Medicare provides health insurance to over 70 million Americans. During Medicare open enrollment, which runs from Oct. 15 to Dec. 7 this year, people can enroll in the program or change plans.

You can also switch from original Medicare to a Medicare Advantage plan (or vice versa), and weigh your Part D prescription drug plan coverage against other options.

If you choose original Medicare (Part A and Part B), you can also buy a Medicare Supplement Insurance (Medigap) policy from a private insurance company to cover services and out-of-pocket costs not covered by original Medicare.

Note: You can only buy Medigap if you have original Medicare. That means you must sign up for Medicare Part A and Part B before you can buy a Medigap policy.

Medigap open enrollment

According to Medicare, the Medigap open enrollment period is a six-month window that starts on the first day of the first month you or you and your spouse are both age 65 or older and enrolled in Medicare Part B (medical insurance). During these six months, you can enroll in any Medigap policy an insurance company sells, and you can’t be denied coverage for any pre-existing health problems.

After the six months, that special protection ends. In most states, you can still apply later, but insurers can then use medical underwriting (they can deny you or charge higher premiums based on your health).

After six months, you might not be able to buy a Medigap policy, and if you can, it may cost more. The Medigap open enrollment period only happens once and doesn’t repeat yearly like Medicare open enrollment.

What is Medigap?

Most states offer 10 different Medigap plans sold by private insurance companies. They're named A-D, F, G, and K-N, and the price is the difference between the plans.

Medigap Plan G provides the most comprehensive coverage available to newly eligible beneficiaries and continues to be the most popular plan, accounting for 46% of all policyholders in 2025 (2026 data for the full year is not yet available), according to KFF. Plan F came in second, roughly 30–36%.

You might also be able to buy another type of Medigap policy called Medicare SELECT, which is only available in some states. If you choose a SELECT policy, you have the right to change your mind and switch to a standard Medigap policy within 12 months.

If you live in Massachusetts, Minnesota or Wisconsin, Medigap policies are standardized differently. Medigap must follow federal and state laws meant to protect you, but illegal practices by insurance companies can happen, so do your research when shopping for a Medigap policy.

What does Medigap cover?

Medigap policies help cover out-of-pocket costs, such as co-insurance, copayments and deductibles associated with original Medicare — nationwide. Some Medigap policies might also cover foreign travel emergency care, which gives you an extra layer of well-being when you travel outside the U.S.

Note: Although plans E, H, I and J are no longer sold, they still cover foreign travel emergency care if you're enrolled in one of these plans. If you want prescription drug coverage, you can enroll in a separate Medicare drug plan (Part D).

What does Medigap not cover?

Although Medigap plans cover all or part of original Medicare’s additional fees, they don't cover everything, such as long-term care, elective surgeries, hearing aids, eyeglasses, vision and dental care and private-duty nursing.

Besides that, not all plans cover Part B deductibles. Also, Medigap plans sold after 2005 don’t include prescription drug coverage.

Pros and cons of Medigap insurance

Medigap covers items and services not covered by original Medicare and significantly extends hospital, skilled nursing and travel coverage. But there are a few disadvantages worth looking at before you sign up.

Medigap and Medicare have different open enrollment windows and policies

The initial enrollment period for Medicare is a seven-month window that starts three months before your 65th birthday, includes the month you turn 65 and the three-month period after your birth month.

If you fail to enroll in original Medicare during the initial enrollment period, you’ll get another chance during Medicare open enrollment, which runs from Oct. 15 through Dec. 7, 2026.

You have a six-month Medigap open enrollment period, which starts the first month you have Medicare Part B (medical insurance) and you’re 65 or older. During these six months, you can enroll in any Medigap policy, but after the six months, you might not be able to buy a Medigap policy, or it might cost more if you do.

The Medigap open enrollment period only happens once and doesn’t repeat every year, unlike Medicare open enrollment, so time is of the essence.

Still working? You can sign up for Medicare even if you’re still on your employer’s health plan.

(Kathryn Pomroy is a contributing writer for Kiplinger.com.)

©2026 The Kiplinger Washington Editors, Inc. All rights reserved. Distributed by Tribune Content Agency, LLC.