ANSWER FIRST: The five costliest: missing your Initial Enrollment Period, assuming employer coverage is always creditable, skipping Part D, choosing a plan without checking your doctors and drugs, and never reviewing the plan again. Each one is avoidable with a careful review before you enroll.

5 Costly Medicare Mistakes People Make at Age 65

Turning 65 is a milestone worth celebrating — but for millions of Americans, it also comes with a flood of Medicare mailers, confusing terminology, and decisions that feel impossible to make without a guide. Medicare has a lot of moving parts: Part A, Part B, Part C, Part D, Medigap supplements, enrollment windows, and income-based surcharges. It's easy to assume you'll sort it all out when the time comes.

That assumption is exactly where things go wrong.

Many people push Medicare decisions to the back burner, thinking they have more time than they do — or that their current coverage will carry them through without interruption. Others enroll in the first plan that arrives in the mail without comparing their options. Both approaches can lead to costly mistakes that follow you for years, and in some cases, for the rest of your life.

Medicare professionals see the same errors repeated constantly. The five mistakes covered in this article aren't rare edge cases — they're the most common missteps made by people who simply weren't aware of the rules before their 65th birthday arrived.

The stakes are real. Some late enrollment penalties are permanent, added to your premium every single month for as long as you have Medicare. A few wrong moves at 65 can mean paying hundreds of dollars more per year than your neighbor who made the same coverage choices but enrolled correctly. Understanding these mistakes now is the most valuable thing you can do before your birthday month arrives.

Quick Answer

The most costly Medicare mistakes at age 65 include missing your Initial Enrollment Period, skipping Part D drug coverage, and choosing a plan without fully understanding the out-of-pocket costs. These errors can result in permanent late enrollment penalties and unexpected medical bills that add up quickly. Knowing your deadlines and comparing Medicare Supplement plans before you enroll can save you thousands of dollars over time.

Why Medicare Decisions at 65 Deserve Your Full Attention

Age 65 isn't just a milestone birthday — it's the most important enrollment window of your entire Medicare journey, and it comes with a strict timeline that the federal government will not extend for most situations.

When you turn 65, you receive a 7-month Initial Enrollment Period (IEP) to sign up for Medicare. This window opens three months before your birth month, includes your birth month, and closes three months after. Missing it without a qualifying Special Enrollment Period means facing late penalties and gaps in coverage that could have been entirely avoided.

Beyond the IEP, there's another window that many people don't hear about until it's already closed: Medigap Open Enrollment. This 6-month period begins the month you turn 65 and are enrolled in Medicare Part B. During this window, insurance companies are required by law to sell you any Medicare Supplement plan they offer — at standard rates, without asking a single health question. This is called guaranteed issue.

Once that 6-month window closes, it's gone. If you want to switch to a Medigap plan later, insurers in most states can reject your application or charge you more based on your health history. This is the single best time to compare Medicare Supplement plans and lock in coverage.

The 2026 standard Part B premium is $185 per month. Understanding what that covers — and what it doesn't — is essential before choosing how to structure the rest of your Medicare coverage.

Mistake #1: Missing Your Initial Enrollment Period

What the Window Actually Looks Like

Your Initial Enrollment Period (IEP) is a 7-month window centered around your 65th birthday month. It opens 3 months before the month you turn 65 and closes 3 months after it. If your birthday is in June, for example, your window runs from March through September.

This isn't a soft deadline. Miss it without a qualifying reason — such as having creditable employer coverage — and you'll face permanent late enrollment penalties.

The Penalty That Never Goes Away

For Medicare Part B, the late enrollment penalty is 10% added to your monthly premium for every 12-month period you went without coverage. With the 2026 standard Part B premium sitting at $185 per month, a two-year delay means your premium could jump to $222 per month — and stay there for life.

That's an extra $444 per year, year after year, for simply not enrolling on time.

Many people assume they can wait because they're still working or because a spouse has coverage. That may or may not qualify as a valid exception. Before you assume you're covered, verify your situation with Medicare directly or speak with a licensed Medicare specialist.

