Medicare Part A, B, and D: What Each Part Actually Covers (and Who Pays What)

When you start researching Medicare for your parent, you quickly run into alphabet soup: Part A, Part B, Part D, Part C. Each letter covers something different, has different costs, and comes with its own rules about when your parent can sign up. Getting them confused is one of the most common mistakes adult children make — and those mistakes can result in late enrollment penalties or unexpected bills.

This guide breaks down exactly what Part A, B, and D cover, who qualifies for each, and what your parent will actually pay.

Medicare Part A: Hospital Insurance

Part A is what most people picture when they think of Medicare. It covers care in institutional settings — when your parent needs to be admitted somewhere rather than just seen in a clinic.

What Part A covers:

• Inpatient hospital stays (after a formal admission)
• Skilled nursing facility (SNF) care following a qualifying hospital stay of at least 3 days
• Hospice care for terminal illness
• Some home health care (after a qualifying hospital or SNF stay)

What Part A does NOT cover:

• Routine doctor visits or specialist appointments
• Outpatient procedures (these fall under Part B)
• Long-term custodial nursing home care (most nursing home care is not covered)
• Prescription drugs administered at home

Who Is Eligible for Medicare Part A

Your parent qualifies for Part A at age 65 if they (or their spouse) worked at least 10 years — 40 quarters — and paid Medicare payroll taxes during that time. For most American workers, this threshold has been met.

If they haven't met the 40-quarter requirement, they can still get Part A but will pay a premium — up to $518 per month in 2026. This situation is uncommon but worth checking for parents who spent many years outside the traditional workforce.

Premium-free Part A is automatic for most people who are already collecting Social Security when they turn 65. If your parent has not started Social Security yet, they need to actively enroll in Part A through SSA.gov.

What Part A Costs

Even with premium-free Part A, your parent will owe money when they use it. The Part A deductible in 2025 is $1,632 per "benefit period" — not per year. If your parent is discharged from the hospital and readmitted more than 60 days later, the deductible resets. After day 60 of a continuous hospital stay, daily coinsurance charges kick in ($408/day for days 61–90 in 2025).

This cost structure is why Medigap supplemental insurance is so important. Without it, a serious hospitalization can result in thousands of dollars in out-of-pocket costs.

Medicare Part B: Medical Insurance

Part B covers outpatient medical care — essentially anything your parent does with a doctor that doesn't require a hospital admission. It also covers certain home health services and durable medical equipment.

What Part B covers:

• Doctor visits (primary care and specialists)
• Outpatient procedures, surgeries, and lab tests
• Preventive services (annual wellness visit, cancer screenings, flu shots)
• Durable medical equipment like wheelchairs, walkers, and CPAP machines
• Mental health services (outpatient)
• Ambulance services
• Some home health care

What Part B does NOT cover:

• Prescription drugs taken at home (that's Part D)
• Routine dental, vision, or hearing care
• Long-term care or custodial care
• Cosmetic procedures

Eligibility and When to Enroll

Unlike Part A, Part B always has a monthly premium — $202.90 in 2026 for most beneficiaries. Higher-income parents pay more through Income-Related Monthly Adjustment Amounts (IRMAA), which can add hundreds of dollars per month.

The enrollment timing for Part B matters enormously. Most people sign up during their Initial Enrollment Period (IEP), the 7-month window centered on their 65th birthday month (3 months before, the birth month itself, and 3 months after).

If your parent is still working at 65 and has creditable employer coverage through a company with 20 or more employees, they can delay Part B without penalty. They then have an 8-month Special Enrollment Period to sign up after losing that coverage or leaving work.

If your parent misses their window without a valid reason to delay, they face a permanent Part B late enrollment penalty: 10% added to their monthly premium for every 12-month period they went without coverage. A 3-year delay means a 30% surcharge on their Part B premium for life.

The Difference Between Part A and Part B

The clearest way to think about it: Part A kicks in when your parent is admitted somewhere. Part B kicks in when your parent is seen by a doctor.

One area that trips families up is the observation status distinction. When a hospital places your parent "under observation" rather than formally admitting them, their stay is billed under Part B — not Part A. This matters because a Part B hospital stay does not count toward the 3-day qualifying stay needed to trigger Part A SNF coverage. Your parent could spend 4 days in the hospital under observation and still receive no SNF coverage for a subsequent rehab stay.

