Medicare is the federal health insurance program for Americans 65 and older (and some younger people with disabilities). With over 67 million enrollees, it’s one of the largest health insurance programs in the world — and one of the most confusing.
Understanding Medicare isn’t optional if you’re approaching 65. Miss the enrollment deadline, and you’ll pay a penalty that lasts for life. Choose the wrong plan, and you could pay thousands more than necessary or find yourself without coverage when you need it most.
This guide cuts through the complexity. We’ll explain what each part covers, what it actually costs, and the critical deadlines you can’t afford to miss. Whether you’re planning ahead for retirement or helping a parent navigate their options, this is what you need to know.
How Medicare Works: The Four Parts
Medicare is divided into four “parts,” each covering different services. The naming is unintuitive (Parts A, B, C, D), but here’s the quick version:
- Part A (Hospital) — Covers inpatient hospital stays, skilled nursing, hospice. Most people pay $0 premium.
- Part B (Medical) — Covers doctor visits, outpatient care, preventive services. Everyone pays a premium ($185/month standard).
- Part C (Medicare Advantage) — Private insurance that bundles A + B + usually D. Alternative to “Original Medicare.”
- Part D (Prescription Drugs) — Covers medications. Separate plan unless you have Part C.
Most people get Part A automatically at 65 if they’re receiving Social Security benefits. Part B requires active enrollment and has consequences if you miss deadlines.
Medicare Parts at a Glance
| Part | What It Covers | Monthly Premium (2026) | Deductible |
|---|---|---|---|
| Part A (Hospital) | Inpatient hospital, skilled nursing, hospice | $0 (most people)* | $1,676/benefit period |
| Part B (Medical) | Doctor visits, outpatient care, preventive services | $185 (standard) | $257/year |
| Part C (Medicare Advantage) | Parts A + B + usually D, often extras | $0-$50 (on top of Part B) | Plan-specific |
| Part D (Drug Coverage) | Prescription medications | $35-$45 average | $545/year |
*Free if you or your spouse worked 40+ quarters (10 years) paying Medicare taxes.
The critical point: Parts A and B together are called “Original Medicare” — the government-run program. Part C (Medicare Advantage) is an alternative offered by private insurers. Most people choose one path or the other, not both. For a detailed comparison, see Medicare Advantage vs Original Medicare.
Medicare Coverage Details
Part A: Hospital Insurance
Part A covers inpatient care — situations where you’re formally admitted to a hospital or skilled nursing facility. It does NOT cover outpatient surgeries, doctor visits, or preventive care (that’s Part B).
| Service | Medicare Pays | You Pay |
|---|---|---|
| Hospital stay (days 1-60) | All but deductible | $1,676 deductible |
| Hospital stay (days 61-90) | All but coinsurance | $419/day |
| Hospital stay (days 91-150, lifetime reserve) | All but coinsurance | $838/day |
| Skilled nursing facility (days 1-20) | 100% | $0 |
| Skilled nursing facility (days 21-100) | All but coinsurance | $209.50/day |
| Home health services | 100% (if medically necessary) | $0 |
| Hospice care | 100% (most services) | Small copays for drugs |
The $1,676 hospital deductible isn’t per year — it’s per “benefit period.” A benefit period starts when you’re admitted 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, you pay the deductible again.
Skilled nursing coverage is limited. Medicare pays 100% only for the first 20 days, and only if you’ve had a qualifying hospital stay of 3+ nights. This is NOT long-term care — Medicare doesn’t cover nursing home stays for custodial care.
Part B: Medical Insurance
Part B covers outpatient care — doctor visits, preventive services, lab tests, outpatient surgery, and durable medical equipment. This is where most of your routine healthcare happens.
| Service | Medicare Pays | You Pay |
|---|---|---|
| Doctor visits | 80% after deductible | 20% + $257 annual deductible |
| Outpatient surgery | 80% after deductible | 20% |
| Lab tests | 100% | $0 |
| Preventive care (annual wellness, screenings) | 100% | $0 |
| Durable medical equipment | 80% | 20% |
| Mental health (outpatient) | 80% after deductible | 20% |
| Ambulance | 80% after deductible | 20% |
The 20% coinsurance has no cap. Unlike most health insurance, Original Medicare has no out-of-pocket maximum. If you have a $100,000 surgery, you owe $20,000 (20%). This is why many people add a Medigap supplemental policy or choose Medicare Advantage (which has caps). See our Medigap vs Medicare Advantage comparison.
