Medicare is the federal health insurance program serving over 65 million Americans. Despite its importance, the program's complexity leaves many eligible beneficiaries confused about what they're entitled to, when to enroll, and how to avoid costly gaps in coverage. Whether you're approaching 65, helping a parent navigate their options, or already enrolled and wondering if you're getting the most from your plan, this guide breaks down everything in plain language.
Who Is Eligible for Medicare
You automatically qualify for Medicare if you're a US citizen or permanent resident aged 65 or older who has paid Medicare taxes for at least 10 years (40 quarters) through employment. You're also eligible under 65 if you've received Social Security Disability Insurance (SSDI) for 24 months, have End-Stage Renal Disease (ESRD), or have Amyotrophic Lateral Sclerosis (ALS — enrollment begins immediately upon diagnosis).
If you or your spouse paid Medicare taxes for at least 10 years, Part A (hospital insurance) is premium-free. If you haven't met the 40-quarter threshold, you can still buy into Part A, but monthly premiums can reach $505 in 2026.
Understanding Medicare's Four Parts
Part A — Hospital Insurance
Covers inpatient hospital stays, skilled nursing facility care (up to 100 days following a qualifying hospital stay), hospice care, and some home health services. There's no monthly premium for most people, but you'll pay a deductible of $1,632 per benefit period in 2026. After 60 days in the hospital, daily coinsurance kicks in. Part A does NOT cover long-term nursing home care — this is the most common and costly misconception about Medicare.
Part B — Medical Insurance
Covers doctor visits, outpatient care, preventive services, durable medical equipment, and some home health care. The standard monthly premium is $185 in 2026 (higher for higher-income beneficiaries). After meeting the annual deductible ($257 in 2026), you typically pay 20% of the Medicare-approved amount for services. Part B covers many preventive screenings at no cost, including annual wellness visits, mammograms, colonoscopies, and flu shots.
Part C — Medicare Advantage
An alternative to Original Medicare (Parts A and B) offered by private insurance companies approved by Medicare. These plans must cover everything Original Medicare covers but often include additional benefits like dental, vision, hearing, and prescription drugs. Many Advantage plans have $0 monthly premiums beyond your Part B premium. The trade-off is that most Advantage plans use provider networks — you may need referrals and face out-of-network costs. In 2026, about 54% of Medicare beneficiaries are enrolled in Advantage plans.
Part D — Prescription Drug Coverage
Covers prescription medications through private plans approved by Medicare. Monthly premiums vary by plan (averaging $40-$55 in 2026). Each plan has a formulary listing covered drugs and their cost tiers. The Inflation Reduction Act capped annual out-of-pocket drug costs at $2,000 starting in 2025, eliminating the catastrophic coverage gap that previously left many seniors paying thousands for medications.
When and How to Enroll
Initial Enrollment Period (IEP): A 7-month window centered on your 65th birthday — starting 3 months before, including your birthday month, and extending 3 months after. Missing this window results in late enrollment penalties: Part B premiums increase by 10% for each 12-month period you were eligible but didn't enroll, and this penalty lasts for life.
Special Enrollment Period (SEP): If you're covered by employer insurance (through your own or spouse's current employment), you can delay Medicare enrollment without penalty. When that employer coverage ends, you get an 8-month SEP to sign up. COBRA coverage does NOT count as employer coverage for this purpose — a common and expensive mistake.
Annual Open Enrollment (October 15 - December 7): During this period, you can switch between Original Medicare and Medicare Advantage, change Advantage plans, or add/change Part D prescription drug plans. Changes take effect January 1.
Medigap (Medicare Supplement Insurance)
If you choose Original Medicare (Parts A and B), Medigap policies from private insurers can cover some or all of the out-of-pocket costs — deductibles, coinsurance, and copayments. Plans are standardized and labeled A through N. Plan G is the most popular in 2026, covering nearly all gaps except the Part B deductible. Your best opportunity to buy Medigap is during the 6-month Medigap Open Enrollment Period starting when you're both 65+ and enrolled in Part B. During this window, insurers cannot deny you coverage or charge more due to health conditions.
Common Costly Mistakes
Not enrolling on time: Late enrollment penalties for Part B are permanent. If you delay 2 years without qualifying coverage, you'll pay 20% more for Part B premiums for the rest of your life.
Assuming Medicare covers everything: Medicare doesn't cover dental, vision, hearing aids (under Original Medicare), long-term care, or most care outside the US. Plan accordingly with supplemental coverage.
Choosing plans based only on premiums: A $0-premium Advantage plan with a $7,500 out-of-pocket maximum could cost more than a plan with a $50 monthly premium and $3,000 maximum if you have significant health needs. Always compare total potential costs, not just premiums.
Not reviewing plans annually: Plan formularies, premiums, and provider networks change every year. What was the best plan last year might not be this year. Use Medicare's Plan Finder tool at Medicare.gov during Open Enrollment to compare options.
Getting Help
Free, unbiased counseling is available through the State Health Insurance Assistance Program (SHIP) in every state. SHIP counselors can explain your options, help you compare plans, and assist with enrollment — at no cost. Call 1-800-MEDICARE or visit Medicare.gov to find your local SHIP program.