Medicare Parts A, B, C, and D: A Straightforward Guide

Medicare can feel confusing when you first hear about Parts A, B, C, and D. Each “part” covers different types of care, has different costs, and is managed in slightly different ways.

This guide from HowToGetAssistance.org is meant to explain Medicare in plain English so you can better understand your options before you contact an official office or benefits portal. This site is not a government agency, not a Medicare plan, and not an enrollment website.

What Is Medicare, in Simple Terms?

Medicare is a federal health insurance program primarily for:

• People age 65 and older
• Some younger people with certain disabilities
• People with End-Stage Renal Disease (ESRD) or certain other qualifying conditions

Medicare is divided into four main parts:

• Part A – Hospital insurance
• Part B – Medical insurance
• Part C – Medicare Advantage (private plans that bundle Parts A and B, often extras)
• Part D – Prescription drug coverage

You do not have to take every part. Many people start with Original Medicare (Parts A and B) and then decide whether to add Part C (Medicare Advantage) or Part D (drug coverage), or other supplemental coverage.

Quick Comparison: Medicare Parts A, B, C, and D

Use this simple table to see how the parts differ at a glance:

Medicare Part A: Hospital Insurance

What Part A Usually Covers

Medicare Part A helps with the big, hospital-related costs. In general, it may cover:

• Inpatient hospital stays (room, meals, and some services)
• Skilled nursing facility care (after a qualified hospital stay, and under specific conditions)
• Some home health care ordered by a doctor
• Hospice care for people with a terminal illness who qualify

Part A does not pay for everything during a hospital stay. There can be deductibles, coinsurance, and limits on how many days are covered.

Who Typically Gets Part A and When

Most people:

• Become eligible at age 65
• Qualify for premium-free Part A if they or a spouse worked and paid Medicare taxes for a certain number of quarters
• May enroll automatically if they are already receiving Social Security or Railroad Retirement Board benefits before turning 65

People with certain disabilities or specific medical conditions may qualify earlier.

If you are not automatically enrolled, you can typically sign up through:

• The Social Security Administration (online, phone, or local office)
• The Railroad Retirement Board, if that applies to you

The exact process can vary slightly depending on your situation.

Documents to Have Ready for Part A

When you contact an official office to enroll, it helps to have:

• Photo ID (driver’s license, state ID, or passport)
• Social Security number
• Proof of age, if needed (birth certificate or other official record)
• Work history details, especially if you or a spouse may qualify for premium-free Part A
• Information about any current health insurance you have (employer, union, or other coverage)

Medicare Part B: Medical Insurance

What Part B Usually Covers

Medicare Part B helps with routine and outpatient care, often including:

• Doctor and specialist visits
• Outpatient services (like certain surgeries, lab work, X-rays)
• Preventive services (screenings, some vaccines, annual wellness visits)
• Durable medical equipment (such as walkers, wheelchairs, certain home medical devices) when medically necessary
• Certain home health services ordered by a doctor

Part B has:

• A monthly premium
• A yearly deductible
• Coinsurance (for example, paying a percentage of approved charges after the deductible)

Who Typically Enrolls in Part B

Most people choose to sign up for Part B when they’re first eligible because:

• If you delay Part B without having qualifying job-based coverage, you may face a late enrollment penalty and gaps in coverage
• If you or your spouse are still working and covered by an employer or union plan, you may have some options to delay Part B without a penalty, depending on the size and rules of the employer plan

Because this can be complicated, many people:

• Contact the Social Security Administration
• Reach out to their employer benefits office
• Call the official Medicare helpline for clarification before making a decision

Documents to Gather for Part B Enrollment

You may need:

• Identification and Social Security number
• Details about your current health coverage (employer or union plan)
• If you’re delaying Part B due to employer coverage, often:
  • Employer verification forms confirming your coverage
  • Dates you were covered

These forms are usually available from the official Medicare or Social Security channels, or from your employer’s benefits department.

Medicare Part C: Medicare Advantage Plans

What Is Medicare Part C?

Medicare Part C, also called Medicare Advantage, is an alternative way to receive Medicare benefits.

