Medicare Supplements (Medigap), explained

Why they exist

Original Medicare generally pays 80% of what Part B covers, and you pay the other 20%. There's no annual cap on your share.

Twenty per cent of a knee replacement is a real number. Twenty per cent of cancer treatment across a year is a much bigger one. Supplements exist to take that open-ended exposure off the table.

The thing that makes shopping simple

Supplement plans are labelled with letters — Plan G, Plan N, and so on — and the federal government defines what each letter covers. A company cannot sell you a Plan G with less in it.

That has a consequence worth sitting with: once you've decided which letter fits, the only remaining differences between companies are

• the price, which can vary a lot for identical coverage, and
• the company's history of raising rates, which matters more over twenty years than the price on day one.

I can show you both. Neither is something you should have to dig for.

What supplements don't do

• They don't cover prescriptions. You add a separate Part D plan.
• They don't add dental, vision, or hearing. Those are bought separately if you want them.
• They don't work with Medicare Advantage. Supplements pair with Original Medicare only; you can't have both.

The timing that decides everything

This is the part worth reading twice.

When you're 65 and enrolled in Part B, you get a six-month window in which a company must sell you any supplement it offers, at its standard price, regardless of your health.

After that window, in most states, the company can ask about your health history and turn you down. A condition you develop at 68 can close a door that was wide open at 65.

This window does not come round again each year. It's covered in more detail in the enrollment windows, and it's the single most common reason people call me too late.

How to think about which letter

Different letters trade a slightly lower premium against paying a small amount yourself when you use care. That's genuinely a preference question and not a right-answer question.

What I'd do is start from how you actually behave: if a bill arriving unexpectedly would bother you more than a slightly higher monthly cost, that points one way. If you'd rather keep the monthly number down and can absorb a modest amount when you use care, it points the other.