Updated August 3, 2026. Quick answer: prior authorisation is the clearest practical difference between the two systems. Original Medicare mostly does not use it; Medicare Advantage does. The federal watchdog has examined how it is applied, and two of its findings are worth knowing before you choose.
The difference, from Medicare’s own handbook
Original Medicare: “In most cases, you don’t need approval (prior authorization) for Original Medicare to cover your services or supplies.”
Medicare Advantage: “You may need to get approval (prior authorization) from your plan before it covers certain services or supplies.”
Prior authorisation is not inherently improper — it is a normal utilisation tool, and plans use it partly to fund the extra benefits and lower premiums that make them attractive. The question is not whether it exists but how it lands when you need care.
What the Inspector General found
In its 27 April 2022 report, Some Medicare Advantage Organization Denials of Prior Authorization Requests Raise Concerns About Beneficiary Access to Medically Necessary Care (OEI-09-18-00260), the HHS Office of Inspector General found that 13 percent of prior authorization denials reviewed met Medicare coverage rules – meaning those services likely would have been approved under Original Medicare.
That is the finding that matters for the coverage choice: a service the federal programme would have covered was denied by a plan delivering that programme’s benefits.
The appeal numbers, and their limits
An earlier OIG report, Medicare Advantage Appeal Outcomes and Audit Findings Raise Concerns About Service and Payment Denials (OEI-09-16-00410) (25 September 2018), found two things that belong together:
- “MAOs overturned 75 percent of their own denials during 2014-16, overturning approximately 216,000 denials each year.”
- “During 2014-16, beneficiaries and providers appealed only 1 percent of denials to the first level of appeal.”
Read them side by side. Most appealed denials were overturned, and almost nobody appealed. The practical lesson is unusually actionable: if you are denied, appealing is not a long shot, and the low appeal rate suggests most people do not know that.
Honest limit: 2014-2016 figures from a 2018 report; no more recent OIG overturn/appeal statistics were located this session. Treat those percentages as evidence about how the appeals process behaved in that period, not as a current-year statistic.
What this means for the decision
It is not a reason to rule out Medicare Advantage. It is a reason to weigh two things honestly:
- How much care you expect to need. Prior authorisation is invisible when you are well and central when you are not.
- Whether you would appeal. The process works reasonably often for those who use it, and it requires someone with the energy to pursue it — which is worth thinking about honestly in the context of your own later years.
The full comparison, and the network question, which behaves the same way.
General information drawn from Medicare, CMS and state insurance-department publications, not insurance advice. Medicare rules, plan availability and dollar figures change every year, and state rules differ. Every figure here is year-labelled and every source is named so you can check it against your own situation. We do not sell insurance and receive nothing if you buy a plan.