Medicare Supplement

Medigap in Ontario: the plan letters California still sells to new enrollees

If you live in Ontario and are pairing Original Medicare with a Medigap policy, the menu is set by federal law and shaped by California's own rules. The plan letters are standardized — a Plan G is a Plan G, no matter which insurer's name is on the envelope — but which letters you can buy today, and how you can switch later, depends on when you first became eligible for Medicare and on state protections that go beyond the federal floor.

Ontario is in San Bernardino County, and the Medigap policies sold here are the same standardized California plans sold across the state. Below is what those letters cover, how they work alongside a Part D drug plan, and where to get personalized help.

The plan letters you can buy in California today

Medigap policies are labeled by letter, and each letter has the same core benefits no matter which company sells it. In California, people who became eligible for Medicare on or after January 1, 2020 can buy Plans A, B, D, G, high-deductible G, K, L, M, and N. Plans C and F remain available only to people who were eligible before that date, because federal law closed those two letters to newly eligible enrollees.

Each letter fills a different mix of the gaps in Original Medicare — things like the Part A hospital deductible, coinsurance for hospital and skilled nursing stays, and the Part B coinsurance. Plans K and L pay a percentage of covered costs rather than the full amount and include an annual out-of-pocket limit. High-deductible G works like standard Plan G once you meet a yearly deductible set by Medicare.

The table below lists every insurer selling Medigap in California and the letters each one offers.

How Medigap fits with Original Medicare and Part D

A Medigap policy only works if you are enrolled in Original Medicare — Part A (hospital) and Part B (medical). Medicare pays its share first, and the Medigap plan pays some or all of what is left, depending on the letter.

Medigap does not cover prescription drugs. If you want drug coverage, you add a stand-alone Medicare Part D plan. For 2026, Part D has an annual out-of-pocket cap of $2,100 and a maximum deductible of $615. The old coverage gap ("donut hole") was eliminated in 2025, so Part D now has three phases instead of four. If your drug costs are uneven from month to month, the Medicare Prescription Payment Plan lets you spread them across the calendar year at no extra cost.

Medigap is different from Medicare Advantage. You cannot have both at the same time, and Medicare Advantage plans usually include drug coverage while Medigap policies do not.

Which insurers sell Medigap in Ontario

The insurers listed for California are the ones authorized to sell Medigap statewide, including in San Bernardino County. Because the letters are standardized, the coverage inside a Plan G from one company matches the coverage inside a Plan G from another. What can differ between companies is the price, customer service, and how they handle claims and rate changes over time — details you should confirm directly with each insurer before you enroll.

You can see the full list of California Medigap insurers, along with the letters each one offers, in the table on this page.

California rules that shape your choice

Federal law gives you a six-month Medigap Open Enrollment Period that starts the month you turn 65 and are enrolled in Part B. During that window, you can buy any Medigap plan sold in California without medical underwriting.

California also has a "birthday rule." Each year around your birthday, you get a set window to switch to another Medigap plan with equal or lesser benefits — with your current insurer or a different one — without answering health questions. The exact length of the window and how insurers must handle it are set by state law, so check with the California Department of Insurance or HICAP for the current details before you shop.

Outside of these protected windows, insurers in California can generally use medical underwriting when you apply, which means your health history can affect whether you are accepted or what you are charged.

When to enroll or make changes

Your first chance to buy Medigap is your six-month Medigap Open Enrollment Period at 65. After that, the birthday rule and certain guaranteed-issue rights (for example, if a plan you had is ending) may give you additional opportunities.

Part D and Medicare Advantage have their own calendars. The Annual Enrollment Period runs October 15 through December 7 each year, and the Medicare Advantage Open Enrollment Period runs January 1 through March 31. Those windows do not apply to Medigap itself, but they matter if you also carry a Part D drug plan.

Higher-income enrollees should be aware of IRMAA, the income-related surcharge that raises Part B and Part D premiums. In 2026, IRMAA begins above $109,000 in income for a single filer.