Medicare Guide 2025: Parts A, B, C & D, Enrollment Windows, Medigap & IRMAA

Medicare Parts A, B, C, and D: A Complete Breakdown

Medicare's four-part structure can be confusing because each part covers different services, has different premiums and cost-sharing, and requires separate enrollment decisions. Understanding each part's role is foundational to building a coherent healthcare strategy in retirement.

Part A (Hospital Insurance) is premium-free for anyone with at least 40 work quarters (10 years) of Medicare-covered employment, or whose spouse qualifies. It covers inpatient hospital stays, skilled nursing facility care following a qualifying hospital stay, hospice, and home health services. In 2026, the Part A deductible is $1,676 per benefit period (not per calendar year — a single hospitalization can trigger this multiple times). Hospital cost-sharing: $0 for days 1–60, $419/day for days 61–90, and $838/day for lifetime reserve days beyond 90. Long hospital stays can become very expensive without supplemental coverage.

Part B (Medical Insurance) covers outpatient services: doctor visits, specialist care, preventive services, durable medical equipment, mental health, and ambulance services. The 2026 standard premium is $185/month, but higher-income beneficiaries pay substantially more via IRMAA surcharges — up to $628/month at the highest bracket. The annual deductible is $257, after which Medicare pays 80% of approved costs. Critically, there is no out-of-pocket cap on the 20% coinsurance under Original Medicare alone — a $500,000 hospitalization leaves you responsible for $100,000. This is the primary reason Medigap supplemental coverage exists.

Part C (Medicare Advantage) is a private insurance alternative that replaces Original Medicare entirely. Plans must cover everything Parts A and B cover, but deliver it through managed care networks — typically HMO or PPO structures. Most plans also include Part D drug coverage and often add dental, vision, and hearing benefits not covered by Original Medicare. Part D (Prescription Drug) coverage is available either as a standalone plan added to Original Medicare, or bundled into a Medicare Advantage plan. Starting in 2025 under the Inflation Reduction Act, Part D out-of-pocket costs are capped at $2,000 per year.

Medicare Advantage vs Original Medicare + Medigap

The choice between Medicare Advantage and Original Medicare with Medigap supplemental insurance is one of the most consequential healthcare decisions you'll make — and unlike most financial decisions, it's difficult to reverse once made.

Medicare Advantage (Part C) advantages: Plans frequently offer $0 additional premium beyond what you already pay for Part B. Most include prescription drug coverage, eliminating the need for a separate Part D plan. They often include dental, vision, and hearing benefits that Original Medicare doesn't cover. All plans must include an annual out-of-pocket maximum, capping your worst-case cost in any given year.

Medicare Advantage disadvantages: HMO plans restrict you to in-network providers — accessing out-of-network care is either unavailable or far more expensive. PPO plans allow out-of-network access at higher cost-sharing. Prior authorization requirements mean the plan must approve many procedures before you receive them — creating friction for specialist referrals and some hospital admissions. Plans can exit markets annually, potentially disrupting your care relationships. Seriously ill patients who need frequent specialist access or treatment at major medical centers often find Advantage networks limiting.

Original Medicare + Medigap advantages: Any doctor or hospital that accepts Medicare in the United States — more than 95% of providers — will see you without network restrictions. There are no prior authorization requirements for medically necessary care. Out-of-pocket costs are highly predictable: Plan G (the most popular for new enrollees) covers everything except the Part B deductible ($257/year), eliminating the 20% coinsurance exposure entirely.

The critical Medigap enrollment trap: You have guaranteed-issue rights for Medigap — meaning no insurer can deny you coverage or charge you more based on health status — only during your initial 6-month enrollment window, which begins when you turn 65 and enroll in Part B. After that window closes, most states allow insurers to medically underwrite Medigap applications, meaning you can be denied coverage or charged substantially higher premiums if you have chronic conditions. This creates a practical lock-in: once you choose Medicare Advantage, switching to Original Medicare + Medigap later may be difficult or prohibitively expensive if your health has changed.

• →If you have frequent specialist needs or value provider freedom, Original Medicare + Plan G Medigap is generally superior
• →If you primarily see in-network doctors and want lower premiums with extra benefits, Medicare Advantage may fit well
• →The Medigap 6-month open enrollment window at 65 is a one-time opportunity — do not miss it if Original Medicare is your long-term preference
• →Compare Medigap premiums by plan letter via your State Health Insurance Assistance Program (SHIP) — the same standardized benefits can vary widely in cost by insurer

IRMAA: Income-Related Monthly Adjustment Amounts

IRMAA (Income-Related Monthly Adjustment Amount) is the mechanism by which Medicare charges higher-income beneficiaries more for their Part B and Part D coverage. For retirees doing Roth conversions, taking RMDs, or selling appreciated assets, understanding IRMAA's cliffs and the two-year lookback is essential for retirement income planning.

IRMAA is based on your Modified Adjusted Gross Income (MAGI) from two years prior — your 2026 Medicare premiums are determined by your 2024 tax return. This lookback creates planning opportunities: income-boosting events like Roth conversions or large asset sales in 2024 will affect Medicare costs in 2026, two years later. Conversely, retiring in 2024 with a large severance or sale proceeds may create unexpected IRMAA surcharges for two full years after retirement even as your ongoing income drops.

Life-changing event appeals: If your income drops significantly due to retirement, divorce, or the death of a spouse, you can file Form SSA-44 to request that Medicare use more recent income rather than the two-year-old tax return. This can immediately reduce IRMAA surcharges in the first years of retirement if you had high income in the prior two tax years.

