Original Medicare and Medicare Advantage are two distinctly different ways to cover your healthcare expenses once you reach age 65. The decision is an important one. If you start out with Original Medicare and change your mind later, you can always switch from Original Medicare to an Advantage Plan during the Annual Open Enrollment period (Oct. 15 to Dec. 7). But switching from Advantage back to Original Medicare isn’t as simple.

If you drop your Advantage plan, you can go back to Original Medicare Parts A and B. And you’ll be able to sign up for any Medicare Part D – Prescription Coverage you choose, with no late enrollment penalty. Getting approved for a Medigap policy is where you may encounter problems. You only have guaranteed issue rights during your Medigap Open Enrollment Period – the 6-month period beginning with the first month you have Medicare Part B and you’re 65 or older. A guaranteed-issue period is when you can purchase whatever Medigap policy you choose, from any insurance company, with no medical underwriting.

There are a few limited situations other than your Medigap Open Enrollment Period where you would have guaranteed issue rights. (See the list of situations in Choosing A Medigap Policy, p. 22-23 and/or use Medigap decision tool on Medicare.gov.) But you can’t necessarily count on having a qualifying situation if or when you want to switch. In most states, the insurance companies can refuse to offer you any policy, only offer you certain policies, and/or charge you more because of your medical history. In some cases, they can also impose a 6-month waiting period before pre-existing conditions are covered.

Doing a thorough comparison of Original Medicare and Medicare Advantage plans can help you decide which path is the better one for you. This post will point out where they differ as to where you receive your medical care, whether there are hoops to go through to get that care, and the costs. As you read through this, you might make note of the points that seemed most relevant to you, to help you in your decision.

This post is part of a series about Medicare. Reading these two previous posts may help you better understand references to enrollment periods and the parts of Medicare:

• The Parts that Make up Medicare
• Medicare Enrollment Periods

Access to Doctors and Hospitals

Do you already have a primary physician, or a specialist, that you want to be sure you can continue to see? Do you frequently travel in other parts of the US or move to a warmer part of the country during winter? Do you have a complex health issue that requires care from a team of specialists? Your answers could affect whether Original Medicare or Medicare Advantage will fit you best. 

Original Medicare: You can see any doctor or use any hospital in the US that takes Medicare. 98% of doctors participate in Medicare and hospital participation is practically universal. “Participating” means that they will bill Medicare and accept the Medicare-allowed amount as payment in full. If you have Medigap insurance, Medicare will forward your claims to your Medigap plan without any action on your part.

Advantage Plans: The vast majority of Advantage plans are HMOs. For your care to be covered by an HMO, you must use an in-network provider except in emergencies. Networks are typically in a limited geographic area. Networks change; a doctor or hospital that is in your network this year might be out-of-network next year. This is one of the reasons you should compare plans every year if you have an Advantage plan.

Some Medicare Advantage plans are PPOs, which cover both in-network and out-of-network care. Your share of the cost is usually more for out-of-network care, and there is usually a significantly higher limit for out-of-pocket expenses than for in-network care.

Note: The Annual Enrollment Period for 2027 is the first time that you can check whether your doctor is in-network for any particular Medicare Advantage plan on Medicare’s Plan-Compare tool. But the results are accompanied by a warning: “Before you join a plan, check with your provider to make sure they’re in the plan’s network. Plan networks can change at any time. Providers with multiple office locations may be in network at one location and out of network at another.”.

Requirements Before You Receive Care

Original Medicare: With Original Medicare, you do not need a referral from your primary physician before you see a specialist. Original Medicare seldom requires pre-authorization. When it does, it is only for certain specific types of hospital outpatient procedures and durable medical equipment.

Medicare Advantage: Referrals and pre-authorizations are frequently required in Medicare Advantage HMO plans, although there is significant variation from plan to plan. Advantage PPOs typically do not require referrals and less frequently require prior authorization for services compared to Advantage HMOs.

For the past several years, the annual number of pre-authorizations has averaged a little less than two per Advantage plan enrollee (KFF). More than 90% of those are approved but the process can still affect patients’ care; an American Medical Association annual survey of primary physicians and specialists from 2025 reports negative impacts on patients including delayed care, patients abandoning the recommended treatment altogether, adverse health events, and higher overall utilization of health care resources.

