For most people, turning 65 is the moment Medicare becomes real — and confusing. Suddenly you’re faced with Parts A, B, C, and D; enrollment windows; premium calculations; Medigap supplements; and a decision tree that seems designed to make your head spin. The good news: Medicare is a genuinely excellent program that provides comprehensive health coverage to over 65 million Americans. The key is understanding how the pieces fit together before your enrollment window opens. This guide gives you the foundational knowledge you need to make smart Medicare decisions.
What Is Medicare and Who Is Eligible?
Medicare is the federal health insurance program administered by the Centers for Medicare & Medicaid Services (CMS). It was established in 1965 under President Lyndon Johnson and initially covered only hospital and physician services. Today it provides comprehensive health coverage to:
- Americans age 65 and older
- People under 65 with certain disabilities who have received Social Security Disability Insurance (SSDI) for at least 24 months
- People of any age with End-Stage Renal Disease (ESRD) or ALS (Lou Gehrig’s disease)
You’re automatically eligible for Medicare at 65 if you or your spouse worked and paid Medicare taxes for at least 40 quarters (10 years). According to CMS, as of 2024 there were approximately 67 million Medicare beneficiaries in the United States, a number expected to grow to 80 million by 2030 as the Baby Boomer generation ages into eligibility.
The Four Parts of Medicare
Medicare Part A: Hospital Insurance
Part A covers inpatient hospital care, skilled nursing facility (SNF) care following a qualifying hospital stay, hospice care, and some home health services. For most people, Part A is premium-free — if you or your spouse worked and paid Medicare taxes for 40 or more quarters, your Part A premium is $0. If you have fewer than 40 quarters of Medicare-covered employment, you may pay up to $518/month (2025) for Part A.
Part A is not free in terms of cost-sharing. The Part A hospital deductible in 2025 is $1,676 per benefit period (not per year). After meeting the deductible, you pay nothing for the first 60 days of a hospital stay. Days 61-90 require a $419/day coinsurance payment. If you need more than 90 days of inpatient care, you can use “lifetime reserve days” (60 total over your lifetime) at $838/day.
Medicare Part B: Medical Insurance
Part B covers physician services, outpatient care, preventive services, lab tests, and medically necessary durable medical equipment. Unlike Part A, Part B requires a monthly premium. The standard Part B premium in 2025 is $185/month, though higher-income beneficiaries pay more through Income-Related Monthly Adjustment Amounts (IRMAA).
Part B has an annual deductible ($257 in 2025) and a 20% coinsurance for most covered services after the deductible is met. There is no out-of-pocket maximum under Original Medicare — meaning you could theoretically owe 20% of unlimited medical bills. This is why most beneficiaries pair Part B with either a Medicare Supplement (Medigap) plan or a Medicare Advantage plan.
Medicare Part C: Medicare Advantage
Medicare Advantage (MA) plans are private insurance plans approved by Medicare that provide all Part A and Part B benefits (and usually Part D drug coverage) through a single plan. MA plans often have lower premiums than Original Medicare plus a Medigap supplement, but use network restrictions (HMO and PPO structures) and may require prior authorization for certain services. We cover Medicare Advantage in depth in a separate article.
Medicare Part D: Prescription Drug Coverage
Part D is optional prescription drug coverage added to Original Medicare (or included in most Medicare Advantage plans). Part D plans are offered by private insurers and vary significantly in premiums, formularies (drug lists), and cost-sharing. The average basic Part D premium in 2025 is approximately $46.50/month, but premiums range widely.
When to Enroll: Critical Enrollment Windows
Medicare enrollment timing is one of the most consequential decisions you’ll make, and missing enrollment windows can result in permanent premium penalties. Here are the key enrollment periods:
Initial Enrollment Period (IEP)
Your IEP is a 7-month window centered on your 65th birthday month — it begins 3 months before your birthday month and ends 3 months after. During your IEP, you can enroll in Parts A, B, C, and D without penalty. Enrolling in the first 3 months of your IEP ensures coverage begins on the first day of your birthday month.
