We are currently running negatives on tax income - benefit payments for Medicare. From there over the next ten years, things go to hell in a handbasket very quickly:
https://www.cms.gov/ReportsTrustFunds/downloads/tr2010.pdfTry page 19 and look at the graph. We would have to raise payroll taxes about double just to get to short-term funding levels. Cap is not an issue because there is no Medicare cap. A special "Medicare" tax was imposed for high-income persons (200K up) in the ACA on investment income of 3.8%. However it doesn't get credited to the trust fund.
Also the way this works, unlike Social Security, the general fund pays for portions of Medicare already. So general tax increases are needed.
The easiest way to look at the total picture is to look at percent of GDP. In the year 2000, we spent less than 2.5% of GDP on Medicare. In 2010, it increased over a percentage point to about 3.6%. By 2020 it is supposed to be about 4%. By 2030 spending is supposed to be about 5% (more than double).
What this means in taxes is pretty steep. For example, 2010 GDP nominal was 14.6 trillion. 3.5% of that (we are not paying for it, we are borrowing the money) is 511 billion. 5% is 730 billion. Compare that to 2000's approximately 365 billion. Another source of required tax increases is that many of the poorer elderly, or elderly in nursing homes, also receive Medicaid to cover either the Medicare 20% payments, premiums or the cost of longer-term nursing home care. Taxes need to be raised to pay for that spending.
This assumes, btw, that the scheduled drops in Medicare reimbursements go into effect, and absolutely no one believes they will. If they did, a lot of Medicare patients wouldn't get medical services which is just another form of the Ryan plan.
Another way to look at this is intuitively easier. You figure the Medicare HI cost per beneficiary and allocate by worker/beneficiary ratio.
So for example:
In 2010 about 47 million people were covered by Medicare part A. In 2000 39,257 people were. In 2020, the estimate is 63,000, and in 2030 the estimate is 80,000.
In 2000, there were 3.4 workers per retiree. In 2010, there were 3. By 2030, we expect that to go to no more than 2.3. The 2010 premium for medicare was $461 a month or $5,532 a year.
So, roughly:
2000 worker's annual share = $1,627 or $135 a month.
2010 worker's annual share = $1,844 or $153 a month.
2030 worker's annual share = $2,405 or $200 a month.
This presumes no real rise in medical costs. There are other per-beneficiary costs for SMI (parts B, C & D), but this shows how quickly it escalates.
Another way to look at it is that the average household will need to pay the Medicare premium for one retiree, as well as their own insurance premiums. Fortunately there is no wage cap and ACA also added a high-income extra Medicare tax of 0.9% which starts in 2013, so higher income households pick up a burden proportionate to their income.
FICA rates also need to go up. For a lot of lower income households, an increase of federal tax burden of 5% is going to be brutal.