What Is Medicare Supplement
Medicare Supplement insurance — Medigap — is private insurance that fills the cost gaps in Original Medicare (Part A and B): the 20% coinsurance, hospital deductibles, and coinsurance that would otherwise be uncapped.
| Question | Short Answer |
|---|---|
| What it is | Standardized plans (A–N) sold by private carriers |
| Works with | Original Medicare only — not Medicare Advantage |
| Core job | Covers Part A/B cost-sharing gaps |
| Standardization | Same benefits everywhere; only price differs |
| Regulator | State insurance departments + federal model rules |
The one-sentence mental model
Original Medicare pays its 80%; Medigap picks up the rest, up to everything for Plan G. The plan letters are federally standardized — a G is a G in every state — so shopping is purely about price and carrier quality (the carrier board), not benefits.
What Medigap is not
It is not Medicare Advantage (a replacement, not a supplement), not a drug plan (that is Part D — see prescriptions FAQ), and not dental/vision coverage. The MA comparison lives here: Medigap vs MA.
FAQ
Do I need Medigap if I have Original Medicare?
Without it, Part B’s 20% coinsurance is uncapped — one hospital stay and one bad diagnosis year can cost thousands; Medigap caps that exposure.
Who can buy Medigap?
People enrolled in Medicare A and B; most buy during the six-month OEP at 65.
Related reading: FAQ library · Plans board · OEP file