The Core Difference: How Each Plan Works
Medicare Supplement (also called Medigap) and Medicare Advantage are two different ways to cover costs that Original Medicare does not pay. They work in opposite directions, and which one makes sense depends on how you use healthcare and what trade-offs you are willing to make.
Medicare Supplement plans work alongside Original Medicare. You keep your Medicare card, see any doctor or hospital that takes Medicare, and the supplement plan pays some or all of the costs Medicare leaves behind — copayments, coinsurance, and deductibles. You pay a monthly premium to the insurance company, and Medicare pays its share first.
Medicare Advantage plans replace Original Medicare entirely. You get a new insurance card from a private company (usually an HMO or PPO). That company is responsible for all your Medicare-covered care. In exchange, Advantage plans often charge lower or zero premiums, but they come with networks, prior authorization requirements, and yearly out-of-pocket limits that Original Medicare does not have.
Key Takeaways
- Medicare Supplement lets you see any Medicare-accepting doctor without networks or referrals, but premiums are higher and you pay more upfront before the plan kicks in.
- Medicare Advantage has lower or no premiums and includes prescription drug coverage, but restricts you to in-network providers and requires approval for many procedures.
- Supplement plans have no yearly spending cap, so catastrophic illness costs the same as routine care; Advantage plans cap your out-of-pocket costs but may deny or delay care.
- Switching between plan types is easiest during your Initial Enrollment Period or Annual Enrollment Period; switching mid-year is difficult and may require medical underwriting.
- Your choice depends on whether you value freedom to choose doctors (Supplement) or lower premiums and drug coverage (Advantage).
When Medicare Supplement Makes Sense
Choose a Supplement plan if you have established doctors and specialists you want to keep seeing, or if you travel frequently and need care outside your home state. Supplement plans have no network restrictions — any doctor or hospital in the United States that accepts Medicare accepts your Supplement plan. You do not need referrals, prior authorization, or approval to see a specialist.
Supplement plans also make sense if you have a chronic condition that requires frequent specialist visits or if you are concerned about the cost of a major illness. Because there is no yearly out-of-pocket limit, you know exactly what your costs will be: your monthly premium plus whatever Original Medicare's deductibles and copayments are. Once you meet those, many Supplement plans (called Plan G and Plan N) cover the rest.
The trade-off is cost. Supplement premiums range widely depending on your age, location, and which plan letter you choose (Plan A, B, D, G, K, L, M, or N are the standardized options). Plan G, the most comprehensive, typically costs $150 to $300 per month, though this varies significantly by state and insurance company. You also pay Original Medicare's Part B deductible ($240 in 2024, though this changes yearly) before your Supplement plan begins paying.
When Medicare Advantage Makes Sense
Choose Medicare Advantage if your priority is a low or zero monthly premium and you are willing to use doctors within the plan's network. Most Advantage plans charge $0 to $50 per month, and many include prescription drug coverage (Part D) at no extra cost. If you take multiple medications, this bundled coverage can save hundreds of dollars per year compared to buying a separate Part D plan.
Advantage plans also cap your yearly out-of-pocket costs — typically between $4,500 and $7,500 depending on the plan. Once you hit that limit, the plan pays 100 percent of covered services for the rest of the year. This protection matters if you have a serious illness or injury that requires expensive treatment.
The restrictions are real, though. Most Advantage plans are HMOs, which means you must use in-network doctors and hospitals, and you need a referral from your primary care doctor to see a specialist. Some procedures require prior authorization — the plan must approve them before you have them done. If you go out of network without authorization, you may owe the full cost. PPO-style Advantage plans offer more flexibility but charge higher premiums and copayments.
Comparing Costs: Premium, Deductible, and Worst-Case Spending
| Medicare Supplement (Plan G) | Medicare Advantage (typical HMO) | |
|---|---|---|
| Monthly premium | $150–$300 (varies by state) | $0–$50 |
| Part B deductible | You pay $240 (2024) | Plan pays after deductible |
| Doctor visit copay | $0 (after deductible) | $10–$50 per visit |
| Specialist copay | $0 (after deductible) | $25–$75 per visit |
| Yearly out-of-pocket cap | None | $4,500–$7,500 |
| Prescription drug coverage | Not included; buy Part D separately | Usually included |
| Network restrictions | None | Yes (HMO) or limited (PPO) |
The math depends on how much healthcare you use. If you see your doctor twice a year and take no medications, Advantage's low premium wins. If you see specialists monthly, take multiple drugs, and want to see doctors outside a network, Supplement's higher premium pays for itself quickly. If you face a $50,000 hospital stay, Advantage's out-of-pocket cap protects you; Supplement has no cap, but you know your costs in advance.