How much will it cost?

Whichever path you choose, you will have several different types of expenses:

• Fixed costs
• Premiums for Medicare Part B
• Plus the premiums for additional policies you purchase: Part D and Medigap for those on Original Medicare, and the Advantage plan premium (if any) for those going the Advantage route.   
• Care-related expenses
• Deductibles are the amount you pay out-of-pocket before the insurance begins to pay for covered expenses
• Copays and co-insurance are your share of the cost of covered care. Copays are a set amount, such as $25 for a doctor’s visit or $5 for a generic prescription. Co-insurance is a percent, for example, 20% of the actual cost of the doctor visit or the prescription.
• Other expenses you may have are
  • Advantage HMO plans: Full cost for care out received out of network
  • Original Medicare:
    • Balance billing (excess charges) of up to 15% of the Medicare-approved amount by doctors who accept Medicare patients but do not accept assignment (Medicare’s approved cost)  (uncommon).
    • Full cost of care provided by healthcare providers who have fully opted out of Medicare (rare)

To compare the costs of Original Medicare to the costs of an Advantage plan, let’s look at fixed costs first, and then the care-related costs.

Explanation about the dollar amounts used in this table:

• The majority of people who choose Original Medicare also purchase a Medigap policy; the most frequently purchased plan is Plan G, so I will use premiums for Medigap Plan G in the fixed costs for Original Medicare.
• The plans available and the premiums vary between geographic locations. Medigap premiums can also vary by age, gender, and smoking status, depending on your state’s regulations. The Medigap rates used here are for a 65-year old female non-smoker.
• The costs used in the table below are an example, based on plans available in the Chicago suburbs of Illinois, and may not be representative of the prices in your area. If you received a printed copy of Medicare & You, Part D and Advantage plan details for your state are printed in the appendix. Or use Medicare’s Compare-Plan tool.
• Dollar amounts in red are for 2027. Amounts in black are for 2026, as not all 2027 numbers were available when this post was published.
• Costs not included in this example:
  • Prescription drug out-of-pocket costs, since the deductibles and out-of-pocket limits for Part D plans and Medicare Advantage drug coverage are very similar.
  • Higher premiums paid by higher-income recipients, called IRMAA (Income Related Month Adjustment Amounts). Like the base Medicare Part B premium, these are the same for both Original Medicare and Advantage enrollees.

Which path is right for you?

The 65+ population is clearly divided on which Medicare path is the best choice for them. As of 2026, 55% now have Advantage plans, meaning that around 45% choose Original Medicare.

Here are some points to consider

Original Medicare with Medigap Plan G gives you very predictable costs that are easy to budget for. The only out-of-pocket expense that will change from one year to the next will be the Medicare Part B deductible. Your costs on an Advantage Plan, on the other hand, can vary widely from one year to another based on how much care you need and where you receive it. An Advantage Plan could save you money in years when your health is good.

Perhaps the assurance that you can get care anywhere in the US, or from almost any provider in your area, is important to you. Then having Original Medicare would be more reassuring. Maybe you’ve had a bad experience with pre-authorization requirements and want to avoid them at all costs.

Maybe the “extras” such as some coverage for eyeglasses dental care are very appealing to you.

One thing to remember is, if you start on the Advantage Path and later want to go back to Original Medicare, your health status at that point could make it more expensive, more difficult, or even impossible to get a Medigap policy. KFF (a health policy group) estimated that 75% of the people on Medicare Advantage plans could be denied a Medigap policy based on pre-existing health conditions. There are certain situations where you might have a guaranteed right to purchase certain Medigap plans – for example, if your Advantage plan ends or is no longer avail able in your geographic area – but you can’t necessarily plan on that happening, or happening at the time you might need to switch.

Once you’ve chosen your path, you still have decisions to make. If you choose Original Medicare, you’ll also need to choose a Medigap policy and a Prescription Plan D policy. If you choose Advantage, you’ll probably have several companies and plans to select from there. The next post will show you how to use the Medicare Plan-Compare tool to help with that decision.