following cataract surgery).
- Hearing Aids: Audiologist exams and hearing aid hardware ($3,000 to $6,000 out-of-pocket costs).
- Long-Term Custodial Care: Non-skilled assistance with daily living (bathing, dressing) in nursing homes or home settings.
- Foreign Travel Emergency Care: Healthcare received outside the United States (except limited emergency coverage under certain Medigap plans C through N).
Filling these coverage gaps requires enrolling in private Medicare Advantage plans with dental/vision/hearing riders, buying standalone dental/vision policies, or maintaining dedicated health savings reserves.
Related Reading: Check out our in-depth Health Insurance Deductible Guide for step-by-step guidance.
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