Three months before your 65th birthday, your mailbox turns into a war zone. Insurance companies buy lists of people approaching Medicare age and carpet-bomb them with envelopes designed to look official. Somewhere underneath that pile is a real decision with real deadlines, and getting it wrong can cost you a penalty that lasts the rest of your life.
Here is the whole system, stripped of the sales pitch.
The four parts, in plain English
Part A: hospital insurance
Part A covers inpatient hospital stays, skilled nursing facility care after a qualifying hospital stay, hospice, and some home health care. Most people pay no monthly premium for Part A because they (or a spouse) paid Medicare taxes for at least 10 years of work. That is the "free" part of Medicare you have heard about.
Free does not mean cost-free. Part A carries a deductible per benefit period, not per year. For 2026 that deductible is a little over $1,700, and it can hit you more than once in a single year if your hospital stays are spaced far enough apart. Verify the current figure at medicare.gov.
Part B: medical insurance
Part B covers doctor visits, outpatient care, lab work, durable medical equipment, and preventive services. Unlike Part A, almost everyone pays a monthly premium for it. The standard Part B premium for 2026 is $202.90 a month, and higher-income households pay more through an income-related surcharge called IRMAA. After a modest annual deductible, Part B generally pays 80 percent of approved charges and you pay 20 percent, with no cap on that 20 percent under Original Medicare. Read that sentence again, because it drives most of the other decisions you will make.
Part C: Medicare Advantage
Part C is not extra coverage on top of Medicare. It is a replacement delivery system: a private insurance plan that bundles Parts A and B (and usually D) into one product, often with dental, vision, or gym extras bolted on. Many Advantage plans charge little or no premium beyond your Part B premium. The trade-offs are provider networks, prior-authorization requirements, and cost-sharing structures that differ from Original Medicare. Neither option is automatically better; they are different bets on your future health.
Part D: prescription drug coverage
Part D is drug coverage sold by private insurers, either as a standalone plan alongside Original Medicare or built into an Advantage plan. Since 2025, Part D has an annual out-of-pocket cap; for 2026 the cap is $2,100, after which your covered drugs cost you nothing for the rest of the year. That cap fixed the old "donut hole" problem that used to bankrupt people on expensive medications.
What it costs in 2026, roughly
- Part A: $0 premium for most people; deductible just over $1,700 per benefit period.
- Part B: $202.90 standard monthly premium; annual deductible around $280; then 20 percent coinsurance.
- Part C: varies by plan and county, from $0 premiums up.
- Part D: premiums vary widely by plan; maximum deductible $615; annual out-of-pocket cap $2,100.
These numbers reset every year. Treat anything printed on paper, including this article, as a starting point and confirm the current figures on medicare.gov before you make decisions.
The enrollment windows that actually matter
Initial Enrollment Period (IEP)
Your personal seven-month window: the three months before your 65th birthday month, your birthday month, and the three months after. Enroll in the early months and coverage can start the month you turn 65. If you are already receiving Social Security benefits, you are enrolled in Parts A and B automatically and a card shows up in the mail. Everyone else has to act, and you do it through Social Security, not Medicare: online at ssa.gov, by phone at 1-800-772-1213, or at a local office.
Special Enrollment Periods (SEP)
Still working at 65 with employer coverage from a company with 20 or more employees? You can usually delay Part B without penalty and enroll later through a Special Enrollment Period that runs for eight months after the employment or the coverage ends, whichever comes first. Two traps hide here. First, COBRA does not count as employer coverage for this purpose, a detail that catches thousands of people every year. Second, if your employer has fewer than 20 employees, Medicare is generally supposed to pay first and you likely need Part B at 65 even if you keep the group plan. Confirm your situation with your benefits administrator in writing.
General Enrollment Period and annual windows
Miss your IEP with no SEP to save you, and you wait for the General Enrollment Period, January 1 through March 31, with coverage starting the month after you sign up. Separately, every fall brings Medicare Open Enrollment, October 15 through December 7, when anyone already on Medicare can switch Advantage plans, change drug plans, or move between Original Medicare and Advantage for the following year. There is also a Medicare Advantage Open Enrollment Period from January 1 to March 31 for people already in an Advantage plan who want one do-over.
