Insurance

By the Retiree Report Editorial Team · Updated 2026-07-06 · 7 min read

This article is general information, not medical advice. Talk with a licensed clinician before making any decision about your care.

The Medigap 6-month open enrollment window: your one chance no insurer can deny

For six months, an insurance company selling Medicare supplement plans has to say yes to you. It can’t ask about your health, can’t turn you down for a bad back or a heart condition, and can’t charge you extra because of your medical history. That window opens once — the month you’re 65 or older and enrolled in Medicare Part B — and federal law does not give you a second one. Miss it, and in most states an insurer can put you through medical underwriting for the rest of your life.

What exactly is the Medigap open enrollment period?

Medigap, also called Medicare Supplement insurance, is a private policy that pays some of the costs Original Medicare leaves behind — deductibles, copays, the 20% coinsurance that has no ceiling on its own. You buy it from a private company, and companies normally get to decide who they’ll cover. The 6-month open enrollment period is the one stretch when that power is taken away from them.

According to Medicare.gov, the period starts on the first day of the month you’re both 65 or older and enrolled in Part B, and it runs for six months. During that time you can buy any Medigap policy any company in your state sells, at the same price a healthy person your age would pay. The insurer can’t refuse you, can’t rate you up for pre-existing conditions, and can’t stall your coverage — with one narrow exception covered below.

Here’s the part people miss: it’s one time only. AARP describes it as a “once-in-a-lifetime” window designated by federal law. Once those six months pass, the guarantee is gone.

When does the clock actually start?

The trigger is Part B, not your birthday. If you turn 65 but delay Part B because you’re still working and covered by a solid employer group plan, your Medigap window doesn’t start yet — it waits until you finally enroll in Part B. That’s by design, and it protects people who keep working past 65.

The timing matters if you want coverage the day Medicare begins. AARP suggests applying one to three months before your Part B coverage takes effect so the Medigap policy lines up with it. Do you have to wait until Part B is active to shop? No — you can apply in advance, but the six-month protected period itself is pinned to that Part B start date.

One caution. If you sign up for a Medicare Advantage plan when you first join Medicare instead of Original Medicare, you generally don’t use a Medigap window at all, because Medigap doesn’t work with Advantage. There’s a limited “trial right” if you try Advantage first and switch back within 12 months, but that’s a separate protection — not the same as your once-in-a-lifetime open enrollment. If you’re still weighing the two systems, our explainer on Medicare Advantage vs. Original Medicare walks through the trade-off.

What about pre-existing conditions during the window?

This is where the fine print earns a closer look. Buying during open enrollment stops an insurer from denying you or charging more, but a company can still impose a pre-existing condition waiting period of up to six months before it pays for care tied to a condition you had before the policy started. A pre-existing condition here means one a doctor treated or advised you about in the six months before your coverage began.

That waiting period sounds worse than it usually is, because “creditable coverage” wipes it out. KFF notes that insurers may impose up to a six-month wait — but if you had prior health coverage without a gap longer than 63 days, the insurer must subtract that time. The National Council on Aging puts it plainly: with six or more months of continuous prior coverage, the waiting period disappears entirely and your conditions are covered right away. Most employer plans, retiree coverage, COBRA, and Medicaid count.

So the reader who moves straight from a job’s health plan into Medicare at 65 typically faces no waiting period at all.

What happens if you miss the window?

Outside open enrollment, the rules flip. An insurer can require medical underwriting — a review of your health — and use it to deny you, delay you, or raise your premium. KFF lists conditions that routinely trigger a rejection, including cancer history, congestive heart failure, diabetes with complications, and stroke. In practice, one health event can lock you out of a better plan permanently.

There are escape hatches, but they’re specific. Federal “guaranteed issue” rights let you buy certain Medigap plans without underwriting after qualifying events — most often when you lose other coverage, when your Medigap insurer goes bankrupt, or during that 12-month Advantage trial period. You generally have 63 days from losing coverage to act. These rights are real, but narrow, and they don’t always give you access to every plan you’d want.

State law can be more generous. A handful of states — Connecticut, Massachusetts, Maine, and New York among them — require guaranteed issue on a continuing or annual basis, meaning residents there can switch without health screening well beyond the federal minimum, according to KFF. Roughly two-thirds of states also mandate some form of guaranteed issue tied to qualifying events. If you’re outside your window, call your State Health Insurance Assistance Program (SHIP) or state insurance department before you assume you’re stuck.

How to use your window well

Start by deciding which plan you want before the clock is running low, because switching later means underwriting. Plan G and Plan N are the two most popular choices for people newly eligible in 2026; our side-by-side on Plan G vs. Plan N compares the monthly premium against what you’d pay out of pocket. Then compare prices across companies — the same lettered plan (say, Plan G) covers identical benefits by law no matter who sells it, so a higher premium buys you nothing extra.

Use the plan comparison tool at Medicare.gov to see which insurers offer which plans in your ZIP code and what they charge, and if you want a human, a free SHIP counselor can review your options at no cost. One practical note: apply a month or two before your Part B start date so nothing lapses. This article is general information, not personalized insurance advice — a licensed agent or your SHIP office can confirm how the rules apply to your situation and state.

What to remember

The Medigap open enrollment period is a single six-month stretch, opening the month you’re 65 or older with Part B in force, when no insurer can deny you, screen your health, or surcharge you for past illness. That protection doesn’t renew, so treat it as a deadline, not a suggestion. If you’ve already missed it, don’t give up — federal guaranteed-issue rights and stronger state laws may still open a door, and a quick call to your state insurance department will tell you whether one applies to you.