Instead of getting your coverage directly from the federal program under Original Medicare (Parts A and B), you can choose to get it through a private insurance company that has a contract with Medicare.

A typical Medicare Advantage plan:

• Must provide at least the same coverage as Part A and Part B
• Often includes Part D (prescription drugs)
• May include extra benefits, like:
  • Limited dental coverage
  • Vision services and eyeglasses
  • Hearing exams and hearing aids
  • Fitness or wellness programs
• Uses provider networks (such as HMOs or PPOs), which may limit which doctors and hospitals you can use at the lowest cost

Key Things to Know About Part C

• You usually must have both Part A and Part B to join a Medicare Advantage plan.
• You still pay your Part B premium, and sometimes an additional premium to the plan.
• Out-of-pocket costs and coverage rules can vary widely from plan to plan.
• Many plans require you to see network providers or get referrals for specialists.

When and How People Commonly Enroll in Part C

Most people consider Part C during:

• The Initial Enrollment Period around their 65th birthday (a 7-month window)
• The Medicare Open Enrollment Period (annually in the fall)
• A Special Enrollment Period, if they qualify due to certain life events (like moving out of a plan’s service area or losing other coverage)

To compare and enroll in Medicare Advantage plans, people commonly:

• Use the official Medicare plan finder tool online (on the government website)
• Call the official Medicare helpline
• Contact licensed insurance agents who sell Medicare Advantage plans
  • If you do this, it’s important to confirm they are properly licensed and that you understand they may only show certain companies’ plans.

Questions to Ask Before Choosing a Medicare Advantage Plan

Before deciding, it can help to ask:

• Are my current doctors and hospitals in the plan’s network?
• Are my prescriptions covered, and at what cost tier?
• What are the copays for primary care and specialists?
• What is the annual out-of-pocket maximum?
• Are extra benefits (dental, vision, hearing, etc.) truly helpful for my situation, or just marketing?

Medicare Part D: Prescription Drug Coverage

What Part D Usually Covers

Medicare Part D helps pay for outpatient prescription medications.

Plans are offered by private insurance companies approved by Medicare. Each Part D plan has:

• Its own list of covered drugs (called a formulary)
• Different tiers that affect how much you pay for each medication
• A monthly premium
• Possible deductibles, copays, and coinsurance

Medications taken during a hospital inpatient stay are usually covered under Part A or Part B, not Part D.

Who Typically Needs Part D

Generally, you consider Part D if:

• You have Original Medicare (Parts A and B) and need medicine on a regular basis
• Your employer or union coverage does not include prescription drug coverage, or you’re losing that coverage
• You want protection against high drug costs in the future, even if you don’t take many medications now

If you go too long without creditable drug coverage (coverage that’s at least as good as standard Part D) after you’re first eligible, you may face a late enrollment penalty if you sign up later.

How People Usually Enroll in Part D

You can get Part D in two main ways:

1. Stand-alone Part D plan

   • Works with Original Medicare (A and B)
   • You enroll in a separate prescription drug plan

2. Part D included inside a Medicare Advantage plan (Part C)

   • Many Medicare Advantage plans already include drug coverage

To sign up, people typically:

• Use the official Medicare website to compare plans by premium, drug list, and pharmacy network
• Call the official Medicare helpline for assistance
• Contact plan companies directly through their official phone lines

Original Medicare vs. Medicare Advantage (Part C)

A common source of confusion is deciding between:

• Original Medicare (Parts A and B), often plus:
  • A stand-alone Part D plan
  • Optional supplement (Medigap) coverage, which is separate, private insurance that may help pay some out-of-pocket costs

versus

• Medicare Advantage (Part C), which usually bundles:
  • Part A
  • Part B
  • Often Part D
  • Sometimes extra benefits

Basic Comparison

Original Medicare (A & B):

• You can see any doctor or hospital that accepts Medicare nationwide.
• You may add Part D for prescriptions.
• You may buy a Medigap policy from a private company to help with copays, coinsurance, and deductibles (availability and rules vary by state).
• There is no single out-of-pocket maximum, but Medigap can help manage costs if you choose to purchase it.

