Medicare is complex — and the system is not designed to protect you from costly mistakes. Missing a deadline by one month can result in a permanent premium penalty. Choosing the wrong plan can expose you to tens of thousands in uncapped costs. Staying in a plan without reviewing it annually can cost you hundreds per year in unnecessary expenses.
These are the 10 mistakes I see most often — and how to avoid every one of them.
Mistake 1: Missing Your Initial Enrollment Period
Your Initial Enrollment Period (IEP) is a 7-month window around your 65th birthday. If you miss it without a qualifying reason (like having employer coverage), you face permanent late enrollment penalties: 10% added to your Part B premium for every 12-month period you were eligible but didn't enroll — for life.
The fix: Mark your calendar. Enroll during the 3 months before your birthday month for coverage to start on your birthday. Go to ssa.gov or call 1-800-MEDICARE.
Mistake 2: Not Enrolling in Part D Because You Don't Take Prescriptions
Many healthy seniors skip Part D because they don't take regular medications. Then they develop a condition requiring expensive drugs — and face a permanent Part D late enrollment penalty (1% of the national base premium per month without coverage) plus a coverage gap at the worst possible time.
The fix: Enroll in the cheapest available Part D plan in your area when you first become eligible. Many cost $7–$15/month and protect you from penalties while providing a safety net.
Mistake 3: Not Reviewing Your Part D Plan Every Year
Part D plans change their covered drug lists (formularies) every January. A drug that cost you $15 in December could cost $85 in January if it was moved to a higher tier — or dropped from the formulary entirely. Most people never notice until they're at the pharmacy.
The fix: Every October 15 – December 7, use Medicare.gov's Plan Finder to compare Part D plans using your current list of medications. Takes 15 minutes and can save hundreds per year.
Mistake 4: Choosing Medicare Advantage Based Solely on the $0 Premium
The $0 premium is the most effective marketing tool in healthcare. But Medicare Advantage plans make their money through cost-sharing when you actually use healthcare — copays, coinsurance, prior authorization, and out-of-pocket maximums up to $8,850 in-network. A serious illness can cost you far more than Medigap premiums would have.
The fix: Compare total potential out-of-pocket costs, not just premiums. For healthy people, Advantage may genuinely be cheaper. For people with complex conditions, Original Medicare + Medigap usually costs less overall.
Mistake 5: Missing the Medigap Open Enrollment Window
You have a one-time 6-month Medigap open enrollment window starting when you turn 65 and enroll in Part B. During this window, no insurer can deny you or charge you more based on health conditions. After it closes, most states allow medical underwriting — meaning you can be rejected or charged significantly more if you have any health conditions.
The fix: If you want Medigap, enroll during your open enrollment window. Don't wait to see if you'll need it.
Mistake 6: Assuming Medicare Covers Everything Abroad
Original Medicare provides almost no coverage outside the United States (with very limited exceptions near the Canadian and Mexican borders). Seniors who travel internationally and get sick can face enormous bills paid entirely out of pocket.
The fix: If you travel internationally, choose a Medigap plan (like Plan G or D) that includes foreign travel emergency coverage at 80% after a $250 deductible. Or buy travel health insurance for each trip.
Mistake 7: Not Checking if Your Doctors Accept Medicare
Not all doctors accept Medicare, and not all Medicare Advantage plans have the same networks. Some top specialists and cancer centers do not accept certain MA plans at all.
The fix: Before enrolling in any plan, verify that your key doctors — primary care, cardiologist, oncologist, or whoever you use most — are in-network for that specific plan.
Mistake 8: Ignoring Medicare Preventive Benefits
Medicare Part B covers dozens of free preventive services — Annual Wellness Visit, flu shots, colonoscopies, mammograms, bone density scans, depression screening, and more. Most seniors don't know what's covered and pay out of pocket unnecessarily or simply skip preventive care.
The fix: At your next doctor visit, ask for a Medicare Annual Wellness Visit — it's free, comprehensive, and can catch problems early.
Mistake 9: Not Applying for Extra Help With Drug Costs
Extra Help (the Low Income Subsidy) is a federal program that helps people with limited income pay for Part D costs — premiums, deductibles, and copays. It can save up to $5,300/year. An estimated 2 million eligible seniors are not enrolled.
The fix: Apply at SSA.gov or call 1-800-772-1213. Even if you think you earn too much, apply — the income and asset thresholds are more generous than most people expect.
Mistake 10: Not Appealing Medicare Claim Denials
Medicare and Medicare Advantage deny many claims that should be approved. The critical fact most seniors don't know: appeal rates are very low, but approval rates on appeals are very high. Studies show that over 40% of Medicare Advantage denials are overturned on appeal. Most people never appeal — they just pay the bill.
The fix: Always appeal a denial you believe is wrong. You have the right to appeal any Medicare coverage or payment decision. Your denial letter includes appeal instructions. Your State Health Insurance Assistance Program (SHIP) can help you for free.
Frequently Asked Questions
What is the most common Medicare mistake?
The most common and costly Medicare mistake is missing enrollment deadlines. Missing your Initial Enrollment Period without qualifying employer coverage results in a permanent 10% Part B premium penalty for every 12-month period you delayed — added to your premium for life.
What happens if you don't enroll in Medicare Part B on time?
If you miss your Medicare Part B enrollment window without qualifying employer coverage, you face a permanent late enrollment penalty: 10% added to your monthly premium for every full 12-month period you were eligible but didn't enroll. On a $174.70 monthly premium, that's an extra $17.47 per year — permanently.
Can Medicare Advantage deny claims?
Yes — Medicare Advantage plans can and do deny claims through prior authorization requirements. However, studies show that over 40% of Medicare Advantage claim denials are overturned on appeal. Always appeal a denial you believe is incorrect — your denial letter includes appeal instructions.
Should I enroll in Medicare Part D if I don't take any medications?
Yes — you should still enroll in the cheapest available Part D plan. If you skip Part D because you don't currently take medications and later develop a condition requiring expensive drugs, you will face a permanent late enrollment penalty plus a coverage gap at the worst possible time.
How often should I review my Medicare plan?
Every year during Annual Enrollment Period (October 15–December 7). Medicare plans change their drug formularies, provider networks, premiums, and copays every January. A plan that worked well last year may no longer cover your medications or your doctors. Reviewing annually can save hundreds of dollars.