Medicare itself is government insurance, but you can use private insurance to cover what Medicare does not
Medicare is a federal program run by the Centers for Medicare & Medicaid Services (CMS). It is not private insurance. However, you can buy private insurance plans that work alongside Medicare or replace parts of it. These private plans are sold by insurance companies but are regulated by Medicare rules. The two main types are Medicare Advantage (which replaces Original Medicare) and Medigap (which supplements it). Understanding which one fits your situation depends on what gaps in coverage matter most to you and how much you want to pay.
Key Takeaways
- Medicare Advantage is a private insurance plan that replaces Original Medicare and usually costs less in monthly premiums, but limits which doctors you can see and requires referrals for specialists.
- Medigap is private insurance that pays the costs Medicare does not cover — copays, coinsurance, and deductibles — and works alongside Original Medicare, not instead of it.
- Medicare Advantage plans often include dental, vision, and hearing coverage that Original Medicare does not, but you pay more out of pocket when you use services.
- Medigap plans have higher monthly premiums but lower out-of-pocket costs when you need care, and you can see any doctor who accepts Medicare.
- You can switch between these options during the annual enrollment period (October 15 to December 7), but missing the window can lock you into your current plan for a year.
Medicare Advantage: Private insurance that replaces Original Medicare
Medicare Advantage is a private insurance plan sold by companies like UnitedHealthcare, Humana, Aetna, and Cigna. When you enroll in Medicare Advantage, you give up Original Medicare (Parts A and B) and use the private plan instead. The federal government pays the insurance company a fixed amount each month to cover your care. Because of this, Medicare Advantage plans often charge zero or low monthly premiums — sometimes $0 per month — and may include extras like dental, vision, or hearing coverage that Original Medicare does not offer.
The trade-off is that Medicare Advantage plans use networks. You must see doctors in the plan's network, and you usually need a referral from your primary care doctor to see a specialist. If you go out of network (except in emergencies), you pay the full cost. Out-of-pocket limits exist — in 2024, the maximum is $8,300 for in-network care — but you can reach that limit quickly if you need frequent care. These plans work well if you are healthy, do not travel much, and want lower monthly costs.
Medigap: Private insurance that fills the gaps in Original Medicare
Medigap (also called Supplemental Insurance) is private insurance that pays the costs Original Medicare leaves behind: copays, coinsurance, and deductibles. You keep Original Medicare (Parts A and B) and buy a Medigap policy on top of it. When you see a doctor, Medicare pays its share first, then Medigap pays its share, and you pay what is left. Medigap plans are standardized — a Plan G from one company covers the same things as a Plan G from another — so you can compare by price alone.
Medigap premiums are higher than Medicare Advantage premiums (often $100 to $300 per month depending on your age and location), but your out-of-pocket costs when you use care are much lower. You can see any doctor in the United States who accepts Medicare, no referrals needed. Medigap works well if you have chronic conditions, see specialists regularly, or want predictable costs and maximum flexibility.
How to compare Medicare Advantage and Medigap side by side
| Feature | Medicare Advantage | Medigap |
|---|---|---|
| Monthly premium | Often $0 to $50 | Usually $100 to $300+ |
| Out-of-pocket limit | Yes (around $8,300 in 2024) | No set limit, but lower per-visit costs |
| Doctor choice | Network only (except emergencies) | Any doctor who takes Medicare |
| Referrals required | Yes, for most specialists | No |
| Dental, vision, hearing | Often included | Not covered |
| Travel coverage | Limited outside network | Covered anywhere in the US |
When you can switch between Medicare Advantage and Medigap
You can change your coverage during the Annual Enrollment Period, which runs from October 15 to December 7 each year. Changes take effect January 1. If you miss this window, you are locked into your current plan until the next enrollment period — with rare exceptions. One exception is if you move out of your plan's service area; another is if you lose employer coverage. Some people also have a right to switch without penalty if they enroll in Medicare Advantage for the first time within 12 months of turning 65.
If you are currently on Original Medicare and want to switch to Medigap, you have a six-month window after you first enroll in Medicare Part B to buy a Medigap policy without being denied or charged more for pre-existing conditions. After that window closes, insurance companies can refuse to sell you a policy or charge you higher premiums based on your health history. This is called may provide issue rights, and it is one of the most important important date in Medicare.
What happens if you have other insurance alongside Medicare
If you have employer coverage through a current job or a spouse's job, you may not need Medigap or Medicare Advantage right away. Your employer plan is primary, and Medicare is secondary. When you retire or lose that coverage, you have 63 days to enroll in a Medigap or Medicare Advantage plan without penalty. Missing this window means you may pay higher premiums later.
If you have Medicaid (state health insurance for low-income people), you cannot buy Medigap. Instead, Medicaid covers some of the costs that Original Medicare does not. Some people may have access to for both Medicare and Medicaid — called "dual may be able to access" — and should talk to their state Medicaid office about how the two programs work together.
How to find and compare plans in your area
Medicare.gov has a plan comparison tool where you enter your zip code and see all Medicare Advantage and Medigap plans available to you, along with their premiums, networks, and coverage details. You can also call 1-800-MEDICARE to speak with a representative who can walk you through your options. Some states have Health Insurance Counseling and Advocacy Programs (HICAP) that offer free, unbiased help comparing plans — search "[your state] HICAP" to find yours.
When you compare, write down the doctors and hospitals you use most, then check whether they are in each plan's network. Look at the formulary (the list of prescription drugs covered) if you take medications. Compare the total cost you would pay in a typical year — premiums plus expected out-of-pocket costs — rather than premiums alone. A plan with a $0 premium but high copays may cost more overall than a plan with a higher premium but lower per-visit costs.
Frequently Asked Questions
Can I have both Medicare Advantage and Medigap at the same time?
No. You can have either Medicare Advantage or Original Medicare with Medigap, but not both. If you enroll in Medicare Advantage, you automatically lose your Medigap coverage. If you later switch back to Original Medicare, you can buy Medigap again, but you may not have may provide issue rights and could face higher premiums.
Do I need Part D prescription drug coverage if I have Medicare Advantage?
Most Medicare Advantage plans include prescription drug coverage (Part D), so you do not need a separate Part D plan. However, check your plan's formulary to make sure your medications are covered. If you have Original Medicare with Medigap, you must enroll in a separate Part D plan or pay a penalty later.
What if my Medicare Advantage plan drops out of my area?
If your plan is no longer offered in your zip code, you have a special enrollment period to switch to a different plan without waiting for the annual enrollment period. Medicare will notify you by mail. You typically have until the end of the month after you receive the notice to choose a new plan.
Are there income limits for Medicare Advantage or Medigap?
No. Both are open to anyone on Medicare regardless of income. However, if your income is low, you may be able to get help paying premiums and out-of-pocket costs through the Medicare Savings Program or Low-Income Subsidy program — ask your state Medicaid office or call 1-800-MEDICARE.
Can I switch from Medicare Advantage to Medigap anytime?
You can switch during the annual enrollment period (October 15 to December 7). If you switch outside that window, insurance companies can deny you or charge you more based on your health. The exception is if you are within 12 months of first enrolling in Medicare Part B, in which case you have may provide issue rights for Medigap.