The late penalties, or why deadlines are not suggestions
The Part B late enrollment penalty adds 10 percent to your premium for each full 12-month period you were eligible but not enrolled, and you pay it for as long as you have Part B. Skip Part B for three years without qualifying coverage and your premium is 30 percent higher, permanently.
The Part D penalty is subtler: 1 percent of the national base premium (about $39 in 2026) for each month you went without drug coverage or other creditable coverage after becoming eligible. It sounds small. It compounds into real money over a 20-year retirement, and it also never goes away. Our advice, after reading more of these penalty-reconsideration cases than we care to admit: even if you take no medications today, enroll in the cheapest Part D plan in your area rather than going bare. It is penalty insurance that often costs less than a streaming subscription.
Original Medicare or Advantage: the actual decision
Original Medicare (A plus B, usually with a standalone Part D plan) lets you see any provider in the country who accepts Medicare, no referrals, no networks. Its weakness is that unlimited 20 percent coinsurance, which is why many people add a Medigap supplement policy to cap their exposure. Critically, your one guaranteed window to buy Medigap without medical underwriting is the six months after your Part B starts. Miss it, develop a health condition, and insurers in most states can decline you or charge you more later.
Medicare Advantage caps your annual out-of-pocket costs and often costs less month to month, in exchange for networks and prior authorization. It can be a fine deal for healthy people who travel little and whose doctors are in-network. The comparison tool at Medicare Plan Finder shows every Advantage and drug plan in your ZIP code with estimated annual costs based on your actual medication list. Spend an hour there before you believe any television commercial.
Whichever direction you lean, it helps to understand how Medicare fits alongside other coverage types; our overview of health insurance options in 2026 walks through the broader system.
If the premiums are a stretch
If your income is limited, two programs can dramatically change the math. Medicare Savings Programs, run by state Medicaid agencies, can pay your Part B premium and sometimes your deductibles and coinsurance too. And Extra Help, the federal Part D low-income subsidy, caps your prescription copays at a few dollars each. Neither is automatic for most people; you have to apply, and huge numbers of eligible seniors never do.
The surcharge nobody warns you about: IRMAA
If your modified adjusted gross income from two years ago exceeded certain thresholds — for 2026, the surcharge brackets begin a bit above $100,000 for a single filer and twice that for joint filers — you pay an income-related monthly adjustment amount on top of the standard Part B and Part D premiums. Two years ago is the operative phrase: your 2026 premium is based on your 2024 tax return. This ambushes new retirees constantly, because the year you retire, Social Security is still looking at a tax return from your peak earning years. There is a fix. If your income dropped because of a life-changing event — retirement, a spouse's death, divorce — you can file Form SSA-44 asking Social Security to use your current, lower income instead. It is a two-page form, it works, and most people subject to IRMAA in their first retirement year have never heard of it.
Mistakes that generate the most regret
- Assuming COBRA protects you. It does not count as employer coverage for delaying Part B. People discover this when the penalty letter arrives.
- Contributing to an HSA after enrolling. Once any part of Medicare starts, HSA contributions must stop — and Part A can be backdated up to six months when you enroll late, which can retroactively disqualify contributions you already made.
- Choosing an Advantage plan without checking the drug formulary. The medical network can be perfect while your one expensive medication sits on a punishing tier.
- Letting a plan auto-renew for years. Networks, formularies, and premiums shift annually; the plan you chose at 65 may be a poor fit at 72.
Your one-hour starter plan
- Mark your seven-month Initial Enrollment Period on a calendar right now, even if 65 is a year away.
- If you are still working, get a written answer on whether your employer coverage lets you delay Part B safely.
- List every prescription you take, then run the Plan Finder comparison with that list.
- Decide on Original Medicare plus Medigap versus Advantage before your Medigap guaranteed-issue window closes, not after.
- Recycle the marketing mail. Every legitimate fact in it lives at medicare.gov or ssa.gov, minus the sales agent.
The system is more bureaucratic than it needs to be, but it is learnable in an afternoon, and the deadlines are the only part that can genuinely hurt you. Handle those first and the rest is comparison shopping.
