By Marc Gilman
Questions? Call (800) 927-9326 or email
Key Takeaways
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Missing your enrollment window is the costliest mistake on this list, and the cost is permanent. The Part B late enrollment penalty adds 10% of the standard premium ($202.90/month in 2026) for every 12-month period you were eligible but didn’t enroll — for life, with no way to remove it except in rare appeal cases.
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The Part D penalty works the same way — 1% of the national base beneficiary premium ($38.99 in 2026) per month without creditable drug coverage, also permanent.
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COBRA and retiree coverage do not protect you from either penalty — only coverage tied to your or your spouse’s current, active employment does.
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Provider network mistakes look different depending on where you live — a plan’s network can technically include a provider that’s realistically inaccessible depending on your specific town, county, or commute.
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A Medigap plan doesn’t cover everything either — knowing exactly what gap it fills, and what it doesn’t, prevents its own category of surprise bills.
1. Skipping Preventive Care
Medicare covers an extensive list of preventive services — annual wellness visits, cancer screenings, cardiovascular screenings, diabetes screenings — often at no cost to you when criteria are met. Skipping these isn’t just a missed convenience; it’s the most reversible mistake on this list, since catching a condition early is almost always less expensive and less invasive than catching it late. Check the full list at Medicare.gov, since “preventive” covers more than most people assume.
2. Not Understanding Provider Networks
This mistake looks different depending on where you actually live, which is exactly why it trips people up. A plan’s directory might list a provider as in-network, but that doesn’t account for whether that provider is realistically accessible — a hospital system that serves one part of Massachusetts might not meaningfully overlap with a neighboring county, and a “nearby” specialist can mean a genuinely long drive depending on local traffic patterns. Confirm network participation and real-world accessibility before scheduling care, not just after.
3. Not Reviewing Medical Bills and Statements
Medicare Summary Notices (Original Medicare) and Explanations of Benefits (Medicare Advantage) show exactly what was billed and what Medicare paid. Billing errors happen more often than people expect — duplicate charges, incorrect codes, services billed that weren’t received. Reviewing these documents is the only way most people ever catch them, since providers and plans rarely flag their own errors.
4. Not Checking Prescription Drug Coverage Every Year
Part D formularies change annually, and a medication covered at a low tier this year can move to a higher tier — or off the formulary entirely — next year. This is exactly why the Annual Enrollment Period (October 15–December 7) exists: to let you re-shop before a formulary change quietly increases your out-of-pocket drug costs. Checking your preferred pharmacy’s status matters too, since preferred-pharmacy pricing can differ substantially from standard network pricing.
5. Missing Important Enrollment Periods
This is the mistake with the steepest, most permanent price tag. Miss your Initial Enrollment Period without qualifying employer coverage, and you’re looking at a 10% Part B penalty for every 12-month period you delayed — permanently. Someone who delayed five years, for example, would pay 50% more than the standard Part B premium for as long as they have Medicare. The Part D penalty follows the same permanent logic at a smaller scale.
Two details make this worse than people expect: COBRA and retiree coverage don’t protect you from these penalties — only current, active employment coverage does. And if you do qualify for a Special Enrollment Period, that window is 8 months from when your job or coverage ends, not indefinite.
State rules add another layer worth knowing. In Massachusetts, Medigap has an annual guaranteed-issue window every February 1–March 31, in addition to the one-time federal 6-month window. In New Hampshire, no such additional state window exists — the one 6-month opportunity is genuinely the only one you get.
6. Assuming All Services Are Covered
Original Medicare leaves real gaps — deductibles, coinsurance, and services that aren’t covered at all. Some of these gaps can be filled by a Medigap plan; others (like most dental, vision, and long-term custodial care) generally aren’t covered by either Original Medicare or a standard Medigap plan. Knowing which category a service falls into before you receive it is the only way to avoid a surprise bill after.
7. Not Using Benefits You’re Already Paying For
Many Medicare Advantage plans include extras — dental, vision, hearing, fitness memberships, over-the-counter allowances — that go unused simply because people don’t realize they’re already part of their plan. These aren’t hypothetical upsells; they’re benefits already included in your premium, which makes not using them a quiet form of leaving money on the table every single year.
8. Not Confirming Coverage Before Receiving Care
Some services are only covered under specific conditions — a particular diagnosis, a prior authorization, a specific provider type. Confirming coverage before an appointment, rather than assuming, is the difference between a routine visit and an unexpected bill weeks later.
9. Not Keeping Track of Healthcare Paperwork
Billing statements, coverage notices, and Explanation of Benefits documents are what make it possible to catch an error, file an appeal, or resolve a dispute. Without them, you’re reconstructing your own history from memory when a question comes up months later — which is a much harder position to argue from.
10. Waiting Too Long to Ask Questions
Medicare’s rules are genuinely complex, and the cost of waiting isn’t just stress — it’s often a missed deadline or a compounding misunderstanding. Asking early, before a decision needs to be made under pressure, is consistently cheaper than untangling a problem after the fact.
What To Do Next
Most of these mistakes share a common thread: they’re not about a lack of intelligence, they’re about not knowing which question to ask, or not having someone to ask it to before the deadline passes. The enrollment penalty numbers alone — a permanent 10% per year on Part B, permanent 1% per month on Part D — make this the one category where “I’ll figure it out later” is the most expensive option on the list.
If you want a second set of eyes on your coverage, your enrollment timeline, or a bill that doesn’t look right, reach out and we’ll work through it together.
Questions? Call (800) 927-9326 or email
