Montana Medicare Supplement Guide: Open Enrollment, Under 65 (2026)

A Montana Medicare Supplement policy can be bought without medical underwriting during a six-month window that opens once you're 65 and enrolled in Medicare Part B.1 The Montana Commissioner of Securities and Insurance (CSI) regulates all Medigap (Medicare Supplement) insurance sold in Montana, and CSI's Medicare FAQ says Montana open enrollment lasts six months beginning on the first day of the month a person is 65 and enrolled in Medicare Part B.1 Montana also appears on the Centers for Medicare & Medicaid Services (CMS) list of states that require insurance companies to offer at least one kind of Medigap policy to people with Medicare under 65.1

In This Guide

• When Is the Montana Medigap Open Enrollment Window?
• Will a Montana Medicare Supplement Policy Cover a Pre-Existing Condition Right Away?
• Can You Buy a Medicare Supplement Policy Under 65 in Montana?
• What If Your Medigap Company Leaves Montana or Goes Bankrupt?
• Which Medicare Supplement Plans Can You Buy in Montana?
• Should You Pick Medigap or Medicare Advantage?
• What Does Montana Law Protect After You Buy?
• Montana Medigap Rules at a Glance
• Who Can Help With Medigap Questions in Montana?
• Frequently Asked Questions
• Learn More

When Is the Montana Medigap Open Enrollment Window?

The Montana Commissioner of Securities and Insurance answers the timing question directly: "Open enrollment lasts for 6 months beginning on the first day of the month when the individual is 65 years of age and enrolled in Medicare Part B."1 Medicare's guide Choosing a Medigap Policy describes the same six-month Medigap Open Enrollment Period as starting the first month you have Part B and you're 65 or older.1

During the six-month Medigap Open Enrollment Period, Medicare's guide says an insurance company:

• can't refuse to sell you any of the Medigap policies it offers;
• can't use medical underwriting to decide whether to accept your application, or deny you coverage because of pre-existing health problems;
• can't charge you more for a Medigap policy because you have health problems.1

Federal statute sets that floor for every state, Montana included. Section 1882 of the Social Security Act, at subsection (s)(2)(A), bars a Medicare supplemental policy issuer from denying, conditioning or pricing a policy on health status, claims experience or medical condition when the application is submitted before or during the six-month period that begins the first month a person is 65 or older and enrolled in Part B.2

The Medigap Open Enrollment Period happens once. Medicare's guide calls it a one-time enrollment period that doesn't repeat every year, and says that outside it there's no guarantee an insurance company will sell you a Medigap policy if you don't meet its medical underwriting requirements, unless you have a guaranteed issue right.1 Medicare.gov adds that outside the window you may pay more for a Medigap policy and have fewer policy options, though you may have additional rights under state law.2 Brevy's national guide to the Medigap open enrollment period covers the federal timing in more depth.

Will a Montana Medicare Supplement Policy Cover a Pre-Existing Condition Right Away?

A guaranteed sale is not always immediate coverage for every condition, and Montana statute sets the outer limit. Montana Code Annotated (MCA) 33-22-904(4) provides that a Medicare Supplement policy or certificate may not exclude or limit benefits for losses incurred more than 6 months from the effective date of coverage because the loss involved a preexisting condition.1

MCA 33-22-904(4) also limits what a Montana Medicare Supplement policy can call a preexisting condition: the policy may not define it more restrictively than a condition for which a physician gave medical advice, or recommended or provided treatment, within 6 months before the coverage's effective date.1

Brevy's guide to Medigap and pre-existing conditions explains how the federal waiting-period rules work alongside state law.

Can You Buy a Medicare Supplement Policy Under 65 in Montana?

Montana is one of the states where the answer can be yes. Medicare's Choosing a Medigap Policy guide (March 2026) lists Montana among the states that, at the time the guide was printed, require insurance companies to offer at least one kind of Medigap policy to people with Medicare under 65.1

That Montana listing is an exception to the federal baseline. Medicare's guide states that federal law generally doesn't require insurance companies to sell Medigap policies to people who are under 65.1 The same CMS guide notes that states differ in whom they cover: some give these rights to all people with Medicare under 65, while others extend them only to people eligible for Medicare because of disability or End-Stage Renal Disease (ESRD).1 Ask CSI which under-65 buyers the Montana requirement reaches before you rely on it.

CSI's own Medicare FAQ takes up the question from someone under 65 who has Medicare because of a disability. CSI answers that some individuals may qualify for coverage with a Medicare Advantage Plan, and that the companies offering Medicare Supplement policies to people over 65 also offer coverage to those under 65.1

Buying a Medigap policy before 65 does not use up the window at 65. Medicare's guide says that if you already have Medicare Part B, you'll still get a Medigap Open Enrollment Period when you turn 65.1

What If Your Medigap Company Leaves Montana or Goes Bankrupt?

CSI's Medicare FAQ gives Montana policyholders a specific right when their insurer exits. If your insurance company no longer operates in Montana, CSI says you have the right to buy another Medicare Supplement Plan A, B, C, D, F, G, K or L sold in Montana by another insurance company.1 CSI adds that you must apply for the new Medicare Supplement policy no later than 63 calendar days from the date your coverage ends.1

Two of the letters in CSI's list, Plans C and F, are closed to people new to Medicare on or after January 1, 2020, as the plans section below explains.1

Federal law adds a parallel right. Medicare's Choosing a Medigap Policy guide says you have a guaranteed issue right if your Medigap insurance company goes bankrupt and you lose your coverage, or your Medigap coverage ends through no fault of your own, and that you must apply no more than 63 days after your current Medigap policy ends.1 The same CMS guide notes that you may have additional rights under state law.1

Losing a Medigap insurer is only one of several federal guaranteed issue situations, and the plans available differ by situation. Brevy's national guide to Medigap guaranteed issue rights walks through the others.