Special Enrollment Period (SEP)
If you or your spouse are still working at 65 and have employer-sponsored health coverage through an active employer (not COBRA), you can delay Medicare enrollment without penalty. When you lose that employer coverage (due to retirement or job loss), you have an 8-month Special Enrollment Period to sign up for Part B without penalty.
This is one of the most important nuances in Medicare: COBRA and retiree health coverage do NOT qualify you for a Special Enrollment Period. Once you retire and are on COBRA or retiree coverage, your 8-month SEP clock may already be running.
Late Enrollment Penalties
If you don’t enroll in Part B when first eligible and don’t qualify for a Special Enrollment Period, you’ll pay a permanent penalty of 10% of the standard Part B premium for each 12-month period you delayed. For Part D, the penalty is 1% of the national base beneficiary premium for each month you delayed, added to your premium permanently.
Original Medicare vs. Medicare Advantage: The Fundamental Choice
The most important Medicare decision for most people is choosing between Original Medicare (Parts A + B + optional D + optional Medigap) and Medicare Advantage (Part C). This decision shapes every aspect of your Medicare experience — your premiums, your cost-sharing, your network, and your ability to see the doctors you want.
Original Medicare is more flexible — you can see any doctor who accepts Medicare in the country, with no network restrictions and no referrals required. But it leaves significant out-of-pocket exposure that most people address with a Medigap supplement, which can add $100-$300/month in premium.
Medicare Advantage typically has lower or zero additional premiums but restricts you to a network of providers and often requires prior authorization for specialist visits, procedures, and high-cost medications. MA plans often include extras like dental, vision, hearing, and gym memberships that Original Medicare doesn’t cover.
What Medicare Doesn’t Cover
Medicare covers a great deal, but notable gaps exist. Original Medicare does not cover:
- Routine dental care (cleanings, fillings, extractions, dentures)
- Routine vision care (eye exams for glasses or contacts, glasses, contacts)
- Hearing aids and exams for fitting hearing aids
- Long-term custodial care (nursing home, assisted living)
- Most care outside the United States
- Cosmetic surgery
These gaps are why many Medicare beneficiaries purchase Medicare Advantage plans (which often include dental, vision, and hearing), Medigap supplements (which cover cost-sharing gaps), and standalone dental/vision plans.
Frequently Asked Questions
Do I need to enroll in Medicare if I have employer coverage at 65?
If you work for a company with 20 or more employees and are actively employed, you can delay Medicare without penalty. If your employer has fewer than 20 employees, Medicare becomes primary even if you have employer coverage — in that case, you should enroll in Medicare Parts A and B when first eligible.
Can I have Medicare and employer insurance at the same time?
Yes. When you have both, one plan is “primary” (pays first) and the other is “secondary” (pays what’s left). Which is primary depends on your employer size and whether you’re actively employed vs. retired.
When should I sign up for Part D if I don’t take prescriptions?
Even if you take no prescriptions today, enrolling in a low-cost Part D plan during your IEP is generally advisable to avoid the late enrollment penalty if you need drug coverage later. A basic Part D plan may cost as little as $5-$15/month.
What is IRMAA and will it affect me?
IRMAA (Income-Related Monthly Adjustment Amount) is an additional premium surcharge applied to Part B and Part D for beneficiaries with higher incomes. In 2025, individuals with modified adjusted gross income above $106,000 ($212,000 for married filing jointly) pay IRMAA surcharges. CMS bases IRMAA on your tax return from two years prior.
Navigating Medicare is complex, and the decisions you make at 65 can affect your coverage and costs for years to come. At Garden State Benefits, Paul Z Olah helps individuals and families in NJ and 25 other states understand their Medicare options and make informed enrollment decisions. Call 856-880-6340 or email paul@gardenstatebenefits.com — Paul answers the phone himself.