Medicare Advantage vs. Medicare Supplement: The Actual Math

This is the fork in the road, and most of what is written about it is advocacy. People who sell one route describe the other as a trap.

Both are legitimate. They are different products with different failure modes, and the right answer depends on facts about you. Here is the comparison without a thumb on the scale.

What you are actually choosing between

Original Medicare — Parts A and B — pays for a lot but has no cap on what you can spend in a year. Part B generally leaves you responsible for 20% of costs, and 20% of an unbounded number is an unbounded number. That gap is the problem both routes solve.

Route one: Original Medicare plus a Medicare Supplement (Medigap) policy plus a standalone Part D drug plan. Three pieces. Higher monthly cost, very little at the point of care.

Route two: a Medicare Advantage plan. One plan, usually including drug coverage, that replaces how your Medicare benefits are delivered. Lower monthly cost, more paid as you go.

The premium comparison, honestly

Medicare Advantage plans often carry a low premium, sometimes zero, on top of your Part B premium. Medigap carries a real monthly premium, and a separate Part D premium on top of it. What that actually costs depends on your age, your ZIP code and the carrier, so it is a number to get quoted rather than to read in an article — but expect it to be the largest fixed difference between the two routes.

Over a year, that is a meaningful difference in fixed cost. It is not free money. You are buying two different distributions of risk.

Medigap

You pay a known amount every month. When you need care, you generally pay very little — with Plan G, after the annual Part B deductible, most Medicare-approved services are covered in full. Your spending is high, predictable, and essentially flat.

Medicare Advantage

You pay little or nothing monthly, then copays as you use care: a copay per specialist visit, per test, per day of a hospital stay. Your protection is the annual out-of-pocket maximum, which caps the total.

The comparison is not "cheap versus expensive." It is a known cost every month against a lower monthly cost with a much wider range of possible annual outcomes.

Networks

Medigap has no network. Any provider in the country who accepts Medicare accepts your coverage. No referrals, no prior authorization for the supplement, no service area. If you travel, split the year between two states, or want a specialist at a center of excellence, this is the practical difference and it is large.

Medicare Advantage is a network product with a service area. HMO plans generally require you to stay in network for anything but emergency and urgent care. PPO plans cover out-of-network care at higher cost sharing, but still generally only with providers who accept Medicare, and the cost difference can be substantial.

Networks also change annually, so a plan that covers your cardiologist this year may not next year.

Weighing these two against your own doctors and budget? Book a 15-minute call and we can run the numbers together.

Prior authorization

A real operational difference that rarely appears in a premium comparison: Medicare Advantage plans commonly require prior authorization for procedures, imaging, skilled nursing stays and some specialist care. That is a process with delays and denials, and an appeals path.

Original Medicare with a Medigap policy has far less of this. For someone managing a complex condition, that difference is worth real money in a way that does not show up in any premium column.

The underwriting window — the part that is hard to undo

This is the most consequential thing in this article, and the least known.

Your Medigap Open Enrollment Period is six months long. It begins the first month you are both 65 or older and enrolled in Part B. During those six months, carriers cannot use medical underwriting: they cannot decline you, cannot charge you more for your health history, and cannot impose waiting periods for pre-existing conditions.

It happens once. It does not repeat annually and it does not come back.

If you choose Medicare Advantage when you are first eligible, that six-month window opens and closes while you are enrolled in the Advantage plan. Later — say at 71, after a diagnosis — you may decide you want Original Medicare and a Medigap policy. At that point you are outside your open enrollment period, and unless a guaranteed issue right applies, the carrier can underwrite you. They can charge more. They can decline you outright.

The asymmetry is the whole point:

• Medigap to Medicare Advantage: available every fall during Annual Enrollment, no health questions.
• Medicare Advantage to Medigap: not guaranteed, and health questions apply.

There are limited exceptions, called trial rights. If you joined a Medicare Advantage plan when you were first eligible at 65 and decide within the first twelve months to switch to Original Medicare, you have a guaranteed issue right. There is a parallel right if you dropped a Medigap policy to try Medicare Advantage for the first time and disenroll within twelve months. Both are twelve months, generally one-time-only, and require you to apply within a narrow window — no more than 63 days after coverage ends.

Simply deciding you dislike your Advantage plan in year four is not a trial right. You can return to Original Medicare at Annual Enrollment, but Medigap will underwrite you.

Florida does not have a birthday rule, and does not have an annual guaranteed-issue window for Medicare Supplement. If you moved here from a state that does — California, Oregon, Illinois, Nevada and several others — that protection did not follow you.

So who should choose what

Lean Medigap if you travel or spend part of the year elsewhere, if you have a chronic or complex condition, if you want to choose specialists freely, if predictable costs matter more to you than a low premium, or if you simply want the decision made once.

Lean Medicare Advantage if the monthly premium is genuinely difficult, if your doctors are solidly in a good local network and you rarely leave the area, if the extra benefits are ones you will actually use, or if you value the simplicity of one plan and one card.

What should not drive it: a television commercial, what your neighbor chose, or a free meal.

What to do next

If you are approaching 65, do this before your Medigap window opens rather than after. It is the one deadline in Medicare that expires quietly and cannot be reopened.

Bring your doctor list, your prescription list, and an honest sense of how much variability in annual cost you can absorb. Let's spend fifteen minutes on it.