Most coverage mistakes are recoverable at the next enrollment window. A few are not. The difference is worth knowing before you act, not after.
Permanent, or close to it
1. Delaying Part B when your employer plan pays second
If your employer is below the size threshold, Medicare is the primary payer whether or not you enrolled. Claims processed on the assumption that Medicare already paid its share can leave you owing the difference, applied backwards over months.
A late-enrollment penalty for Part B can also attach and, unlike some penalties, generally stays for as long as you have Part B.
Before you delay: get written confirmation from your employer plan administrator that the coverage is creditable and pays primary.
2. Letting a Medicare Supplement go and expecting to return
There is a period when you first become eligible during which a Supplement must be issued regardless of your health. Outside it, and outside a narrow set of guaranteed-issue situations, an insurer may apply medical underwriting — and may decline.
This is why choosing between Original Medicare with a Supplement and Medicare Advantage is worth doing deliberately at the start. Moving one way is usually straightforward. Moving back, years later and after a diagnosis, may not be available.
3. Going without creditable drug coverage
A late-enrollment penalty for Part D can attach and generally persists. “Creditable” is the operative word — some employer and union coverage counts, some does not, and the plan is required to tell you which in an annual notice. Keep it.
Hard to reverse
4. Cancelling before the replacement is confirmed
Cancel first and you can create a gap that no window will let you close. Enrolling in a replacement usually ends the old plan automatically; manual cancellation is rarely necessary and frequently harmful.
The order is: confirm the new plan, check network and formulary, get the start date in writing, and only then deal with the old plan.
5. Missing a Special Enrollment Period
The clock generally runs from the qualifying event, not from when you noticed. Miss it and you may wait until the next annual window with no coverage in between.
If you know an event is coming — a retirement date, a job ending — start before it happens.
6. Guessing high on a Marketplace income estimate
Advance premium credits are reconciled against actual income at tax time. Estimate low and earn more, and some of it comes back. It is arithmetic rather than a penalty, but it arrives more than a year later, long after anyone remembers the conversation.
Update the estimate during the year when circumstances change.
Fixable
7. Choosing on monthly cost alone
The commonest mistake and the least damaging, because it usually corrects at the next window. You pay more than you needed to for a year, and you switch.
The exception is when it costs you a doctor mid-treatment. Then it stops being fixable.
The pattern underneath all seven
Six of these seven are timing errors rather than judgement errors. The person understood the options; they acted in the wrong order or in the wrong month.
Which is genuinely good news, because timing is the easiest thing to get help with. A single phone call before you act — to us, to 1-800-MEDICARE, or to a free SHIP counsellor — catches nearly all of them.
And one that is not on this list
Being talked into a plan you did not want by someone paid to sell it. We are paid by commission, which means an incentive exists, and we would rather you knew that than guessed at it.
If a free route through Medicare.gov or HealthCare.gov suits you better, that is what we will tell you. If we would not, this page would not exist.
Where to check this independently
Nothing on this page is advice about your situation, and none of it replaces the free sources. The Medicare Plan Finder,1-800-MEDICARE, your SHIP counsellor andHealthCare.gov are free, independent, and show plans we cannot sell.
Healthbase is a licensed insurance agency, not a government agency and not connected with Medicare or any federal or state program.