Medicare 101: the whole system, taught simply.
Consider this your friendly crash course. In a few minutes you’ll understand what Medicare is, who qualifies, what each part does, how the pieces fit together, and the handful of terms that unlock everything else. No jargon left unexplained — and no pressure.
What Medicare is — and who qualifies
Medicare is the federal health insurance program primarily for people 65 and older, plus certain younger people with disabilities or specific conditions. It’s run by the government, funded partly by the taxes you’ve paid over your working life. Here’s who becomes eligible and when.
Age 65
The main path. Most people qualify at 65, whether or not they’re retired — and many get Part A premium-free based on their work history.
Under 65 with a disability
People receiving Social Security disability benefits generally become eligible after a set waiting period.
End-Stage Renal Disease
Those with permanent kidney failure requiring dialysis or a transplant can qualify at any age.
ALS
People diagnosed with ALS (Lou Gehrig’s disease) qualify as soon as their disability benefits begin.
Some people are enrolled in Parts A and B automatically (for example, if you’re already drawing Social Security), while others must sign up on their own. Knowing which one is you — and when — is the whole game. We’ll tell you for free.
The four parts, and what each covers
Medicare is built from four parts. Parts A and B are “Original Medicare” from the government; Parts C and D are private. Here’s what each one does — and doesn’t.
- Inpatient hospital stays
- Skilled nursing facility care
- Hospice care
- Some home health care
- Long-term custodial care
- Most care outside a facility
- Doctor and specialist visits
- Outpatient care and surgery
- Preventive screenings
- Lab tests and equipment
- Prescription drugs (that’s Part D)
- Routine dental, vision, hearing
- Everything in Parts A & B
- Usually prescription drugs
- Often dental, vision, hearing
- A yearly out-of-pocket cap
- Usually uses a network
- Referrals may be required
- Prescription medications
- Each plan has its own drug list
- Available stand-alone or bundled
- Delaying it can bring a penalty
- Drug lists differ by plan
How the pieces fit together
Here’s the mental model: everyone starts with Original Medicare (A & B). Because it has gaps, you complete your coverage one of two ways — you don’t do both.
The foundation
Original Medicare (Parts A & B) pays a large share of your care, but leaves deductibles and a 20% coinsurance with no yearly limit.
Path 1: add to it
Keep Original Medicare and add a Medigap supplement plus a Part D drug plan. Freedom to see any doctor, very predictable costs.
Path 2: replace it
Choose a Medicare Advantage plan that bundles A, B, and usually D — often with extras, usually with a network.
You can’t use a Medigap policy with a Medicare Advantage plan — it’s one path or the other. Which fits depends on your doctors, prescriptions, and budget. See both paths compared →
The key terms that unlock everything
Medicare has its own vocabulary. Learn these fifteen and the plans, charts, and fine print suddenly make sense.
How enrollment works
Medicare runs on specific windows. Knowing which one applies to you — and not missing it — is the difference between smooth sailing and a lifelong penalty.
Initial Enrollment Period
Your first 7-month window — the 3 months before your birthday month, that month, and the 3 months after.
Medigap Open Enrollment
A one-time 6-month window (starting at 65 and on Part B) to buy any supplement with no health questions.
Annual Enrollment Period
Each year, change your Medicare Advantage or Part D coverage for the year ahead.
Advantage Open Enrollment
Already in an Advantage plan? One yearly chance to switch or return to Original Medicare.
Most people apply online with Social Security, by phone, or in person. If you delayed Part B because you were still working, you’ll use two official forms — CMS-40B (to enroll in Part B) and CMS-L564 (proof of your employer coverage). We walk you through every step and the exact forms on our How to Apply for Medicare guide, and you can review all the windows on the Medicare Enrollment Periods page.
Where to go next
You’ve got the fundamentals. Here’s every guide and tool to take you the rest of the way — organized by what you need.
New to Medicare
Your step-by-step roadmap and timeline for getting started.
Start the roadmapWhat Is Medicare
The basics in plain English — the four parts and how they fit.
Read the guideMedicare Eligibility
Find out exactly when you qualify — by age, disability, or condition.
Check eligibilityHow to Apply for Medicare
Step-by-step, with the official CMS forms you can download.
How to applyEnrollment Periods
Every window explained so you never miss a deadline or penalty.
See the windowsMedicare Costs
Premiums, deductibles, and the IRMAA income surcharge for this year.
Understand costsMedicare & Employer Coverage
Still working past 65? How Medicare works with a job or spouse’s plan.
Working past 65How to Choose a Plan
Supplement or Advantage? How to pick what actually fits you.
Choose a planMistake Risk Checker
Find out which costly Medicare mistakes you’re most at risk of.
Check my riskSupplement vs. Advantage
What Is a Medicare Supplement
How Medigap works and how every lettered plan compares.
Read the guideAdvantage vs. Medigap
The two paths compared head to head on cost, freedom, and networks.
Compare pathsBest Medigap by Health Profile
Which supplement fits your health, budget, and priorities best.
Find your planMedigap A–N Comparison
Every lettered supplement plan, compared side by side.
Compare plansPlan G vs N vs HD-G
The most popular supplements, compared in plain English.
See the differenceMedicare Plans Explained
The four parts and two paths compared, side by side.
Read the guideCheck yourself in minutes
Now that you know the basics, let’s make it personal.
Understanding Medicare is step one — choosing the right plan for your doctors, prescriptions, and budget is step two. Tell us about your situation and we’ll compare every option that fits, free of charge and free of bias.