Medicare Part D: Prescription Drug Coverage

Part D covers prescription drugs your parent takes at home. It is run entirely by private insurance companies, though it is federally regulated and subsidized. Every Medicare beneficiary who wants drug coverage must enroll in a separate Part D plan (or choose a Medicare Advantage plan that bundles drug coverage).

What Part D covers:

• Most prescription medications, organized into tiers (generics are cheapest; specialty drugs are most expensive)
• Coverage varies by plan — each plan has its own formulary (drug list)

What Part D does NOT cover:

• Over-the-counter medications
• Vitamins and supplements
• Drugs administered in a hospital or doctor's office (those fall under Part A or B)

The $2,000 Out-of-Pocket Cap (New for 2025-2026)

The Inflation Reduction Act changed Part D significantly starting in 2025. The biggest change: there is now a hard cap of $2,000 per year on what your parent pays out of pocket for covered Part D drugs. In 2026, this cap rises to $2,100.

This eliminates the catastrophic drug costs that previously devastated seniors on expensive medications. If your parent takes high-cost specialty drugs — cancer treatments, multiple sclerosis medications, or biologics — this cap is life-changing.

The infamous "donut hole" coverage gap is also effectively gone under the new structure.

The Part D Late Enrollment Penalty

Like Part B, Part D has a permanent late enrollment penalty. If your parent goes more than 63 days without creditable drug coverage after becoming eligible, they owe 1% of the national base beneficiary premium ($38.99 in 2026) for every month they delayed — added to their Part D premium forever.

A 3-year delay would add about $14/month permanently. Over 20 years, that is more than $3,300 in extra premiums for the mistake of skipping coverage because "they don't take many medications right now."

How to Pick the Right Part D Plan

Never choose a Part D plan based on its monthly premium alone. The formulary — the specific list of drugs covered and what tier they are placed on — determines your parent's actual costs. A $10/month plan might charge $60 for a drug that a $45/month plan covers for free.

Use the Medicare Plan Finder at Medicare.gov and enter every medication your parent takes with the exact dosage and frequency. Sort results by "Lowest Drug + Premium Cost" to see the true total cost of care.

The Part B vs. Part D Distinction That Confuses Everyone

Some medications are covered by Part B rather than Part D, which surprises families. The rule of thumb: if a drug is administered by a healthcare provider (injected or infused in a medical setting), it is typically covered under Part B. If your parent picks it up at a pharmacy and takes it at home, it is Part D.

Common Part B drugs:

• Injectable osteoporosis drugs (like Prolia)
• Chemotherapy (when administered in a clinical setting)
• Insulin used with an insulin pump
• Certain eye injections (like Eylea for macular degeneration)

This distinction matters for comparing Medicare Advantage plans versus Original Medicare. Some Medicare Advantage plans have different cost-sharing structures for Part B drugs versus Part D drugs.

How the Parts Work Together

Here is the practical picture for a typical parent on Original Medicare:

• Part A covers hospitalizations and skilled nursing stays (with deductibles)
• Part B covers all outpatient care at 80% of the approved rate (your parent owes the remaining 20% with no annual cap — this is why Medigap exists)
• Part D covers prescription drugs taken at home (capped at $2,100/year out of pocket)
• Medigap (a separate private policy) fills in what Parts A and B leave uncovered

If your parent chooses Medicare Advantage (Part C), it replaces Parts A and B through a private insurer and usually bundles Part D drug coverage in one plan — but comes with network restrictions and prior authorization requirements.

What Adult Children Should Do Right Now

1. Confirm your parent's Part A status. Log into MyMedicare.gov or call 1-800-MEDICARE to verify they are enrolled and premium-free.
2. Check their Part B enrollment date. Make sure they are enrolled and understand when their 20% coinsurance exposure applies.
3. Review their Part D plan annually during October 15 – December 7 Open Enrollment. Formularies change every year — last year's best plan may be a poor choice this year.
4. Run the drug cost comparison on Medicare.gov before the Open Enrollment deadline, with their full current medication list.

Navigating Medicare for a parent involves more moving parts than most families expect. Our Medicare Enrollment Guide walks you through each decision — from choosing between Original Medicare and Medicare Advantage to picking the right Medigap plan and avoiding late enrollment penalties — with worksheets, timelines, and decision frameworks designed specifically for adult children managing this process. Get the Medicare Enrollment Guide to have a step-by-step roadmap in hand before your parent's next enrollment window opens.