How Medigap timing works: the six-month window, and underwriting outside it

Medicare's fall dates are familiar because they repeat. The Annual Enrollment Period arrives every October, and a plan choice made this year can be revisited next year. Medicare Supplement insurance — Medigap — runs on its own clock, which is worth knowing simply because it works differently, not because anything about it is urgent.

What the window is

Under federal law there is a six-month Medigap Open Enrollment Period that begins the first month you have Medicare Part B and are 65 or older. During those six months, according to Medicare's own guidance, an insurance company can't refuse to sell you any Medigap policy it offers, can't charge you more because of pre-existing health problems, and can't make you wait for coverage to begin — apart from a limited wait that can apply to care related to a pre-existing condition.

How it relates to the fall dates

Under federal law this is a one-time period rather than an annual one, so it doesn't repeat the way the Medicare Open Enrollment Period does. The two are easy to conflate — both have "open enrollment" in the name — but the fall window is for Medicare Advantage and Part D plans, not for buying a Medigap policy.

Outside that period, the ordinary rule applies

After it closes, insurers in most states may use medical underwriting to decide whether to accept an application. Medicare describes the practical results plainly: a policy may cost more, fewer policy options may be available, and a company is allowed to decline an application that doesn't meet its underwriting requirements. That isn't a penalty for missing a deadline. It's the ordinary rule, and the six-month period is the carve-out from it.

Situations where health isn't a factor

There are defined circumstances in which a company can't turn you down. Medicare calls them guaranteed issue rights, or Medigap protections, and they generally arise when coverage you already had ends or changes through no decision of yours — plus certain trial situations for someone who tried Medicare Advantage and wants to move back. The list is specific and some of the rights carry time limits, so it's worth reading against your own circumstances rather than assuming one does or doesn't apply.

Two wrinkles

State law can be broader than federal law. Some states give people additional rights to buy a Medigap policy outside the federal window, which is why Medicare's guidance points readers to their State Insurance Department. Separately, for people who have Medicare under 65 because of a disability or ESRD, federal law generally doesn't require insurers to sell Medigap policies — though some states do provide for it.

The start date follows Part B

The window keys off Part B, not off your 65th birthday. Someone who delays Part B while covered by a current employer's plan also delays the Medigap window — it opens when Part B begins. Worth noting alongside the working-past-65 decision, since the two dates move together.

Nothing here forces a choice

Medigap is one route through Medicare; Medicare Advantage is another, and which fits depends on how you actually use care, what you're willing to pay monthly, and how you prefer your costs to be structured. The calendar only asks that you know which door you're looking at and how its timing works. If you'd like help mapping your own dates — when Part B starts, what the six months cover, whether a guaranteed issue situation applies — a licensed agent can walk through it with you, free and with no pressure.