Original Medicare leaves 20% open ended
Original Medicare pays about 80% of the approved amount for Part B services and caps nothing. On a serious year that remaining 20% has no ceiling. Medicare Advantage and Medigap are two different ways of dealing with that, and you choose one path or the other rather than both.
Where they actually differ
Premium is the difference people notice first and it is the least important one. A $0 premium Medicare Advantage plan is not free: it trades the premium for cost sharing when you use care, and for a network.
| Medicare Advantage (Part C) | Medigap with Original Medicare | |
|---|---|---|
| How it works | Replaces how your Medicare benefits are delivered | Pays part of what Original Medicare leaves you |
| Monthly premium | Often low or $0, on top of your Part B premium | A real monthly premium, on top of your Part B premium |
| Doctors | Network, usually with referrals in an HMO | Any provider in the US who accepts Medicare |
| Out-of-pocket maximum | Yes, set by the plan each year | No cap needed: the policy covers the cost sharing it is designed to cover |
| Drug coverage | Usually built in | Separate Part D plan required |
| Extras such as dental or vision | Often included | Not included; bought separately |
| Can you be refused later? | No, enrollment is guaranteed in your area | Yes, outside your open enrollment or a guaranteed issue right |
Source: Medicare & You 2027 and Choosing a Medigap Policy, CMS
The door that closes
This is the asymmetry that matters and it is rarely explained at the point of sale. You can move from Medigap to Medicare Advantage essentially whenever an enrollment window is open. Moving the other way is conditional.
Outside your six-month Medigap open enrollment period, or a guaranteed issue right, a Florida insurer can ask health questions on a Medigap application and decline it. So choosing Medicare Advantage at 65 is a decision you can usually unwind only if your health later permits, or if something opens a guaranteed issue right for you.
A plan leaving Medicare is one of those guaranteed issue triggers. An Annual Notice of Change that simply makes your plan worse is not.
Which suits which situation
Neither is better in the abstract. Medicare Advantage tends to suit people who are comfortable inside a network, want the extras bundled and want a low premium. Medigap tends to suit people who travel, who want any Medicare provider without referrals, or who want budget certainty in a bad year.
The honest way to decide is to price both against your own doctors and prescriptions rather than against the monthly premium.
Frequently asked questions
Can I have both Medicare Advantage and Medigap?
No. Medigap only works alongside Original Medicare, and it is illegal for an insurer to sell you a Medigap policy while you are enrolled in a Medicare Advantage plan unless you are leaving that plan.
Is a $0 premium Medicare Advantage plan really free?
No. You still pay your Part B premium, and the plan recovers cost through copays, coinsurance and a network. A $0 premium describes the plan premium only, not what a year of care will cost you.
Can I switch from Medicare Advantage to Medigap later?
You can apply, but acceptance is not guaranteed outside your Medigap open enrollment period or a guaranteed issue situation. In Florida an insurer can use medical underwriting and refuse the application, which is why the timing of the original choice matters.
Does Medigap cover prescriptions?
No. Medigap policies sold today do not include drug coverage, so people with Original Medicare and Medigap add a standalone Part D plan. Medicare Advantage plans usually include drug coverage in the plan itself.
Sources
This guide explains officially published rules and figures. It is not an insurance quote and not an eligibility determination. Only HealthCare.gov, Medicare.gov, Social Security or the carrier can determine your eligibility and your actual price.
We do not offer every plan available in your area. Any information we provide is limited to those plans we do offer. Please contact Medicare.gov or 1-800-MEDICARE to get information on all of your options. Not connected with or endorsed by the U.S. government or the federal Medicare program.
Want this checked against your situation?
A guide explains the rules. Vivian checks what applies to you — your county, your doctors, your medications — in English or Spanish, at no cost to you.