Preventive care is free — but only when billed as preventive. Your annual wellness visit is $0, but if you discuss a new symptom and it becomes a diagnostic visit, you may owe the 20% coinsurance. Always clarify with your doctor’s office.
Part D: Prescription Drug Coverage
Part D covers prescription medications and works differently than hospital or medical coverage. For a complete breakdown, see our Medicare Part D guide.
| Coverage Phase | 2026 Structure |
|---|---|
| Deductible | $545 |
| Initial coverage | 25% copay (plan pays 75%) |
| Coverage gap (“donut hole”) | Drug companies discount 75%; you pay 25% for brand-name |
| Catastrophic coverage | $0 out-of-pocket after $2,000 max |
2026 change: The Inflation Reduction Act capped total out-of-pocket drug costs at $2,000/year.
This $2,000 cap is a game-changer. Before 2025, seniors with expensive medications could pay $10,000+ annually for drugs. Now, once you hit $2,000 in out-of-pocket costs for the year, Part D covers 100% of additional drug costs. This makes Medicare significantly more affordable for people with cancer, rheumatoid arthritis, MS, and other conditions requiring expensive medications.
Medicare Advantage (Part C) vs. Original Medicare
This is the biggest decision you’ll make: stick with government-run Original Medicare (Parts A + B) and add a separate drug plan, or choose a private Medicare Advantage plan that bundles everything together.
| Feature | Original Medicare (A + B) | Medicare Advantage (Part C) |
| Feature | Original Medicare (A + B) | Medicare Advantage (Part C) |
|---|---|---|
| Network | Any doctor that accepts Medicare | Usually HMO or PPO network |
| Out-of-pocket maximum | No cap | Capped (typically $3,000-$8,000) |
| Extra benefits | None (unless you add Medigap) | Often includes dental, vision, hearing, fitness |
| Drug coverage | Separate Part D plan needed | Usually included |
| Monthly premium | Part B ($185) + Medigap ($150-$300) | Part B ($185) + $0-$50 |
| Referral needed | No | Sometimes (HMO plans) |
| Travel coverage | Limited outside US | Usually limited to network area |
| Cost predictability | Less predictable (20% coinsurance is uncapped) | More predictable (annual cap) |
Which Should You Choose?
Choose Original Medicare + Medigap if:
- You travel frequently or split time between states
- You want maximum doctor/hospital choice
- You can afford Medigap premiums ($150-$300/month extra)
- Your health is complex and you need specialists
Choose Medicare Advantage if:
- You want dental, vision, and hearing included
- You prefer predictable costs with an out-of-pocket cap
- You’re comfortable with a network of doctors
- You want lower monthly premiums
About 54% of Medicare beneficiaries now choose Medicare Advantage — up from 19% in 2007. The extra benefits (dental, vision, gym memberships) are attractive, but read the network restrictions carefully.
Enrollment Deadlines
This section is critical. Medicare penalties are real, permanent, and financially devastating. Missing your enrollment window by even a few weeks can cost you thousands over your lifetime.
| Period | When | What You Can Do |
|---|---|---|
| Initial Enrollment | 3 months before to 3 months after turning 65 | Enroll in Parts A, B, C, D |
| General Enrollment | Jan 1 - Mar 31 each year | Enroll in Part B (with penalty) |
| Open Enrollment (AEP) | Oct 15 - Dec 7 each year | Switch Advantage plans or Part D |
| Medicare Advantage Open Enrollment | Jan 1 - Mar 31 each year | Switch Advantage plans or go to Original |
| Special Enrollment | After qualifying life event | Various changes |
When Your Initial Enrollment Period Starts
Your Initial Enrollment Period (IEP) is a 7-month window centered on your 65th birthday month:
- 3 months before your birthday month
- Your birthday month
- 3 months after your birthday month
If your birthday is July 15, your IEP runs April 1 through October 31. Sign up in the first 3 months to ensure coverage starts on your birthday. Sign up later, and coverage may be delayed.
