California Medicare quick facts (2026)

• Beneficiaries: Roughly 6.7 million Californians are enrolled in Medicare — the largest Medicare population of any state.
• Active Advantage carriers: Kaiser Permanente, UnitedHealthcare, Anthem Blue Cross, Blue Shield of California, Health Net, SCAN, Humana, Aetna, Alignment, Brand New Day, and others (presence varies sharply by county).
• State Medicaid program: Medi-Cal — relevant for dual-eligible (Medicare + Medi-Cal) coordination through D-SNPs.
• State quirk: California's Birthday Rule applies only to Medigap (Medicare Supplement) policies, not to Medicare Advantage.

Common California Medicare questions

Q: Can I switch Medigap plans in California without underwriting?
A: Yes — under California's Birthday Rule. For 30 days starting on your birthday each year, you can switch to a Medigap policy with equal or lesser benefits from any carrier without answering health questions. Confirm the exact window with the new carrier before you cancel anything.

Q: Does the California Birthday Rule apply to Medicare Advantage?
A: No. The Birthday Rule is a Medigap (Medicare Supplement) rule only. Medicare Advantage changes happen during the federal Annual Enrollment Period (Oct 15 – Dec 7) or the Medicare Advantage Open Enrollment Period (Jan 1 – Mar 31).

Q: How many Medicare Advantage plans are available in California?
A: It depends on your county and ZIP code. Large metro counties (Los Angeles, Orange, San Diego, Santa Clara) typically offer dozens of Advantage plans; rural counties may have far fewer.

Q: I have Medi-Cal and Medicare — what should I look at first?
A: Dual-Eligible Special Needs Plans (D-SNPs) coordinate Medicare and Medi-Cal benefits in one plan. Eligibility and plan availability vary by county.

Run the numbers for your situation: enrollment calculator · IRMAA calculator · Part D cost calculator.

Medicare basics in California

Medicare is a federal program, so the core rules are the same in California as everywhere else — but the specific plans available, premiums, and carrier networks vary by ZIP code and by county.

Most California residents become eligible for Medicare at 65 through Social Security. See our eligibility guide for the full rules including disability and ESRD.

For the 7-month enrollment window timeline, see Turning 65.

What California residents typically compare

• Medicare Advantage — Many California counties have 20-50+ Advantage plans to choose from. Plans, premiums, and extras vary by county.
• Medicare Supplement (Medigap) — Plans are standardized federally, but premium pricing and underwriting rules vary by state. California has its own Medigap pricing rules.
• Part D prescription drug plans — Available statewide, but formularies (covered drug lists) and preferred pharmacy networks differ by plan.

See Advantage vs. Supplement for the side-by-side framework.

California Medigap timing rules

The federal Medigap Open Enrollment window is the same everywhere — 6 months starting the month you turn 65 AND have Part B. During that window, no medical underwriting.

Outside that window, most states (including California unless otherwise noted) allow Medigap carriers to use medical underwriting — meaning they can deny you or charge more based on health. A few states have year-round guaranteed-issue rules. Check California's State Health Insurance Assistance Program (SHIP) for current rules.

See our switching from Advantage to Medigap guide for the timing trap.

How to compare plans in California

1. Confirm your ZIP code — plans differ within California by county
2. List your prescriptions and check each one on the plan's formulary
3. Confirm your doctors are in-network
4. Compare premium + deductible + maximum out-of-pocket
5. Check star ratings for plans you are weighing
6. Ask about prior authorization requirements (common on Advantage)

Use our comparison framework to keep it organized.