Medicare Advantage (C):

• Usually has networks (you may pay more or lose coverage if you go out-of-network, depending on the plan type).
• Often includes Part D and extra benefits (dental, vision, hearing, etc.).
• Must include at least same basic coverage as Original Medicare.
• Usually has an annual out-of-pocket maximum for covered services, but cost-sharing and rules vary by plan.

Because this choice can affect your access to doctors, medications, and long-term costs, many people:

• Speak with State Health Insurance Assistance Programs (SHIPs), which typically offer free, unbiased counseling
• Call the official Medicare helpline
• Review plan documents carefully before enrolling or switching

Who Typically Qualifies for Medicare (General Overview)

Most people qualify for Medicare if:

• They are 65 or older and
  • Are a U.S. citizen, or
  • Are a lawful permanent resident who has met required residency periods
• Or they qualify earlier because of:
  • Certain disabilities, usually after receiving Social Security disability benefits for a specific period
  • End-Stage Renal Disease (ESRD) or certain other qualifying conditions

Because individual eligibility can be complex, especially for those under 65, people usually confirm their status directly with:

• The Social Security Administration
• The Railroad Retirement Board, if applicable
• The official Medicare helpline

Common Timeframes and Deadlines to Know

Understanding the typical enrollment windows can help you avoid penalties and coverage gaps.

1. Initial Enrollment Period (IEP)
For most people turning 65, this is a 7-month window:

• 3 months before the month you turn 65
• The month you turn 65
• 3 months after that month

During this period, you typically can:

• Enroll in Part A (and Part B, if you choose)
• Choose a Medicare Advantage (Part C) or Part D plan

2. General Enrollment Period (GEP)
If you miss your Initial Enrollment Period and do not qualify for a Special Enrollment Period, there is usually a General Enrollment Period each year when you can sign up for Part A and/or Part B. Late enrollment penalties may apply.

3. Medicare Advantage and Part D Open Enrollment (Annual Election Period)
Each year, there is a fall Open Enrollment Period when people with Medicare can:

• Switch from Original Medicare to a Medicare Advantage plan
• Switch from Medicare Advantage back to Original Medicare
• Change Part D drug plans

4. Special Enrollment Periods (SEPs)
You may qualify for a Special Enrollment Period if you:

• Move out of your plan’s service area
• Lose other qualifying coverage (like employer-sponsored coverage)
• Experience certain other qualifying events

Because rules change and details matter, it’s helpful to confirm current dates and rules through official channels.

What Happens After You Enroll

Once you successfully enroll through an official office or portal:

• You typically receive a Medicare card in the mail for Parts A and B.
• If you joined a Medicare Advantage or Part D plan:
  • You usually receive a plan ID card and coverage materials explaining:
    • Copays
    • Network rules
    • Covered medications
• You start paying premiums (if any) and using your coverage as of the effective date given to you.

If there is a delay or problem:

• You can contact the Social Security Administration (for Part A and B issues)
• You can contact the plan’s member services (for Part C or D plans)
• You may also contact the official Medicare helpline for further guidance

Common Reasons for Delays or Denials

People sometimes face delays or complications with Medicare-related coverage for reasons such as:

• Missing or incorrect information on enrollment forms
• Uncertain work history or residency details
• Enrolling outside an eligible timeframe without a qualifying Special Enrollment Period
• Choosing a Medicare Advantage or Part D plan that:
  • Doesn’t serve their geographic area
  • Doesn’t cover specific medications they need
• Not understanding that certain services are not covered or require prior authorization

If you receive a denial notice for a service, claim, or medication, the notice usually includes information about:

• Why it was denied
• How to appeal
• Deadlines for filing an appeal

Appeals typically have several levels, and you generally start by:

• Contacting the plan (for Part C or D) or
• Following instructions on official Medicare decision notices (for Original Medicare claims)

How Medicare Appeals Usually Work

If Medicare or your plan denies coverage for a service, item, or medication, you often have the right to appeal. At a basic level, the process usually includes:

1. Review the denial notice carefully

   • Understand the reason for denial and the deadline to appeal.

