Medigap, also called Medicare Supplement Insurance, is a private policy that pairs with Original Medicare to help pay the deductibles, copays, and coinsurance that Medicare leaves behind. This guide explains what it covers, how the plans are organized, when it makes sense to enroll, and how it differs from Medicare Advantage, along with a few California-specific rules worth knowing.
What Medigap is and what it covers
Medigap is sold by private insurers, but it only works alongside Original Medicare (Parts A and B), not with Medicare Advantage. When Medicare pays its share of a medical bill, your Medigap policy then pays some or all of the remaining costs, depending on the plan you choose: deductibles, coinsurance, copays, and, on some plans, emergency care during travel outside the country.
Medigap does not include prescription drug coverage. If you need coverage for your medications, you generally need to add a stand-alone Part D plan separately.
Medigap plans are standardized by letter
In most states, including California, Medigap plans are identified by a letter — such as A, G, K, L, M, or N — and the core benefits of each letter are standardized by federal law. That means a Plan G from one insurer covers exactly the same as a Plan G from another insurer; what can change between companies is the monthly premium, not the benefits.
Plans F and C, which used to cover the Part B deductible, are no longer available to people who became eligible for Medicare on or after January 1, 2020. Those already eligible before that date can keep them or, in some cases, still purchase them. For most people turning 65 today, Plan G is often the most comprehensive option still being sold.
When to enroll: your Open Enrollment Period
Your Medigap Open Enrollment Period lasts six months and starts the month you turn 65 and are already enrolled in Part B. During this window, an insurer must sell you any Medigap policy it offers, at the same price it charges a healthy person, without being able to deny you based on your health or ask medical questions to decide whether to accept you.
Outside that window — or if you buy Medigap later in life without a guaranteed issue right — the insurer can generally ask medical questions, charge a higher premium, or deny coverage altogether. That is why, for most people, enrolling in Medigap during that initial six-month period is the lowest-risk time to do it.
California has an uncommon additional protection: the birthday rule. Each year, during the 30 days following your birthday, you can switch your Medigap policy to another with equal or lesser benefits, with any insurer, without being asked medical questions. It is an annual opportunity to shop for a lower premium without losing your coverage or risking a health-based denial.
Availability, cost, benefits, and eligibility vary by person, product, contract, and insurance company, as well as by your service area. Guarantees are subject to the claims-paying ability of the issuing insurance company. Karla Arámburo is not affiliated with or endorsed by Medicare or the federal government.
Medigap vs. Medicare Advantage
Medigap and Medicare Advantage solve the same problem — the costs Original Medicare does not cover — in very different ways. With Medigap, you generally pay a higher monthly premium in exchange for low, predictable out-of-pocket costs, and you can see any doctor nationwide who accepts Medicare, with no networks or referrals.
With Medicare Advantage, the monthly premium is usually lower — sometimes zero — and the plan may include drugs, dental, vision, or transportation benefits, but you typically must use a provider network and follow referral or prior authorization rules. For a fuller comparison between the two approaches, read our guide on Medicare Advantage vs. Original Medicare, and our guide to Medicare Part D if you need to add drug coverage alongside Medigap.
A bilingual, local resource in Southern California
Karla Arámburo is a bilingual, licensed insurance agent serving Southern California, and comparing your Medigap options with her costs nothing and comes with no pressure to enroll. You can call or text (619) 321-8733, explore our Medicare services or see how these rules apply if you live in San Diego. This page is general education, not individualized advice or an enrollment recommendation.
Frequently asked questions
Can I have Medigap and Medicare Advantage at the same time?
No. Medigap is designed to pair with Original Medicare, not with Medicare Advantage. If you have a Medicare Advantage plan, it is generally not legal or useful for someone to sell you a Medigap policy at the same time.
Does Medigap include prescription drug coverage?
No. Medigap policies sold today do not include prescription drug coverage. If you have Medigap, you generally need to add a stand-alone Part D plan separately.
What is California's birthday rule?
California law lets you switch your Medigap policy to another with equal or lesser benefits, without answering medical questions, during the 30 days following your birthday each year. This is a protection not every state offers.
Can an insurer deny me a Medigap policy because of my health?
Outside your Medigap Open Enrollment Period or a guaranteed issue right, an insurer can ask medical questions and, in most states, deny you the policy or charge you more based on your health history.
Are Medigap plans with the same letter identical between insurers?
The core benefits of each plan letter (for example, Plan G) are standardized by law and identical regardless of the insurer. What can vary is the monthly premium, so it is worth comparing prices between companies for the same plan.
Can I use any doctor with Medigap?
Yes. Because Medigap pairs with Original Medicare, you can generally see any doctor or hospital in the United States that accepts Medicare, with no referrals or networks required.
Can I still buy Plan F or Plan C?
Plans F and C are no longer available to people who became eligible for Medicare on or after January 1, 2020. If you were already eligible before that date, you may still be able to purchase them.