Understanding Medicare Supplement (Medigap) policies

Medigap policies are sold to work alongside Original Medicare, not Medicare Advantage. Here is what they do, how the lettered plans are structured, and an important limitation on when you can buy one without your health history being taken into account.

What Medigap is for

Original Medicare covers a large share of your medical costs, but it doesn't cover all of it. You're generally still responsible for deductibles and coinsurance on top of what Medicare pays, and Original Medicare has no annual limit on how much of that you could owe in a given year. A Medigap policy — sold by private insurers but standardized under federal rules — is built to help cover some or all of those gaps, so your out-of-pocket costs are more predictable. Medigap is sold specifically to pair with Original Medicare; it isn't something you carry alongside a Medicare Advantage plan.

Plans are standardized by letter

Medigap policies are sold under a set of standardized plan letters — Plan A, Plan B, Plan G, Plan N, and others — and, outside of a few states with their own standardization systems, a given letter covers the same set of benefits no matter which insurance company sells it. What differs between insurers offering the same letter is generally the price, not the coverage. This standardization is meant to make comparing policies more straightforward: once you understand what a given letter includes, you can compare insurers on cost and service rather than trying to decode different benefit structures from each one.

The limitation worth understanding: medical underwriting

This is the part of Medigap that catches people off guard, and it's worth understanding clearly before you count on being able to buy a policy whenever you want. You generally have a guaranteed-issue right to buy any Medigap policy sold in your state without medical underwriting during a specific window — most commonly the six months starting when you're 65 or older and first enrolled in Part B. Outside of that window, or outside of a small set of other situations that create a guaranteed-issue right, an insurer in most states is allowed to ask about your health history and can decline your application or charge you more based on it. That's a meaningful difference from Medicare Advantage and Part D, which generally can't turn you away for your health during an enrollment period you qualify for.

What Medigap doesn't include

A Medigap policy doesn't include prescription drug coverage. If you want drug coverage alongside Original Medicare and a Medigap policy, you'd add a separate, stand-alone Part D plan as a third piece of coverage. That's a different structure than Medicare Advantage, which is usually one bundled plan — Medigap is closer to building your own combination of Original Medicare, a supplement, and a drug plan, each with its own premium.

Whether Medigap is worth it for you depends on your health, your budget, and your timing — particularly whether you still qualify for guaranteed issue. It's worth having someone walk through your specific situation before you apply.