When you first sign up for Medicare, you quickly learn that Original Medicare, Parts A and B alone, leaves significant gaps. Hospital stays, doctor visits, and outpatient procedures all come with deductibles, coinsurance, and copays that add up fast. Two main options exist to cover those gaps: a Medicare Supplement plan (also called Medigap) or a Medicare Advantage plan. They work in completely different ways, and the right choice depends on your health, your finances, and how you use the healthcare system.
This guide walks through both options clearly so you can make an informed decision before the Annual Enrollment Period opens in October.
What Is Medicare Supplement (Medigap)?
A Medicare Supplement plan sits on top of Original Medicare. You keep Parts A and B, and the Supplement plan picks up most or all of the costs that Medicare leaves behind, such as the Part A hospital deductible, the 20 percent coinsurance under Part B, and excess charges from doctors who do not accept Medicare assignment.
Supplement plans are standardized by the federal government. A Plan G from one insurer covers the same benefits as a Plan G from any other insurer. What varies between insurers is the monthly premium. This makes comparison shopping straightforward: find the Plan G with the lowest premium in your zip code, and you get identical coverage for less.
The most popular Supplement plan in California right now is Plan G, which covers nearly everything except the Part B deductible ($257 in 2026). Plan N is another common choice with lower premiums but small copays for office visits and emergency room visits.
Important: Medicare Supplement plans do not include prescription drug coverage. If you choose a Supplement, you must enroll separately in a Part D drug plan to get coverage for your medications. Budget for both premiums together when comparing total costs.
What Is Medicare Advantage?
Medicare Advantage (Part C) is a completely different structure. Instead of keeping Original Medicare and adding a Supplement, you replace Original Medicare with a private insurance plan approved by Medicare. The plan must cover everything Original Medicare covers, but it typically uses a network of doctors and hospitals, and you pay copays and coinsurance when you use care rather than a high fixed monthly premium.
The tradeoff is predictability versus flexibility. With a Medicare Advantage plan, your monthly premium may be zero or very low, but your costs when you are sick depend on what care you need. With a Supplement, your monthly premium is higher but your out-of-pocket costs when you use care are minimal.
Medicare Advantage plans often include extra benefits that Supplements do not, such as dental cleanings, vision exams, hearing aids, fitness memberships, and transportation to medical appointments. For many California seniors on fixed incomes, these extras represent real savings.
To see what Medicare Advantage plans are available in your county, visit our guide to Medicare Advantage in California.
Side-by-Side Comparison
| Feature | Medicare Supplement | Medicare Advantage |
|---|---|---|
| Works with | Original Medicare (Parts A + B) | Replaces Original Medicare |
| Monthly premium | Higher ($100 to $300+ per month) | Often $0 to $50 per month |
| Out-of-pocket when sick | Very low (plan covers most costs) | Copays and coinsurance apply |
| Doctor network | Any doctor who accepts Medicare | Restricted to plan network |
| Referrals needed | No | Often yes (HMO plans) |
| Drug coverage | Not included (need separate Part D) | Usually included |
| Dental / Vision / Hearing | Not included | Often included |
| Travel coverage | Some plans cover foreign travel emergencies | Limited to service area |
Who Is Medicare Supplement Best For?
Medicare Supplement tends to work best for people who:
- Have ongoing health conditions or see multiple specialists regularly
- Travel frequently within the United States and want freedom to see any Medicare doctor
- Value predictable costs and are willing to pay a higher monthly premium for that certainty
- Have doctors or hospitals they are not willing to leave
- Are in good enough health to qualify for underwriting (or are in a guaranteed-issue window)
In California, the birthday rule is an important protection for Supplement policyholders. Every year during a 60-day window starting on your birthday, you can switch to another Medigap plan with equal or lesser benefits from any insurer, without medical underwriting. This means you can shop for a lower premium every year without risking denial. Most other states do not offer this.
Who Is Medicare Advantage Best For?
