Thanks! As we live in the UK it didn't seem necessary to pay for a medicare B plan, but I sure do get the feeling it's worth paying for if you live in the US!
Medicare plan A is free to most people. Medicare plan "B" runs roughly $165 a month and covers doctors' services, most tests, etc. Or, rather, up to about 80% of those fees. And it doesn't cover all tests, although usually if the doctor recommends something it does cover. I have purchased a "Medi-Gap" plan that covers that 20%, at a cost of about another $185 a month.
You wouldn't think, from the sound of it, that 20% could be that much, but oh, dearie me, it certainly can be. One set of labs that I had a couple of years ago cost about $5,400. So, 20% of that, plus 20% of a CAT scan and MRI, plus a sonogram, plus the GP visits (plus co-pay of $20) made the Medigap a no-brainer. The full charges for my GP, had I been paying cash for my last 15 minute visit, would have been over $500. So between Part B (that has about a $225 per year deductible) and my Medigap plan, because I'd already paid the deductible for 2023, my visit cost a total of $20 and there were no charges for any of the labs or other tests that were done (courtesy of Part B). The big appeal of Part B plus a Medigap plan is that I can see any doctor in the country, as long as they accept Medicare and are willing to take me on a a patient. I also have to have a Plan D for pharmacy benefits. There are dozens of those as well, but I'm on a cheap plan at $10 a month with small co-pays for medication. Because I have no significant medication needs, that works. Otherwise I might need to change to a plan that covered specialized medicines with a higher premium cost.
A lot of people go with a Medicare Advantage plan, (Plan C, I think). It folds Plan A, Plan B, and usually Plan D into one program run by an entity other than the government, with the government's blessing. It's usually ~ much ~ cheaper, but is managed care. You have to see specific doctors, the plans each have specific things they'll pay or not pay, and there can be some sizable deductibles per year. Medication is folded into those plans as well, but there may be limits on which medications they'll pay for - even if a doctor orders one, they may not pay for it. And there can be "gotchas" involved. As in, it's possible that if you're in the hospital in the last week in December and have like a $4,500 out of pocket amount per year that you have to pay before the plan kicks in, when January rolls around you get to pay another $4,500 if you are still in the hospital, even for the same illness/reason. The devil is in the details of those plans. There are dozens of them and they're all different.
It sounds and it is complicated - you really have to do you homework, because you're pretty much locked in for a year with what you select.