Turning 65 is one of the most significant financial and health milestones of your life, and the decisions you make in the months surrounding that birthday can shape what you pay for healthcare for the rest of your life. Medicare is not automatic for everyone, the enrollment windows are strict, and the penalties for missing them are permanent. Before you open a single mailer from an insurance company or sit through a single sales presentation, you need to understand the foundation: Original Medicare, how it works, what it costs, and what it doesn't cover.
Original Medicare is the federal health insurance program administered by the Centers for Medicare & Medicaid Services (CMS). It has two core parts. Part A covers inpatient hospital stays, skilled nursing facility care, hospice, and some home health services. Most people pay $0 in monthly premiums for Part A in 2025 if they or their spouse worked and paid Medicare taxes for at least 10 years (40 quarters). If you haven't met that work history threshold, Part A premiums can run up to $505 per month in 2025. Part B covers outpatient care — doctor visits, preventive services, lab work, durable medical equipment, and outpatient procedures. The standard Part B premium in 2025 is $185 per month, though higher-income beneficiaries pay more through what's called IRMAA (Income-Related Monthly Adjustment Amount), which can push that premium to over $628 per month for individuals earning above $500,000 annually.
The single most important date to understand is your Initial Enrollment Period, or IEP. This is a 7-month window: it begins 3 months before the month you turn 65, includes your birthday month, and extends 3 months after. If your birthday is in August, your IEP runs from May 1 through November 30. During this window, you can sign up for Part A and Part B without any penalty. If you delay enrolling in Part B beyond this window — and you don't have qualifying employer-based coverage — you'll face a permanent late enrollment penalty of 10% added to your Part B premium for every 12-month period you were eligible but didn't enroll. That penalty doesn't go away after a year or two. It stays with you for as long as you have Part B. The same logic applies to Part D prescription drug coverage: delay enrollment without creditable drug coverage from an employer or union plan, and you'll pay 1% of the national base beneficiary premium (about $36.78 in 2025) multiplied by the number of months you went without coverage — again, permanently added to your monthly premium.
If you're still working at 65 and covered by an employer group health plan through a company with 20 or more employees, you have more flexibility. In that situation, your employer coverage is considered primary, Medicare is secondary, and you can delay Part B enrollment without penalty. You'll receive a Special Enrollment Period (SEP) that lasts for 8 months after your employment or employer coverage ends — whichever comes first. However, if your employer has fewer than 20 employees, Medicare becomes your primary coverage at 65 regardless of whether you're still working, and you should enroll in Part B on time to avoid gaps and penalties. This distinction trips up a surprising number of people who assume their small-business employer plan protects them from the penalty clock.
Once you're enrolled in Original Medicare, you need to understand what it actually pays — because the gaps are significant. Medicare Part A comes with a hospital deductible of $1,676 per benefit period in 2025. Unlike most insurance deductibles that reset once a year, Medicare's benefit period resets each time you're admitted to a hospital and then go 60 consecutive days without inpatient care. That means if you're hospitalized twice in a year with less than 60 days between stays, you could owe that deductible twice. After 60 days in the hospital, you also begin paying daily coinsurance: $419 per day for days 61–90, and $838 per day for days 91 and beyond (using your 60 lifetime reserve days). Part B, meanwhile, requires you to meet a $257 annual deductible in 2025, after which Medicare pays 80% of approved costs and you pay the remaining 20% — with no out-of-pocket maximum. A serious illness or surgery could leave you with tens of thousands of dollars in 20% coinsurance with no cap.
This is precisely why most financial advisors and Medicare counselors recommend that beneficiaries who choose Original Medicare also purchase a Medicare Supplement Insurance policy, commonly called Medigap. These are standardized private insurance plans — labeled Plan A through Plan N — that help cover the cost-sharing gaps Original Medicare leaves behind. The most comprehensive option, Plan G (since Plan F is no longer available to new Medicare enrollees as of 2020), covers the Part A deductible, Part A coinsurance, Part B coinsurance, skilled nursing facility coinsurance, and foreign travel emergency care. In 2025, Plan G premiums vary widely by age, location, and insurer — ranging from roughly $100 to $300+ per month — but the predictability they provide can be worth the cost for people who use healthcare regularly. Plan N is a lower-premium alternative that still covers most gaps but requires copays of up to $20 for office visits and up to $50 for emergency room visits.
The alternative to Original Medicare plus Medigap is Medicare Advantage, also called Part C. These are private insurance plans approved by Medicare that bundle Parts A and B (and usually Part D) into a single plan, often with extra benefits like dental, vision, and hearing coverage that Original Medicare doesn't include. Medicare Advantage plans typically have lower monthly premiums — sometimes $0 beyond your Part B premium — but they use provider networks (HMOs or PPOs), require referrals in many cases, and have their own cost-sharing structures including copays and annual out-of-pocket maximums. In 2025, the maximum out-of-pocket limit for Medicare Advantage plans is $9,350 for in-network services. These plans can work well for people who are generally healthy, prefer lower upfront costs, and live in areas with robust plan networks. They tend to be less ideal for people with complex, chronic conditions who need frequent specialist access or who travel extensively.
One critical timing note for Medigap: when you first enroll in Part B, you have a 6-month Medigap Open Enrollment Period during which insurers cannot deny you coverage or charge you higher premiums based on your health history. This is your golden window. Once it closes, insurers in most states can use medical underwriting, meaning a pre-existing condition like diabetes, heart disease, or even a history of cancer could result in denial or significantly higher premiums. A handful of states offer additional protections — including birthday rule states like California, Oregon, Nevada, and New York, where you get a 30-day annual window to switch Medigap plans without underwriting — but in most of the country, your initial enrollment window is the best opportunity you'll ever have to lock in Medigap coverage at standard rates.
Before your 65th birthday, the most practical step you can take is to contact your State Health Insurance Assistance Program, known as SHIP. Every state has one, and it provides free, unbiased counseling from trained volunteers who have no financial stake in what plan you choose. They can walk you through your specific situation — your medications, your doctors, your budget — and help you compare real plan options in your area. You can find your local SHIP counselor at shiphelp.org. Medicare's own plan comparison tool at medicare.gov/plan-compare allows you to enter your prescriptions and see estimated annual costs across Part D and Medicare Advantage plans side by side. Use both resources before making any decisions, and be cautious of unsolicited calls or mailers that create urgency — legitimate Medicare enrollment doesn't require you to act within 24 hours.