If you're turning 65 this year, you're about to face one of the most expensive multiple-choice questions of your life.
The two paths look similar on paper, but the gap in what you'll actually pay can reach five figures over a few years.
Original Medicare (Parts A and B) covers hospital and doctor visits but leaves you exposed to deductibles, coinsurance, and no cap on annual out-of-pocket costs.
A Medicare Supplement plan, often called Medigap, plugs those holes.
You pay a monthly premium, and in exchange, most plans cover nearly all of that leftover cost.
These are private plans that replace Original Medicare.
Many advertise $0 premiums, dental, vision, and gym memberships.
The trade-off is networks, prior authorizations, and copays that show up every time you see a specialist or fill a prescription.
The premium math is where people get tripped up.
A Medigap Plan G might run $130 to $200 a month depending on your state and age, on top of the standard Part B premium ($185 in 2025).
But once you pay it, a hospital stay usually costs you almost nothing beyond a small deductible.
Your premium might be zero, but a three-day hospital stay could trigger hundreds in daily copays.
A course of chemotherapy or a skilled nursing stay can push your annual out-of-pocket maximum—up to $9,350 in-network in 2025—right to the edge.
There's another catch that rarely makes the brochure.
You can usually switch from Medicare Advantage to Medigap only during a narrow window.
After that, in most states, insurers can charge you more or deny you outright based on your health history.
Sign up for Advantage at 65, develop a condition at 70, and you may be locked out of the supplement you now need.
Agents earn bigger commissions on some Advantage plans, which is worth knowing when someone pushes one option hard.
The right answer depends on your doctors, your prescriptions, your travel plans, and how much risk you can absorb.
If you want predictable costs and freedom to see any provider who takes Medicare, a supplement often wins.
If you want the lowest possible monthly bill and can handle variable costs, Advantage can work.
Run your drug list through both plan types.
Then compare worst-case annual costs, not just the premium.
That single number tells the real story. **Our take:** The cheapest premium is not the same as the cheapest care.
For anyone with ongoing health issues or a desire to avoid surprise bills, the higher monthly cost of a supplement frequently pays for itself.
Final Thoughts
Run the worst-case math before you sign anything.