Medicare Supplement

Medigap in Livermore: how the letter plans are standardized

For Livermore readers turning 65 — or helping a parent sort through Medicare mail — Medicare Supplement insurance (also called Medigap) is one of the most misunderstood pieces of the puzzle. It isn't Medicare Advantage. It isn't a drug plan. It's a private policy that pays some of the costs Original Medicare leaves behind, and it comes in standardized "letter" plans so you can compare apples to apples.

Here's a plain-English look at what Medigap does, what it doesn't, and how the letters work.

What Medigap actually does

Original Medicare pays a large share of your hospital and doctor bills, but not all of it. You're still responsible for deductibles, coinsurance, and copays — and unlike most job-based insurance, Original Medicare has no yearly cap on what you could owe out of pocket.

A Medigap policy is private insurance you buy to fill in those gaps. Depending on the letter plan you pick, it can cover things like the Part A hospital deductible, the 20% coinsurance under Part B, and extra hospital days after Medicare's coverage runs out. Some plans also help with skilled nursing coinsurance or limited foreign travel emergency care.

How the standardized letters work

In most states, including California, Medigap plans are sold using standardized letters set by federal rules. As of 2026, the plans available to new enrollees are A, B, D, G, K, L, M, and N. (Plans C and F are still held by people who were eligible for Medicare before January 1, 2020, but new enrollees generally can't buy them.)

Standardization matters because it makes shopping simpler. A Plan G sold by one insurer includes the same core benefits as a Plan G sold by another insurer. What can differ is the monthly premium, the company's customer service, and whether they offer any small extras.

For a side-by-side chart of what each letter covers, Medicare.gov's official comparison is the cleanest source.

What Medigap does not cover

This is where people get tripped up. Medigap generally does not cover:

• Prescription drugs — you'd need a separate Part D plan.
• Routine dental, vision, or hearing care.
• Long-term custodial care in a nursing home.
• Private-duty nursing or most cosmetic care.

Medigap also can't be used with a Medicare Advantage plan. You pick one lane: Original Medicare (often with Medigap and a Part D plan), or Medicare Advantage. If you're on Advantage and want to switch to Original Medicare with a Medigap, the timing rules matter — more on that below.

The Livermore angle

Livermore sits in Alameda County, where seniors have a wide field of Medicare options. Medicare Advantage plan availability is set at the county level, and Alameda County residents typically see dozens of Advantage and stand-alone Part D plans each year. Medigap works differently — it isn't tied to a county network — but California residents do have some of the strongest state-level Medigap protections in the country, including the "birthday rule," which gives current Medigap policyholders a yearly window to switch to an equal or lesser plan without medical underwriting.

For personalized help sorting through the choice, California's SHIP program is called HICAP (Health Insurance Counseling and Advocacy Program). Counselors are free and don't sell insurance.

Timing: when you can buy without health questions

The single most important date for Medigap is your 6-month Medigap Open Enrollment Period, which starts the first month you're 65 or older and enrolled in Part B. During that window, insurers must sell you any Medigap plan they offer at their standard price, regardless of your health history.

Miss that window, and outside of specific "guaranteed issue" situations or California's birthday rule, insurers can use medical underwriting — meaning they can charge you more or turn you down.

Note that Medigap's enrollment window is separate from Medicare's Annual Enrollment Period (October 15 – December 7) and the Medicare Advantage Open Enrollment Period (January 1 – March 31), which apply to Advantage and Part D plans.