The Roth conversion interaction: Roth conversions done at ages 63–64 will directly increase MAGI in those tax years, causing IRMAA surcharges at ages 65–66 — the first two years of Medicare. This is not a reason to avoid Roth conversions, but it should be factored into their cost. Conversely, Roth conversions done at 59–62 (before the IRMAA lookback window for initial Medicare eligibility) have no Medicare cost impact.

Medicare and Retirement Savings: The Strategic Interaction

Medicare planning and retirement account strategy interact in ways that create significant optimization opportunities — particularly around Health Savings Accounts, Roth conversion timing, and healthcare cost forecasting.

The HSA strategy for Medicare: Health Savings Accounts are the most tax-advantaged savings vehicle available to Americans — contributions are pre-tax (or tax-deductible), growth is tax-free, and qualified medical expense withdrawals are tax-free. The 2026 contribution limits are $4,300 for individual HDHP coverage, $8,550 for family coverage, with an additional $1,000 catch-up for those 55 and older. The optimal strategy for high earners with HSA access: contribute the maximum every eligible year, invest HSA funds in index funds for long-term growth, pay current medical expenses out-of-pocket when possible, and save all receipts. There is no time limit on HSA reimbursements — you can reimburse yourself years or decades later for expenses you paid out-of-pocket, making a large HSA balance available for tax-free withdrawals in retirement. Critically: you cannot contribute to an HSA after enrolling in Medicare, so the accumulation window closes at 65.

Healthcare cost projections: Fidelity's annual retiree healthcare cost study estimates that a couple retiring at 65 in 2026 will need approximately $315,000 in today's dollars to cover healthcare costs not paid by Medicare — premiums, cost-sharing, dental, vision, and hearing care. This does not include long-term care. Factoring this into your retirement number (rather than assuming Medicare covers everything) is essential for accurate financial planning.

The Original Medicare vs Advantage decision is effectively permanent from a cost perspective: if you start with Medicare Advantage and later want to switch to Original Medicare with comprehensive Medigap coverage, medical underwriting may make Medigap unaffordable or unavailable. The premium advantage of Medicare Advantage must be weighed against the switching cost risk if health deteriorates.

• →Maximize HSA contributions every eligible year and invest them for long-term growth — this creates a tax-free medical emergency fund
• →Save all medical receipts — HSA reimbursements have no time limit, enabling tax-free withdrawals decades later
• →Budget $315,000+ per couple for healthcare costs not covered by Medicare — a figure that dwarfs most retirees' healthcare assumptions
• →HSA contributions must stop when you enroll in Medicare — front-load contributions in the years before age 65

Long-Term Care: The Risk Medicare Doesn't Cover

Long-term care is the largest uninsured financial risk in retirement — and one of the most underappreciated. Medicare covers very limited skilled nursing care; it does not cover ongoing custodial care, which is what most people actually need as they age.

The statistics: According to the U.S. Department of Health and Human Services, 69% of Americans who reach age 65 will need some form of long-term care during their lifetime. The average care period is 2.5 years, but 20% of people need care for 5 or more years. Long-term care costs in 2026: nursing home private room averages approximately $130,000 per year; assisted living facility averages $60,000 per year; home health aide (44 hours/week) averages $65,000 per year; adult day services average $20,000 per year. A 3-year nursing home stay at private room rates could approach $400,000 — a catastrophic expense for most families.

What Medicare actually covers: Medicare Part A covers skilled nursing facility care only after a qualifying 3-day inpatient hospital stay, and only for skilled care (physical therapy, wound care, IV medications). Coverage is 100% for days 1–20, $200/day copay for days 21–100 (2026), and nothing after 100 days. Custodial care — help with daily activities like bathing, dressing, eating, and toileting — is explicitly excluded from Medicare coverage, regardless of setting.

Medicaid as the payer of last resort: Medicaid covers long-term care for those who have spent down their assets to the program's resource limits (typically $2,000 in countable assets for individuals in most states). Medicaid planning with a qualified elder law attorney can help married couples protect more assets through spousal impoverishment rules. However, Medicaid has a 5-year lookback period for asset transfers — assets given away within 5 years of applying for Medicaid can trigger ineligibility periods.

Planning options: Traditional long-term care insurance provides dedicated coverage for care costs, but premiums for a 60-year-old run $2,500–$4,000+ per year for a policy with a $150–$250/day benefit, 2–5 year benefit period, 90-day elimination period, and a CPI inflation rider (essential given how far premiums and care costs can rise). Hybrid life/LTC policies combine life insurance or annuity products with long-term care riders — unused LTC benefits pass to heirs as a death benefit, addressing the "I paid premiums for nothing" concern of traditional LTC insurance. Self-insuring is financially viable for those with $3M or more in liquid assets, who can absorb even worst-case care costs without financial impairment. Family caregiving reality: Research estimates the average family caregiver provides approximately $372,000 in unpaid care over the caregiving period — a figure that rarely appears in retirement plans but represents a real economic and personal cost to adult children and spouses.

• →69% of Americans will need long-term care — plan for it proactively rather than discovering the Medicare gap in crisis
• →Medicare covers skilled nursing only after hospitalization, for up to 100 days — it does not cover custodial care
• →Medicaid's 5-year lookback means LTC asset protection planning must start at least 5 years before care is needed
• →For assets below $3M, some form of LTC insurance (traditional or hybrid) is worth serious evaluation — consult a fee-only advisor or elder law attorney