Medicare Parts A, B, C, and D Explained (2024)

Four Parts, One System — Built Over Six Decades

Medicare turned 61 in 2026. Signed into law in 1965 under President Lyndon Johnson, the program now covers 67 million Americans. What confuses most new enrollees is that "Medicare" is not a single insurance plan — it is four distinct programs that interact in specific ways. Part A covers hospitals. Part B covers outpatient care. Part C (Medicare Advantage) bundles A and B through private insurers. Part D covers prescription drugs. Understanding what each part actually covers — and what it costs in 2024 — determines whether your retirement health strategy works.

Medicare 2024 Cost Reference

Part A: Hospital Coverage and Its Gaps

Most people pay no Part A premium if they or their spouse worked at least 40 quarters (10 years) paying Medicare taxes. Those with 30–39 quarters paid $278/month in 2024; fewer than 30 quarters means $505/month. Premium-free Part A is one of the most valuable automatic benefits in American retirement planning — but its coverage has gaps that surprise beneficiaries.

Part A operates on a "benefit period" model, not an annual deductible. Each new hospital admission starts a benefit period. The $1,632 deductible applies per benefit period, not per year. Theoretically, a patient hospitalized three times in a year could owe three separate deductibles. Days 1–60 require only the deductible. Days 61–90 cost $408/day in coinsurance (2024). Beyond 90 days, beneficiaries tap lifetime reserve days — only 60 total — at $816/day. After reserve days are exhausted, Medicare pays nothing.

• Skilled nursing facility: covered fully for days 1–20; $204/day coinsurance days 21–100; nothing after day 100
• Home health care: covered if homebound and ordered by a physician
• Hospice: covered for terminal illness (six-month prognosis); regular Medicare services for that condition are waived
• Custodial (long-term) nursing home care: NOT covered — this is the most misunderstood gap in all of Medicare

Part B: The Monthly Premium You Always Pay

Part B is voluntary — but declining it without comparable employer coverage triggers permanent penalties. The 2024 standard premium of $174.70/month covers 25% of the program's costs; the federal government covers the remaining 75%. Higher earners pay more through Income-Related Monthly Adjustment Amounts (IRMAA). A single filer with income above $103,000 (or married above $206,000) paid a surcharge in 2024, with top-tier earners ($500,000+) paying $594/month total for Part B alone.

Part B covers physician visits, outpatient procedures, durable medical equipment, preventive services, and most cancer screenings. After the $240 annual deductible, Medicare pays 80% of approved amounts — leaving 20% coinsurance with no annual cap. A $100,000 hospital procedure could theoretically leave a beneficiary with $20,000 out of pocket from Part B alone, which is exactly why Medigap or Medicare Advantage exists.

Part C: Medicare Advantage's Promise and Constraints

Medicare Advantage plans are offered by private insurers approved by CMS. In 2024, 54% of Medicare beneficiaries enrolled in a Medicare Advantage plan — the first time the majority chose private coverage over traditional Medicare. Plans must cover everything original Medicare covers, and most add dental, vision, hearing, and fitness benefits that original Medicare never covers.

The tradeoff: networks. Medicare Advantage uses HMO or PPO models, meaning provider choice is restricted. Original Medicare is accepted by nearly every hospital and physician nationwide; Medicare Advantage networks vary dramatically by geography and insurer. Plans also use prior authorization for procedures more frequently than original Medicare.

Part D: Prescription Drug Coverage and the 2024 Redesign

The Inflation Reduction Act of 2022 restructured Part D significantly, with the most dramatic change taking effect in 2025: a $2,000 out-of-pocket cap on drug costs. In 2024, the old "donut hole" (coverage gap) was effectively closed, with beneficiaries paying 25% coinsurance through the coverage gap phase instead of the previous 47.5%–65% rates. The catastrophic threshold also dropped to $8,000 in total drug spending (2024).

Enrollment Windows and Late Penalties

The Part B penalty is permanent and compounds. A person who delays 24 months beyond their IEP without creditable coverage pays an extra 20% Part B premium for life. The Part D penalty is similarly permanent: 1% of the national base beneficiary premium multiplied by the number of months without creditable drug coverage. Both penalties are calculated annually and adjust with premium increases — they never disappear.

• Employer coverage at 65 qualifies as a Special Enrollment Period exemption — verify it counts as "creditable coverage" before delaying
• COBRA does not qualify as creditable coverage for avoiding Part D penalties in most cases
• Veterans Affairs (VA) drug coverage does qualify as creditable coverage for Part D purposes

Enrolling at the right time, in the right parts, with an eye on IRMAA thresholds and network access, is the foundation of a complete retirement health coverage plan.

This article is for informational purposes only and does not constitute financial advice.