Medicare Parts A, B, C & D
Medicare arrives with a set of letters that mean nothing until someone explains them, usually right when you need to make a decision. Here's the plain-language version, before the deadline is bearing down on you.
What Medicare actually is
Medicare is federal health insurance, mainly for people 65 and older (some younger people qualify earlier through disability or certain conditions). It’s not free, and it’s not the same program as Medicaid, which is income-based and run jointly with states. Medicare is something you’ll pay premiums for regardless of your income, though how much depends on which pieces you choose and what you earn.
Those pieces are the four parts (A, B, C, and D), and the decisions about them mostly arrive together, in the months around your 65th birthday.
The four parts, and the two ways to combine them
Parts A and B are often called Original Medicare: A covers hospital stays, B covers doctor visits and outpatient care. Together they’re the foundation, but B leaves a real gap: it generally pays 80% of an approved cost, and there’s no built-in annual limit on the 20% left to you.
From there, most people take one of two paths. The first stays with Original Medicare and fills the gaps: add Part D for prescription drugs, and often a Medigap supplement to cover some or all of that leftover 20%. The second replaces A and B with Part C, Medicare Advantage: a private-insurer plan that usually bundles in drug coverage and adds a yearly out-of-pocket cap, in exchange for using a defined network of doctors and hospitals.
Neither path is universally better. Original Medicare plus Medigap tends to cost more upfront but offers more freedom in who you see; Medicare Advantage tends to cost less upfront but narrows the network and adds more moving pieces to compare each year. Tap through the tool below for what each part actually pays for.
When to enroll, and why the date matters
Your Initial Enrollment Period is seven months long: it starts three months before the month you turn 65, includes your birthday month, and runs three months after. Miss it without other qualifying coverage (typically an active employer group plan) and Part B can carry a permanent premium penalty of roughly 10% for every 12-month period you delayed. Part D has its own, separate late penalty, calculated the same unforgiving way.
If you’re still working past 65 with coverage through a current employer (not retiree coverage, which usually doesn’t count), you can typically delay Part B without a penalty until that coverage ends, but the details depend on the size of the employer, so it’s worth confirming before you assume you’re covered.
Where this fits into the bigger plan
Medicare premiums aren’t flat. Part B and Part D both carry income-based surcharges (IRMAA) determined by your tax return from two years earlier, which means a decision you make at 63, like a large Roth conversion, can raise your Medicare bill at 65. That timing question belongs in the same conversation as your broader retirement income plan, not a separate one held six months later.
We’re glad to walk through how your specific timeline lines up with these dates, no cost, no obligation, and no pressure toward any particular plan.
Try it: what does each part actually cover?
Tap a part to see what it covers and how it's typically paid for.
A Hospital Insurance Inpatient hospital stays
Covers inpatient hospital care, skilled nursing facility stays following a qualifying hospital stay, hospice, and some home health care. Most people get Part A premium-free, because they (or a spouse) paid Medicare payroll taxes for at least 10 years.
B Medical Insurance Doctor visits & outpatient care
Covers outpatient care: doctor visits, preventive screenings, durable medical equipment, and some home health care. Part B carries a monthly premium (higher for higher earners), an annual deductible, and then typically pays 80% of the approved cost, leaving you the other 20% with no built-in cap.
C Medicare Advantage An all-in-one alternative
Not a separate benefit. It's a different way to receive Parts A and B (and usually D), sold through private insurers approved by Medicare. Plans often bundle extras like dental, vision, and hearing, and add an annual out-of-pocket maximum, but usually require using a defined network of providers.
D Prescription Drug Coverage Medications
Covers prescription drugs, through a private insurer's plan. Each plan sets its own list of covered drugs (its formulary) and its own costs, so the right plan depends on what you actually take. Part D can be added to Original Medicare or bundled into many Part C plans.
The two of these usually go together:
Original Medicare
Part A + Part B, often with Part D added for drugs, and sometimes a Medigap supplement to cover the 20% Part B leaves open.
Medicare Advantage
Part C in place of A, B, and usually D: one plan, one card, a defined network, and a yearly cap on what you'd pay.
Educational only: plan availability, costs, and rules vary by state and change yearly. Nothing here is personalized advice, and nothing is saved or sent.
Quick answers
- What do Medicare Parts A, B, C, and D cover?
- Part A covers hospital stays and Part B covers doctor visits and outpatient care; together they are Original Medicare. Part D covers prescriptions, and Part C (Medicare Advantage) replaces A and B with a private plan that usually bundles drug coverage and caps out-of-pocket costs in exchange for a network.
- When do I enroll in Medicare?
- Your Initial Enrollment Period runs seven months: three months before your 65th birthday month, the month itself, and three after. Missing it without qualifying employer coverage can add a permanent premium penalty of roughly 10% to Part B for every 12-month delay.
- Should I choose Medigap or Medicare Advantage?
- Original Medicare plus Medigap tends to cost more upfront with more freedom in who you see; Medicare Advantage tends to cost less upfront with a defined network and yearly comparisons. Moving into Medigap later can require medical underwriting, so the choice deserves care the first time.
- Why does my income affect Medicare premiums?
- Part B and Part D carry income-based surcharges (IRMAA) determined by your tax return from two years earlier, which is why a large Roth conversion at 63 can raise your Medicare bill at 65.
Understanding the topic is one thing. Seeing how it applies to your own plan is another.
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