Switching Plans: When You Can and What It Costs
You can switch from Supplement to Advantage or vice versa during your Initial Enrollment Period (the seven months starting the month you turn 65 and enroll in Medicare Part B) without medical underwriting. After that window closes, switching becomes harder.
During Annual Enrollment Period (October 15 to December 7 each year), you can switch Advantage plans or switch from Advantage to Supplement without medical questions. However, if you switch from Supplement to Advantage after your Initial Enrollment Period, you may face a waiting period before coverage begins.
Switching from Advantage back to Supplement after your Initial Enrollment Period is the most restrictive. Some insurance companies will not sell you a Supplement plan, or will only sell you Plan A or Plan B (the most limited options). Others will sell you any plan but may charge more based on your health history. A few states have protections that require companies to sell you any Supplement plan, but not all do. Check your state's rules before you switch.
Network, Prior Authorization, and Access Issues
Advantage plans require you to navigate networks and approval processes that Supplement plans do not. If you see a doctor outside your plan's network without authorization, you typically pay the full bill yourself. Some Advantage plans allow out-of-network emergency care, but you must pay first and then fight for reimbursement.
Prior authorization means the plan must approve certain procedures, imaging, or specialist visits before you have them. This can delay care. If the plan denies authorization, you can appeal, but appeals take time and require documentation. Supplement plans have no authorization requirement — if Medicare covers it, your Supplement plan covers its share.
Advantage plans also change their networks and formularies (drug lists) every year. A doctor you see this year may not be in-network next year, or a medication you take may move to a higher cost tier. Supplement plans do not change coverage year to year — Plan G is Plan G whether you buy it in 2024 or 2026.
Prescription Drug Coverage: Part D vs. Advantage Bundling
If you choose a Supplement plan, you must also enroll in a separate Part D prescription drug plan. Part D plans vary widely in cost and which drugs they cover. You pay a monthly premium for Part D (typically $10 to $100 depending on the plan and your drugs) plus copayments when you fill prescriptions.
Most Medicare Advantage plans include Part D coverage bundled into one premium. This simplifies billing and often costs less if you take multiple medications. However, Advantage drug formularies can be restrictive — your medication may not be covered, or it may require prior authorization or a higher copayment than other plans offer.
If you take expensive specialty drugs or have complex medication needs, compare the actual cost of drugs under specific Advantage plans and Part D plans before you decide. The Medicare Plan Finder tool (at Medicare.gov) lets you enter your medications and see costs under different plans.
Frequently Asked Questions
Can I have both a Supplement and an Advantage plan at the same time?
No. You can have either Original Medicare with a Supplement plan, or an Advantage plan. You cannot hold both. If you enroll in Advantage, your Supplement coverage ends. If you later switch back to Original Medicare, you will need to enroll in a new Supplement plan.
What happens to my Supplement plan if I move to a different state?
Your Supplement plan may not be available in your new state, or the premium may change. Contact your insurance company before you move. If your plan is not available, you can switch to a different Supplement plan or to Advantage without medical underwriting if you move during Annual Enrollment Period. If you move outside the enrollment period, you may face restrictions.
Do I still get preventive care benefits with either plan?
Yes. Both Supplement and Advantage plans cover Medicare's preventive services — annual wellness visits, screenings, and vaccinations — at no cost. The difference is in how you access them and what happens if you need follow-up care.
What if my Advantage plan drops me or leaves my area?
If your Advantage plan is discontinued or no longer serves your zip code, you have a may provide right to switch to a Supplement plan without medical underwriting, even outside the normal enrollment period. This is called a Special Enrollment Period. Your insurance company must notify you at least 30 days before coverage ends.
Which plan is better for someone with multiple chronic conditions?
It depends on whether you want to see many specialists (Supplement is easier) or whether you want lower premiums and a spending cap (Advantage). Someone with diabetes, heart disease, and arthritis might prefer Supplement's freedom to see multiple specialists without referrals, but might prefer Advantage's lower premium and drug coverage if they are comfortable with one primary care doctor coordinating their care.