Medicare is one of the most important financial decisions you will make in retirement — and one of the most unforgiving. Unlike most insurance, Medicare comes with hard deadlines, permanent penalties for missing them, and rules that interact with each other in ways that are easy to misread.

The good news: every mistake on this list is preventable. Here is what to watch for.

Mistake 1: Missing Your Initial Enrollment Window

When you turn 65, you have a seven-month window to enroll in Medicare: the three months before your birthday month, your birthday month itself, and the three months after. This is called your Initial Enrollment Period (IEP).

Miss it, and you face two consequences. First, you may have to wait until the next General Enrollment Period (January 1 – March 31 each year), with coverage not starting until July 1. That is a gap of months without Medicare coverage. Second, you will owe a late enrollment penalty on your Part B premium — 10% for every 12-month period you were eligible but did not enroll — and that penalty is permanent. It follows you for as long as you have Part B.

The exception: If you are still working at 65 and covered by a qualifying employer health plan, you can delay Medicare without penalty. The key word is "qualifying" — coverage through a small employer (fewer than 20 employees) does not qualify, and COBRA does not qualify. If you are unsure whether your employer coverage lets you delay, verify before your birthday month arrives.

Mistake 2: Skipping Part D Because You Do Not Take Prescriptions

Many healthy retirees look at their medication list, see nothing on it, and decide to skip Medicare Part D drug coverage. It feels like a reasonable way to save money. It usually is not.

If you go without creditable drug coverage for 63 or more consecutive days after your Initial Enrollment Period ends, you will owe a Part D late enrollment penalty when you do eventually sign up. The penalty is calculated as 1% of the national base beneficiary premium for every month you went without coverage — and like the Part B penalty, it is permanent.

More importantly, health changes quickly. A new diagnosis, a surgery, or a single expensive medication can turn a modest drug plan into an essential one overnight. Enrolling in a low-premium Part D plan at 65 — even if you take no medications — protects you from the penalty and ensures you have coverage when you need it.

Mistake 3: Assuming Medicare Covers Everything

Original Medicare (Parts A and B) is comprehensive for hospital and outpatient care, but it has meaningful limits that surprise many new enrollees:

• No out-of-pocket maximum. Under Original Medicare alone, your cost exposure is theoretically unlimited. The 20% Part B coinsurance has no ceiling.
• No routine dental, vision, or hearing coverage. These are not Medicare benefits. A dental emergency or hearing aids can cost thousands out of pocket.
• No long-term custodial care. Medicare covers skilled nursing care for a limited time after a qualifying hospital stay. It does not cover ongoing nursing home care or in-home personal care.
• Limited foreign travel coverage. Original Medicare generally does not cover care received outside the United States.

Understanding these gaps before you enroll — rather than after a claim is denied — lets you plan for supplemental coverage that fills them.

Mistake 4: Choosing a Plan Based on Premium Alone

The lowest monthly premium is not always the lowest total cost. This is one of the most common and costly errors in Medicare plan selection.

A Medicare Advantage plan with a $0 premium may look attractive compared to a Medicare Supplement plan with a $150 monthly premium. But the Advantage plan may carry a $7,550 annual out-of-pocket maximum, network restrictions, and prior authorization requirements. If you have a significant health event, the Supplement plan's higher premium may cost far less in total.

The right comparison is total annual cost — premiums plus expected out-of-pocket spending — not premium alone. That calculation requires knowing your health history, your medications, your preferred doctors, and the specific plans available in your zip code.

Mistake 5: Not Checking Whether Your Doctors Are In-Network

If you choose a Medicare Advantage plan, your coverage is tied to a provider network. Seeing a doctor outside that network — or in some plans, seeing a specialist without a referral — can result in significantly higher costs or no coverage at all.

Before enrolling in any Advantage plan, verify that your primary care physician, any specialists you see regularly, and your preferred hospital are all in-network for that specific plan in the current year. Networks change annually. A doctor who was in-network last year may not be this year.

This is less of a concern with Original Medicare paired with a Medigap plan, which covers any provider in the country who accepts Medicare — no network, no referrals required.

Mistake 6: Forgetting to Review Your Plan Every Year

Medicare plans are not set-and-forget. Every fall, during the Annual Enrollment Period (October 15 – December 7), you have the opportunity to review and change your Medicare Advantage or Part D plan for the following year.

Why does this matter? Because plans change. Premiums go up. Formularies — the list of covered drugs — are revised. Your medication may move to a higher cost tier, or be dropped from the formulary entirely. A plan that was the best fit at 65 may not be the best fit at 70.

Reviewing your plan each fall takes an hour or two. Ignoring it can cost hundreds of dollars in higher premiums or unexpected drug costs over the course of a year.

What to review each fall:

• Your plan's updated premium and out-of-pocket maximum
• Whether your current medications are still on the formulary at the same tier
• Whether your doctors are still in-network
• Whether lower-cost alternatives are available in your area

Mistake 7: Going It Alone Without Independent Advice

Medicare's rules are genuinely complex. The interaction between Part A, Part B, Part C (Advantage), Part D, Medigap, employer coverage, IRMAA, and enrollment periods creates a web of decisions that is easy to navigate incorrectly — especially the first time.

The most expensive mistake many retirees make is relying on a single source of information: a plan's own sales materials, a TV advertisement, or a friend's recommendation. Each of these has blind spots.

A captive agent works for one insurance company and can only show you that company's plans. A direct enrollment website may show you options but cannot explain the tradeoffs. A friend's experience reflects their health situation, not yours.

An independent Medicare broker works with multiple carriers, has no financial incentive to steer you toward any particular plan, and can compare your options side by side. Their services are free to you — brokers are compensated by the insurance carriers, not by the beneficiaries they serve.

The Bottom Line

Medicare mistakes are not just inconvenient — they can be expensive and, in some cases, permanent. A late enrollment penalty stays with you for life. A plan that does not cover your doctors or medications can disrupt care you depend on.

The best time to get informed is before you turn 65. The second-best time is right now.

James Hughes is an independent Medicare broker serving retirees across Missouri. He offers free, no-obligation consultations and works with multiple carriers to find the plan that fits your health needs and budget — not the plan that pays the highest commission.

Call 314-229-6146 or visit the Contact page to schedule your free Medicare review.