Medicare supplement insurance, commonly called Medigap, helps pay some of the out-of-pocket costs left by Original Medicare. It is sold by private insurance companies, but the benefits for each standardized plan letter are set by federal rules. This guide explains the basics without assuming that one type of coverage is right for everyone.

Educational note: This article is general information, not personalized insurance advice. Plan availability, premiums, underwriting, and enrollment rights can depend on your age, health, coverage history, county, and the rules in effect when you apply. No 2027 premiums or plan changes are assumed here.

How Medigap fits with Medicare

Original Medicare includes Part A hospital insurance and Part B medical insurance. You can generally see any doctor or other provider who accepts Medicare, anywhere in the United States. You must usually pay Part B premiums, deductibles, and coinsurance, as well as the full cost of services Medicare does not cover.

A Medigap policy works with Original Medicare. Medicare pays its share of an approved, covered service first, and the Medigap policy may then pay some of the remaining amount, depending on the plan. You must have Medicare Parts A and B to buy a Medigap policy, and you cannot use Medigap to pay costs for a Medicare Advantage plan. Medicare explains how Medigap works.

Medigap generally does not cover prescription drugs. If you want prescription coverage while keeping Original Medicare and Medigap, you usually consider a separate Medicare Part D plan. Before enrolling, check how drug coverage could affect your current coverage and whether you have creditable coverage through an employer or another source.

What Medigap may help pay

Depending on the plan letter, Medigap can help with costs such as:

Part A hospital coinsurance and additional hospital days after Original Medicare benefits are used
Part B coinsurance or copayments for Medicare-covered services
The first three pints of blood used for a covered procedure per benefit period
Skilled nursing facility coinsurance
Hospice care coinsurance or copayments
The Part A deductible, for plans that include that benefit
Emergency care during limited foreign travel, for plans that include that benefit and subject to plan limits

Medigap does not cover everything. It generally does not cover routine dental, vision, or hearing services, long-term custodial care, private-duty nursing, or prescription drugs. It also does not cover services that Medicare does not consider medically necessary. Review the policy and the official Medigap plan comparison before applying.

Standardized plan letters

In Texas and most states, standardized Medigap policies are identified by letters such as A, B, D, G, K, L, M, and N. A plan letter represents a package of benefits. The same letter generally provides the same standardized benefits regardless of the insurer, although premiums, discounts, customer service, and underwriting practices can differ.

Massachusetts, Minnesota, and Wisconsin use different standardization systems. If you move to or from one of those states, compare the state-specific rules instead of relying only on a plan letter.

Plan availability depends on what insurers offer in your area. Plans C and F generally are not available to people who became eligible for Medicare on or after January 1, 2020, because those plans cover the Part B deductible. People who were eligible for Medicare before that date may have different purchase rights. See Medicare’s plan guidance.

Your Medigap Open Enrollment Period

For most people, the one-time Medigap Open Enrollment Period lasts six months. It starts on the first day of the month in which you are both age 65 or older and enrolled in Part B. During this period, insurers generally cannot use your health history to deny you a policy or charge more because of a pre-existing condition. You can buy any Medigap policy sold in your state during this window.

This period is not the same as Medicare’s October 15 through December 7 Annual Election Period for Medicare Advantage and Part D. Medigap does not have an annual open enrollment period that repeats every year.

If you apply after your Medigap Open Enrollment Period, you may face medical underwriting, a higher premium, or a denial unless you have a guaranteed issue right or another protection under federal or Texas law. Medicare’s enrollment overview and the Texas Department of Insurance consumer resources explain these rules.

Guaranteed issue rights and switching coverage

Certain events can create a guaranteed issue right. Examples can include losing eligible employer or union coverage, leaving a Medicare Advantage plan because it left the service area, or using a trial right in a qualifying situation. The exact plans, deadlines, and proof requirements vary. Do not cancel existing coverage until the new coverage is approved and you understand when it begins.

Switching from Medicare Advantage to Original Medicare does not automatically guarantee the right to buy any Medigap plan at any time. Ask Medicare, your plan, or a licensed professional to confirm your specific right and deadline. Medicare lists situations that may provide Medigap protections.

Premiums and policy renewal

You pay a Medigap premium to the private insurer in addition to your Medicare Part B premium. Premiums can differ substantially for the same standardized plan. Insurers may price policies using methods such as attained age, issue age, or community rating, subject to applicable law. Premiums may also change over time.

Medigap policies are generally guaranteed renewable. An insurer cannot normally cancel your policy because your health changes, but coverage can end for reasons such as nonpayment of premiums, intentional material misrepresentation, or the insurer leaving the Medigap market under applicable rules.

A practical shopping checklist

Confirm that you have, or will have, Medicare Parts A and B.
List your doctors, hospitals, travel patterns, prescriptions, and expected care needs.
Compare standardized benefits, premiums, rate history questions, and household discounts where available.
Check whether you need a separate Part D plan.
Ask about medical underwriting and any guaranteed issue or trial right before switching.
Verify the company and agent through the Texas Department of Insurance consumer resources.
Read the policy when it arrives. If you are replacing coverage, avoid a gap and keep documentation of every application and effective date.

Before you act

Compare official plan benefits and premiums, then confirm Texas-specific rights with Medicare, the Texas Department of Insurance, SHIP, or a licensed professional. This guide is educational and is not a recommendation to buy a particular policy.

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