After years of working with seniors on their Medicare plans, I see the same five mistakes come up over and over. Each one is reversible — most of the time — but reversing them often costs money, time, or both. Read these before you make a decision. They're the ones that cost real people real dollars.
Mistake #1: Picking a Medicare Advantage plan based on TV ads
The celebrity-endorsed "free Medicare benefits" ads are designed to generate phone calls, not match you with the right plan. The plans featured in those ads are real plans — they're just not necessarily the right plans for your specific zip code, doctors, or prescriptions.
What I've seen: a senior signs up for the plan from the TV ad without checking the network. Six months later, they find out their primary care doctor isn't in-network. They're now stuck in the plan until the next Annual Enrollment window (October-December), and they're paying out-of-pocket for the doctor they've used for 15 years.
How to avoid it: never pick a plan based on a commercial. Always check (1) is my doctor in this network, (2) are my prescriptions covered at a reasonable tier, and (3) is the carrier's prior-authorization track record reasonable in my state.
Mistake #2: Not enrolling in Part D on time, thinking "I don't take any drugs"
The Part D late enrollment penalty is 1% of the national base premium per month you went without coverage, added to your premium permanently. Someone who skips Part D for 5 years owes a 60% premium surcharge for the rest of their life — even on the cheapest plan that's $20-30/month extra forever.
What I've seen: a healthy 65-year-old skips Part D because they take no prescriptions. They get diagnosed with diabetes at 70, finally enroll, and discover the penalty doubles their premium for the rest of their life.
How to avoid it: enroll in the cheapest Part D plan in your area during your Initial Enrollment Period, even if you take no medications. The lowest plans are typically $0-$10/month, and they prevent the permanent penalty.
Mistake #3: Missing the Medigap open enrollment window
The 6 months around your 65th birthday are the only time in most states when you can buy any Medicare Supplement plan with no health questions asked. After that, carriers can underwrite — meaning they can ask health questions and either charge more or refuse to sell you the policy at all.
What I've seen: a senior chooses Medicare Advantage at 65, gets diagnosed with a chronic condition at 68, decides they want to switch to a Supplement for more flexibility... and discovers no carrier will sell them one.
How to avoid it: at minimum, get a Supplement quote during your 6-month window. If you decide Advantage is right at the time, fine. But know that switching to a Supplement later may not be an option if your health changes. (Worth noting: Maine, Massachusetts, Connecticut, and New York have year-round guaranteed-issue rules. The other 46 states don't.)
Mistake #4: Picking a Part D plan based on the premium
This is the most common Part D mistake by far. People look at the monthly premium, pick the cheapest one, and end up paying $1,000+ extra per year in copays because their actual prescriptions are on bad tiers in that plan.
What I've seen: a senior on Eliquis ($500+/month brand-name drug) picks a $15/month Part D plan. The plan puts Eliquis on Tier 4 with a 33% coinsurance — $165/month for the drug. A plan with a $35/month premium would have Eliquis on Tier 3 at a $47 copay. They're paying $1,400 more per year by picking the "cheaper" plan.
How to avoid it: always run your actual drug list through every Part D plan in your zip code. Pick the plan with the lowest total annual cost (premium + deductible + expected copays), not the lowest premium.
Mistake #5: Not doing an annual Part D review
Part D plans change every year. The plan that was perfect for you last year may be terrible for you this year — formularies change, tier assignments change, premiums change. About a third of seniors I review during Annual Enrollment can save money by switching plans.
What I've seen: a long-time Part D client never switches plans, thinking "this works, why change?" One year, their plan moves their main medication from Tier 2 to Tier 4, doubling their annual cost. They never notice until they get the renewal letter — and by then they've already missed Annual Enrollment.
How to avoid it: every year during Annual Enrollment (October 15 - December 7), have someone review your plan against the new options. There's no fee for this review. It takes 30 minutes. It often saves real money.
The pattern behind all five
If you look at these mistakes together, the pattern is clear: making a Medicare decision without comparing alternatives. Every one of these mistakes comes from picking a plan in isolation, without checking what else was available.
Medicare has more choices than any other insurance product you'll ever buy. The benefit of all those choices is that there's almost always a plan that fits your specific situation. The cost is that the wrong plan is also always available. Independent comparison is the difference.