... even though there's no advantage to having two insurance plans at the same time.
Not quite. Especially outside of the narrow window you describe.
Medicare Parts A and B both only pay 80% of what they cover; you need to pay the remaining 20%. That's popularly known as the "Medicare Gap". You end up needing to cover that gap
with a second medical insurance policy.
Medicare Part C deals with private insurance to cover that gap along with some things that Medicare doesn't cover. Many, if not most, Part C plans include Part D (Prescription) coverage. Part C plans fall into one of two tracks:
- "Medi-Gap" insurance (AKA "regular Medicare" or "original Medicare") which just acts as secondary insurance such that Medicare pays first and then Medi-Gap gets billed for the remainder.
- Medicare Advantage was created in 1997. These plans take over and manage all your Medicare plans and billing.
Please note that Part C, just like Part D, only sets the standards and requirements for the
private policies sold by
private insurance companies as Medicare Part C coverage.
You pay your monthly Medicare Part B premium through a deduction from your monthly Social Security check (Part A was paid through years of payroll taxes) -- if you're not receiving Social Security, then Medicare bills you quarterly. Medi-Gap and Advantage plans would bill you directly, though some Advantage plans are structured to be "free" (and some will even refund you that Part B premium). As I said, you just hand the keys to your Medicare over to the Advantage plan and it does all the rest.
When you sign up for Part C coverage, you need to choose which track to travel. It is very difficult to switch tracks later and I think you are allowed to switch only once in your lifetime.
Please note that the TV ads flooding the airwaves and cable bandwidth misrepresent Medicare Part C as
only consisting of Medicare Advantage; not even a single mention of Medi-Gap plans even existing. That's a huge investment in advertising, especially considering how some are just giving these
private insurance plans away for free. How are they making any money off this? Well, they bill the government for your claims.
On YouTube, you can find many critics of Medicare Advantage, including talk show radio host
Thom Hartmann who has done extensive research on the American healthcare system and from whom I have heard criticisms of fraudulent billings and subjecting clients to the standard private insurance problems like needing to have treatment approved (and potentially denied) and being restricted to in-network providers.
Here is one video by Thom Hartmann on the subject:
https://www.youtube.com/watch?v=rqhBhbrXvwA&t=12s (would not embed)
Each state provides a Medicare counseling service called
SHIP (State Health Insurance Program), called
HICAP (Health Insurance Counseling and Advocacy Program) in California (and could go by yet other names in some other states). As described in our Medicare presentation at
OLLI, they will counsel you about your options, etc,
but they will not try to sell you on any given plan. They will provide you with the information you will need to make your own decision.
As for my own experience, I retired from the reserves 11 years ago when I turned 60, at which point my retirement benefits included Tricare health insurance. I also had group coverage from my civilian job, so I used the group coverage as the primary and Tricare as secondary. Immediate effect was that all medical expenses, including co-pays, were paid for and I had no out-of-pocket (I forget whether that also applied to prescription co-pays). When I turned 65, my Tricare coverage was converted to Tricare-for-Life which combined Medicare with Tricare acting as my Medi-Gap coverage (plus Part D). At that point, I opted out of my civilian job's group coverage, but kept the dental plan. After retiring from my civilian job, I'm on Tricare-for-Life supplemented by a federal employees' dental and vision plan.