Medicare Advantage tends to work well for people who:
- Are generally healthy and do not expect heavy use of medical services
- Want extra benefits like dental, vision, or hearing coverage
- Are comfortable with a primary care doctor who coordinates their care
- Live in an area with strong Advantage plan networks (most California counties qualify)
- Are on a fixed income and need to keep monthly premiums low
California has one of the most competitive Medicare Advantage markets in the country. Counties like Los Angeles, San Diego, Orange, and the Bay Area counties have multiple high-rated plans with $0 premiums and robust benefits. If you want Spanish-language plan guidance, our sister site Beneficios Medicare has resources in Spanish that walk through extra benefits in detail.
The Cost Question: Which Is Actually Cheaper?
There is no single answer. The comparison depends on how much healthcare you use.
Consider two California seniors, both 68 years old. Maria pays $185 per month for a Medigap Plan G plus $35 for a Part D drug plan, totaling $220 per month or $2,640 per year in premiums. She has a knee replacement in October. Her out-of-pocket cost is zero beyond the Part B deductible she already paid. Total annual cost: about $2,897.
Robert pays $0 per month for a Medicare Advantage HMO plus $35 for drug coverage built in. He is healthy and sees his doctor four times during the year, paying $20 per visit. Total annual cost: about $80 in copays.
The math flips when Robert has a major health event. A hospital stay under Medicare Advantage could cost him $350 per day for days one through five, plus additional coinsurance. The plan's annual maximum out-of-pocket in 2026 can be as high as $9,350 for in-network care. Maria's Supplement would have covered all of that.
The honest answer: if you stay healthy, Advantage may cost less. If you get sick, Supplement almost always costs less. What you cannot know in advance is which scenario will apply to you.
How to Decide Before AEP
Rather than guessing, look at your actual situation:
- How many times did you use healthcare last year, and what did you pay out of pocket?
- Do you have doctors you cannot change, or are you flexible?
- What is your monthly budget for premiums?
- How do you feel about managing copays versus a predictable fixed cost?
These questions rarely have obvious answers on paper. A licensed Medicare agent can run actual cost scenarios using your specific medications, doctors, and health history to give you a realistic comparison. This service is free: agents are paid by the insurance carriers, not by you.
Want a side-by-side comparison for your situation?
A licensed Medicare specialist can compare Supplement and Advantage options available in your California zip code, using your actual medications and doctors.
Get a Free ComparisonFrequently Asked Questions
What is the difference between Medicare Supplement and Medicare Advantage?
Medicare Supplement works alongside Original Medicare and pays the gaps Original Medicare leaves. Medicare Advantage replaces Original Medicare with a private plan that uses networks and copays. You cannot have both at the same time.
Which is cheaper in California, Supplement or Advantage?
Advantage plans typically have lower monthly premiums, but you pay more when you use care. Supplement plans charge more per month but leave little out of pocket when you need medical services. Which costs less overall depends on how much healthcare you use each year.
Can I switch from Medicare Advantage to Medicare Supplement later?
Yes, but outside of guaranteed-issue periods, insurers in most states can require medical underwriting. California's birthday rule helps current Supplement holders switch plans, but it does not help someone moving from Advantage to Supplement for the first time outside of a qualifying event. A licensed agent can explain your specific options.
Does Medicare Supplement cover prescriptions?
No. You need a separate Part D drug plan if you choose Medicare Supplement. Factor in both premiums when comparing total monthly costs.
What is California's birthday rule for Medigap?
California's birthday rule gives Medigap policyholders a 60-day window each year, starting on their birthday, to switch to another Medigap plan with equal or lesser benefits without medical underwriting. It lets you shop for lower premiums annually without risk of denial based on health status.
The Bottom Line
Neither Medicare Supplement nor Medicare Advantage is universally better. Supplement offers predictability, freedom to see any Medicare doctor, and strong protection against large medical bills. Advantage offers lower premiums, extra benefits, and competitive options in California's large urban counties. The right choice is the one that fits how you use healthcare and what you can sustain financially month to month.
Take time before October to think through your health patterns and get a real cost comparison. The Annual Enrollment Period is your chance to make a change, and it only lasts 54 days. Starting the conversation now means you will be ready.