Medigap, also called Medicare Supplement Insurance, helps pay certain costs left by Original Medicare. It is a separate policy with a separate premium. It is not a replacement for Part B, a drug plan or Medicare Advantage.
What you are comparing
Standardized Medigap plans are usually identified by letters. Within the same standardized letter, core benefits are the same even when different insurers sell the policy. Prices and insurer practices can differ. Massachusetts, Minnesota and Wisconsin standardize policies differently. New Medigap policies do not include prescription drug coverage, so plan for that separately.
A practical comparison sheet has columns for the plan letter, premium, covered cost sharing, any deductible, pricing method and available discounts. Do not compare a policy letter with an Advantage plan name as if they describe interchangeable benefits.
Your six-month federal window
The federal Medigap Open Enrollment Period begins in the first month you are at least 65 and enrolled in Part B. It lasts six months. During this window an insurer cannot use your health history to deny a policy it sells or charge more because of health conditions. Rules about a possible waiting period for pre-existing-condition coverage are separate.
This is not the October-to-December Medicare plan enrollment period. Starting Part B while still working can start the Medigap clock, even if you have not retired.
Outside that window
Medical underwriting may apply unless you have a guaranteed issue right or another state protection. Certain loss-of-coverage situations and trial rights may protect you, but the qualifying event, policy choices and application deadline matter. Preserve termination notices and prior coverage records. Do not assume every voluntary cancellation creates a protected right.
If you have Medicare before 65
Federal law generally does not require insurers to sell Medigap to people under 65. State rules may provide access. When you reach 65 with Part B, a new federal Medigap enrollment opportunity becomes important even if you have had Medicare for years.
Before changing a policy
- Identify the exact enrollment protection you are using.
- Ask whether underwriting or a waiting period applies.
- Get the new policy’s acceptance and effective date in writing.
- Coordinate drug coverage separately.
- Confirm cancellation and any trial or free-look requirements before ending the old arrangement.
Common question: Does a fall enrollment window guarantee Medigap acceptance? No. Check Medigap rights separately from the right to change a health or drug plan.
Understand underwriting before making a switch
Underwriting means an insurer evaluates health information under applicable rules when deciding whether to issue a policy or what it will charge. That is different from choosing a standardized benefit letter. A policy can have benefits you want while its acceptance requirements are an obstacle. Answer applications accurately and ask for clarification if a health-history question is unclear.
If you are leaving other coverage, gather the notice explaining why it ends. A plan leaving an area and your own decision to cancel are not interchangeable events. The available guaranteed issue policies and filing deadline depend on the specific protection. Ask for the applicable right to be identified before counting on it.
A working-past-65 example
Consider someone who keeps qualifying employer coverage and delays Part B until retirement at 67. Their Medigap timing may begin with the later Part B start. Compare that with a coworker who enrolled in Part B at 65 while keeping the employer plan. The coworker’s initial six-month federal Medigap window may already have passed. The same retirement date does not create the same Medigap situation.
Questions about the premium
- How is the policy priced, and how can its premium change?
- Is a quoted discount conditional on household enrollment or payment method?
- Does the quoted rate include all applicable fees or discounts?
- Does the policy have a high-deductible version, and is that what was quoted?
- Which benefits remain my responsibility under this lettered plan?
Does a Medigap policy cover services Medicare excludes? Do not assume it does. Its central role is paying specified Original Medicare cost sharing. Some policies have particular additional benefits, but a supplement is not a general promise to pay every rejected bill.
Sources and update notes
Published by My Coverage Relay. Updated September 24, 2026. This guide explains general rules; individual eligibility, plan terms and state protections require a specific review.