Mistake #2: Skipping Part D Prescription Drug Coverage

Mistake #4: Choosing a Medicare Advantage Plan Based on a $0 Premium

A $0 monthly premium sounds like a great deal — and for some people, it genuinely works well. But many new Medicare enrollees choose a Medicare Advantage plan based on that headline number alone, without understanding what they could end up paying when they actually need care.

Here's the reality: Medicare Advantage plans can charge you out-of-pocket costs every time you use medical services. Doctor visits, specialist appointments, hospital stays, and procedures all come with their own copays and coinsurance amounts. In 2026, the out-of-pocket maximum for Medicare Advantage plans can reach up to $9,250 per year — and that's just for in-network care. Out-of-network costs can push that number even higher.

Beyond the cost issue, Medicare Advantage plans typically require you to use a specific network of doctors and hospitals. If your preferred physician isn't in the network, you may have to switch providers or pay significantly more to keep seeing them. Many plans also require prior authorizations — meaning your doctor has to get approval from the insurance company before certain treatments, tests, or procedures are covered. This can cause frustrating delays in care.

None of this means Medicare Advantage is the wrong choice for everyone. But it does mean you need to look well beyond the monthly premium before enrolling. Ask yourself: How often do I use medical care? Do my current doctors accept this plan? What would I actually pay if I had a serious illness or needed surgery?

For people who want more predictable costs and the freedom to see any doctor who accepts Medicare, a Medicare Supplement plan (Medigap) is often worth the monthly premium. Medigap plans help cover the gaps that Original Medicare leaves behind — like coinsurance, copays, and hospital costs — so you're not hit with large, unexpected bills.

Mistake #5: Setting It and Forgetting It

Once you're enrolled in Medicare, it's tempting to check the box and move on. But your coverage isn't something you should put on autopilot.

Medicare plans change every single year. A Medicare Advantage or Part D drug plan that was a strong fit in one year may look very different the next — with higher copays, a revised formulary (the list of covered drugs), or a narrower provider network. These changes take effect on January 1, and many people don't realize anything has shifted until they're already at the pharmacy or doctor's office.

Medicare's Annual Open Enrollment period runs from October 15 through December 7 each year. This is your opportunity to review your current coverage and make changes that take effect the following January 1. Use it.

If you have a Medicare Supplement plan, it's also smart to periodically check whether better rates are available. Medigap premiums vary significantly from one insurance company to another — even for the exact same standardized plan. Depending on your state and health status, you may be able to compare Medicare Supplement plans and switch to a lower-cost option with identical benefits. Taking an hour each fall to review your options could save you hundreds of dollars a year.

What You Should Do Next

If you're approaching 65 or recently enrolled in Medicare, here are clear action steps to protect yourself from these costly mistakes:

Enroll on time. Mark your Initial Enrollment Period on your calendar and sign up for Medicare Part B when you're first eligible — unless you have qualifying employer coverage. Missing this window means late enrollment penalties that last for life.
Explore your Medigap options early. Your six-month Medigap Open Enrollment window begins the month you turn 65 and enroll in Part B. During this window, you have guaranteed issue rights — insurers cannot deny you coverage or charge more based on your health. This window doesn't come back.
Compare Medicare Supplement plans before you commit. Premiums vary widely between insurance companies. Get quotes from multiple carriers so you're not overpaying for the same coverage.
Check your drug coverage every year. Review your Part D plan each fall during Open Enrollment to make sure your medications are still covered at a cost that makes sense for you.
Review all of your coverage annually. Set a reminder each October to look at your plan's updated documents and compare your options before the December 7 deadline.

Making informed decisions about Medicare doesn't have to be stressful. The key is knowing what questions to ask — and having the right resources to help you find honest, straightforward answers.

To compare Medicare Supplement rates from multiple insurance carriers in your area, visit medicaresavingschecks.com. It's a fast, simple way to see your options side by side. And if you're looking for free Medicare resources, guidance on your coverage choices, and tools to help you make confident decisions, SeniorResourceFinders.com is a trusted place to start. You've worked hard to get to this point — make sure your Medicare coverage works just as hard for you.

Have questions about your Medicare coverage? You can also fill out the contact form on MedSuppUSA.com and one of our licensed Kansas Medicare agents will reach out to help you compare your options - at no cost and with no obligation.