Which Medicare Supplement Plans Can You Buy in Montana?

Medigap plans are identified by letter. Medicare's 2026 Choosing a Medigap Policy guide charts the Medigap plans as A, B, C, D, F, G, K, L, M and N, and states that all insurance companies that sell Medigap policies must offer at least Medigap Plan A.1

Plans C and F are closed to newer enrollees. Medicare's guide says Medigap plans sold to people new to Medicare on or after January 1, 2020 aren't allowed to cover the Part B deductible, so Plans C and F are no longer available to them; those buyers have the right to buy Plans D and G instead, which give the same benefits without covering the Part B deductible.1 Section 1882(z) of the Social Security Act is the statute behind the change: on or after January 1, 2020, a Medicare supplemental policy covering the Part B deductible may not be sold or issued to a newly eligible Medicare beneficiary.1

Medigap Plans E, H, I and J are no longer sold, but someone who already has one can generally keep it, according to Medicare's guide.1 Brevy's guides to how the lettered Medigap plans work and to Plan G versus Plan N compare the letters benefit by benefit.

Should You Pick Medigap or Medicare Advantage?

Medigap and Medicare Advantage don't combine. The CMS booklet Understanding Medicare Advantage Plans describes Medigap as extra insurance bought from a private company to help pay your share of costs in Original Medicare, and says you can't use a Medigap policy to pay Medicare Advantage Plan copayments, coinsurance, deductibles or premiums.3

The CMS booklet also sets two warnings for anyone moving between the two:

• If you're in a Medicare Advantage Plan, it's illegal for anyone to sell you a Medigap policy unless you're switching back to Original Medicare, and CMS says to report an attempted sale to your State Insurance Department, which in Montana is CSI.
• In most cases, if you drop a Medigap policy to join a Medicare Advantage Plan, you may not be able to get the same policy back.3,1

Federal law gives first-time Medicare Advantage members a way back. The CMS booklet says a person who joins a Medicare Advantage Plan for the first time and isn't happy with it has a "trial right" under federal law to buy a Medigap policy and a separate Medicare drug plan when returning to Original Medicare within 12 months of joining.3 CMS adds that some states provide additional special rights to buy a Medigap policy and tells readers to check with their State Insurance Department.3 Brevy's guide to switching between Medicare Advantage and Original Medicare covers the trial-right timing.

What Does Montana Law Protect After You Buy?

Montana statute adds two protections that apply once a Medicare Supplement policy is issued.

A 30-day free examination. MCA 33-22-908 requires every Medicare Supplement policy or certificate sold in Montana to carry a prominent notice that the applicant may return it within 30 days of delivery and have the premium refunded if, after examining it, the applicant is not satisfied for any reason.1 Federal law points the same way: Section 1882(c)(4) lets a Medicare supplemental policy be returned for a full refund of premiums during a period of at least 30 days after it is issued.4

Renewal while premiums are paid. Under MCA 33-22-924, if a person pays a Medicare Supplement renewal premium on the due date or within 31 days after it, the issuer may not refuse to renew the policy unless the issuer does both of these things:1

• refuses to renew all policies or certificates in Montana of the same form issued to persons of the same class; and
• offers a replacement policy or certificate at actuarially justified rates.1

Medicare's Choosing a Medigap Policy guide adds that any new Medigap policy issued since 1992 is guaranteed renewable even if you have health problems.1

Changing Medigap policies later is a different matter. Asked whether someone with Medicare Supplement insurance can change plans or companies, CSI answers that you can, but the new plan or company may not write a policy for you if you have any serious health conditions.1 Medicare.gov says that, under federal rights, you usually can't switch Medigap policies outside your six-month Medigap Open Enrollment Period except when you have a guaranteed issue right, and that switching outside the window may mean paying more and answering medical questions.4

Montana Medigap Rules at a Glance

The Montana Medigap table condenses the CSI Medicare FAQ, the CMS guide and Montana Code Annotated; the sections above carry the exact wording and limits.1,2

Who Can Help With Medigap Questions in Montana?

• CSI Consumer Services: The Montana Commissioner of Securities and Insurance takes Medicare Supplement questions at 800.332.6148 or 406.444.2040.1
• Montana SHIP: CSI says the State of Montana runs a free help program, the Montana State Health Insurance Assistance Program (SHIP), that offers trained, in-person help throughout Montana to Medicare beneficiaries and their families; call 1-800-551-3191.1
• 1-800-MEDICARE: For Original Medicare questions, 1-800-MEDICARE (1-800-633-4227) is the official line run by CMS, and TTY users call 1-877-486-2048; Medicare.gov says callers can reach a real person 24 hours a day, 7 days a week, except some federal holidays.5

Medicare's guide defines a SHIP as a state program funded by the federal government to give free local health insurance counseling to people with Medicare, and a State Insurance Department as the state agency that regulates insurance and can give information about Medigap policies.1 Brevy's Montana Medicare hub covers the rest of Medicare in the state, and the Montana Medicare Savings Programs guide covers help paying Medicare costs.

Learn More

Find personalized help timing your Montana Medicare Supplement window and checking your rights when an insurer leaves at brevy.com.

The information on Brevy.com is for educational purposes only and is not a substitute for professional legal, financial, or medical advice. Rules vary by state and program and change frequently. Always verify with the relevant agency or a qualified professional. Brevy is not a law firm, financial advisor, or healthcare provider.