How To Compare Medicare Advantage Plans Against Original Medicare

Ignore the ancillary perks first and run a total-cost simulation using your actual doctors and prescriptions, then weigh the trade-off between Advantage’s capped out-of-pocket spending and Original Medicare’s unlimited provider access.

The fatal mistake when you compare medicare plans

The most common error is comparing average monthly payments or the ubiquitous star ratings as if they were equal measures of value. A plan with no monthly charge looks irresistible until you tally the $350-per-day copay for a five-day hospital stay. Original Medicare’s Part A deductible covers that same stay with no daily coinsurance. The Centers for Medicare & Medicaid Services sets that deductible each year. For the current figure, check Medicare.gov. Star ratings are equally misleading. A 4.5-star plan still uses prior authorization for every MRI. Those ratings measure member satisfaction with customer service, not the financial shock of a plan’s maximum out-of-pocket limit. The deeper confusion is mistaking that ceiling for your expected spending. The ceiling is a cap, not a budget. A plan with a high cap looks safer than it is if you rarely need much care. A plan with a low cap can still ruin a year if you need a single brand-name drug that falls in a high tier. The only way to know which number matters is to calculate what you will actually spend, not what the plan promises to cap.

Run the numbers on your actual usage

Building a side-by-side projection takes thirty minutes with your Part D drug plan’s formulary, your last year’s Explanation of Benefits, and a list of every specialist you saw. Write down each prescription exactly as taken. Then look up the tier and copay on the Advantage plan’s drug list versus the standalone Part D cost plus your Original Medicare coinsurance. Do the same for every visit. A rheumatologist visit under Original Medicare’s 20% coinsurance becomes a flat copay under Advantage. But a surgeon who does not accept the plan’s network becomes a 100% out-of-pocket cost that no projection can ignore. Then add the real risk of prior authorization. If you take a biologic that requires step therapy, count the cost of two failed cheaper drugs before your approved one. Add the week of delayed treatment. The generic plan summary will never show these line items, but your own records will. Finally, add the Part B cost to both sides, because you pay it regardless. The federal government sets the standard Part B rate each year. Confirm the current amount at Medicare.gov. Then add the Part D late enrollment penalty if you delay coverage. Only after this exercise can you see whether the Advantage plan’s lower monthly cost is real savings or a transfer of risk onto you.

When the network makes the decision for you

There is a non-financial failure case that no cost projection can fix. A narrow network can exclude your cancer center, your neurologist, or the only hospital within fifty miles that handles complex cardiac surgery. Even a plan with no monthly charge is a bad deal if it forces you to drive two hours for a thirty-minute follow-up. It is also a bad deal if the plan’s prior-authorization team denies a scan your doctor insists is urgent. During a serious illness, the time spent appealing denials is not a cost line item. It is a week of delayed treatment that can change your outcome. If you have a rare condition, are mid-treatment for a chronic disease, or simply value the freedom to see any doctor who accepts Medicare, the network alone decides the question. In that case, no amount of monthly savings justifies the risk. Original Medicare plus a Medigap supplement is the only rational choice, regardless of what the comparison spreadsheet says.

The Medigap enrollment trap

The comparison is not a one-year decision, and this is where most people get permanently stuck. When you first enroll in Medicare Part B, you have a guaranteed-issue right to buy a Medigap policy from any insurer. There are no medical questions asked. The price cannot be increased because of your health. That right expires after six months. If you choose an Advantage plan instead, you lose it. Switch back to Original Medicare years later, after a new diagnosis, and insurers can reject you. They can exclude the pre-existing condition or charge a rate based on your health history. The result: you are locked into Advantage forever, even if your doctors leave the network or your drug costs explode. The trade-off is stark. Advantage offers a capped out-of-pocket limit, but that cap is often high each year. Original Medicare has no cap at all unless you buy a Medigap policy. The Medigap price buys that cap, typically a monthly range set by private insurers, plus the freedom to see any provider. Insurers file their rates with each state’s insurance department. Get exact quotes from your state’s official insurance marketplace. When you run the numbers, include the cost of that future option. Losing it is a permanent loss of choice that no monthly savings in year one can justify.

Frequently asked questions

Can I switch from an Advantage plan back to Original Medicare after a year?

Yes, but only during the annual Open Enrollment Period from October 15 to December 7 or a special election period. You also need guaranteed-issue rights to a Medigap policy. Without those rights, you can return to Original Medicare, but you may be denied a Medigap policy or charged more for it.

What happens to my Part D drug coverage if I switch from Advantage to Original Medicare?

You will need to enroll in a standalone Part D plan within two months of leaving the Advantage plan to avoid a late enrollment penalty. The Part D plan is separate from Medigap, so you must manage two policies instead of one.

Are Medicare Advantage plans ever the better choice for a healthy person?

For a healthy person who uses few services, stays in-network, and values a low monthly cost, an Advantage plan can cost less in a typical year. The risk is the future. If you develop a chronic condition, the network and prior-authorization rules become far more consequential. Your ability to switch to Medigap later is not guaranteed.

Does the Part B cost change if I choose an Advantage plan?

No, you pay the same Part B amount regardless of whether you choose Original Medicare or an Advantage plan. The federal government sets this standard rate. Verify the current figure at Medicare.gov. Some Advantage plans reduce or cover part of that cost as a rebate, but the amount you pay to Medicare is fixed.

What is the single most important number to compare?

Your estimated total annual cost, not the monthly payment, not the out-of-pocket ceiling, and not the star rating. That number includes monthly costs, deductibles, copays, coinsurance, and out-of-network costs based on your actual prescriptions and doctors. If you cannot calculate that number, you are not ready to choose.

That single exercise cuts through every sales pitch, star rating, and glossy brochure, because it converts the two very different insurance models into one number: your worst-case and likely annual expense. If you skip this step, you are not comparing plans; you are comparing marketing departments, and for a deeper dive into the full landscape, see the broader topic of healthcare & medicare: what to know and how to handle it.