2. Gather supporting documents, such as:

   • Letters from your doctor
   • Medical records
   • Any relevant billing or policy information

3. Submit the appeal according to instructions on the notice, which might involve:

   • Mailing forms to a specific address
   • Using your plan’s online portal (for Part C or D)
   • Calling the plan’s member services line for guidance

4. If the first-level appeal is denied, there are often additional levels of appeal available through official Medicare channels.

Because appeals can be time-sensitive and detailed, many people seek help from:

• State Health Insurance Assistance Programs (SHIPs)
• Local legal aid organizations, when available
• The official Medicare helpline

Alternatives and Additional Help if You Don’t Qualify or Need Extra Support

If you do not qualify for certain parts of Medicare yet, or if costs are too high, some options people commonly explore include:

• Medicaid – A state and federal program that helps with medical costs for people with limited income and resources.

  • Some people have both Medicare and Medicaid, sometimes called “dual eligible.”
  • You can usually apply through your state Medicaid agency or county human services office.

• Medicare Savings Programs – State-run programs that may help pay Part A and/or Part B premiums, and sometimes other costs, for people with limited income and assets.

  • Applications are usually handled by your state’s Medicaid office or other state benefit agency.

• Extra Help (Low-Income Subsidy) for Part D – A federal program that may help pay Part D premiums, deductibles, and co-pays for prescription drugs.

  • People usually apply through the Social Security Administration or their state Medicaid agency.

• Employer or Union Retiree Coverage – Some people have access to retiree health benefits that work with or instead of certain parts of Medicare.

• Community Health Centers and Clinics – These may offer services on a sliding fee scale based on income, sometimes even if you are uninsured or underinsured.

For detailed eligibility and application steps, you generally need to contact:

• Your state Medicaid office
• Your local Department of Human Services (or similar agency)
• The Social Security Administration

How to Make Sure You’re Using Official Medicare Channels

Because Medicare is well-known, it can also attract scams or misleading marketing. To protect yourself:

• Check the web address
  • Official U.S. government Medicare information is on websites that end in “.gov”.
• Be cautious with unsolicited calls, emails, or door-to-door visits
  • Medicare typically does not call you out of the blue to ask for your Medicare number, Social Security number, or banking information.
• Verify plan representatives
  • If someone claims to represent a Medicare Advantage or Part D plan, you can:
    • Ask for their full name and license number
    • Call the plan’s official member services number (found on the plan’s published materials or the official Medicare website) to verify.
• Never give payment information just to receive information or to “hold” a spot.
• For general questions or to report suspected scams, people often:
  • Call the official Medicare helpline
  • Contact their State Health Insurance Assistance Program (SHIP)
  • Reach out to their state insurance department

Getting Started: Practical Next Steps

If you’re ready to explore your Medicare options, consider these steps:

1. Confirm your eligibility and key dates

   • Contact the Social Security Administration or the Railroad Retirement Board, if applicable.

2. Decide between Original Medicare and Medicare Advantage

   • Think about:
     • Your preferred doctors and hospitals
     • Your travel habits
     • Your budget and tolerance for variable costs
     • Your medication needs

3. Review prescription drug needs

   • Make a list of your current medications (names, dosages, how often you take them).
   • Use this list when comparing Part D or Medicare Advantage plans.

4. Gather key documents

   • ID and Social Security number
   • Proof of age and residency status if needed
   • Details about any current coverage (employer, union, VA, TRICARE, or others)
   • Income and asset information if you want to explore Medicaid, Medicare Savings Programs, or Extra Help

5. Contact official resources

   • The Social Security Administration for Parts A and B enrollment questions
   • The official Medicare helpline for coverage and plan questions
   • Your state Medicaid office for assistance programs
   • Your local State Health Insurance Assistance Program (SHIP) for free, unbiased counseling

By understanding what Medicare Parts A, B, C, and D do and how they fit together, you can approach those official channels with clearer questions and a better sense of what you need.