The Exception: Employer Coverage
If you’re still working at 65 with employer health insurance (for yourself, not COBRA), you can delay Medicare Part B without penalty. Your Special Enrollment Period starts when you leave the job or lose coverage — you have 8 months to enroll.
Get a form from HR. When you do enroll, you’ll need a Certificate of Creditable Coverage from your employer proving you had continuous coverage. Missing this paperwork can cause delays.
Late Enrollment Penalties
| Part | Penalty | Duration |
|---|---|---|
| Part A | 10% higher premium for 2× years you were eligible but didn’t enroll | Temporary |
| Part B | 10% higher premium for each 12-month period you were eligible but didn’t enroll | Permanent (for life) |
| Part D | 1% of national base premium × months without coverage | Permanent |
Example: If you delay Part B by 3 years, you pay a 30% penalty on your premium for life. At $185/month, that’s $55.50/month extra—forever.
Real-world impact: Someone who delayed Part B by 5 years pays $92.50/month extra for life. Over 20 years, that’s $22,200 in penalties — for simply missing a deadline.
Income-Related Monthly Adjustment Amount (IRMAA)
High earners pay more for Part B and Part D. This is called IRMAA (Income-Related Monthly Adjustment Amount), and it’s based on your tax return from two years prior — not current income.
If you retire and your income drops significantly, you can request an IRMAA recalculation using SSA Form 44. Qualifying life events include retirement, divorce, death of a spouse, loss of income-producing property, or loss of pension.
| Individual Income (2024 Tax Return) | Joint Income | Part B Premium (2026) | Part D Surcharge |
|---|---|---|---|
| $106,000 or less | $212,000 or less | $185.00 | $0 |
| $106,001-$133,000 | $212,001-$266,000 | $259.00 | $13.70 |
| $133,001-$167,000 | $266,001-$334,000 | $370.00 | $35.30 |
| $167,001-$200,000 | $334,001-$400,000 | $480.90 | $57.00 |
| $200,001-$500,000 | $400,001-$750,000 | $591.90 | $78.60 |
| Above $500,000 | Above $750,000 | $628.90 | $85.80 |
IRMAA planning tip: If you’re near a threshold, consider strategies like Roth conversions before age 63 (so the higher income doesn’t show on the tax return used for IRMAA calculations at 65). Or delay large capital gains realizations until after Medicare enrollment stabilizes.
What Medicare Doesn’t Cover
Medicare has significant gaps. These services are NOT covered:
- Long-term care / nursing home stays (custodial care)
- Most dental care (cleaning, fillings, dentures)
- Eye exams for glasses (exams for disease are covered)
- Hearing aids and exams for hearing aids
- Cosmetic surgery
- Care outside the United States
This is why average retirement healthcare costs often exceed $300,000 per couple — Medicare doesn’t cover everything, and what it does cover requires premiums, deductibles, and coinsurance.
The Bottom Line
Enroll in Medicare on time to avoid lifetime penalties. Most people need Part A (free), Part B ($185/month), and either a Medigap supplement or Medicare Advantage plan. The 2026 $2,000 annual cap on drug costs is a major benefit.
If you’re still working at 65 with employer coverage, you can delay Part B without penalty — but get the timing right with your HR department. And remember: the decision between Original Medicare and Medicare Advantage isn’t permanent. You can switch during the annual Open Enrollment Period (October 15 - December 7) each year.
Key dates to remember:
- 3 months before age 65: Begin Initial Enrollment Period
- Your 65th birthday month: Coverage can start if you enrolled in the first 3 months
- 3 months after age 65: End of Initial Enrollment Period
- October 15 - December 7: Annual Open Enrollment to switch plans
Related: Medicare vs Medicaid | Medicare Part D Guide | Medicare Advantage vs Original Medicare | Medigap vs Medicare Advantage | When to Claim Social Security | Social Security Benefits Guide