For Federal Income tax you can get the actual numbers from the IRS Tax stats webpage. There are a few complications to figuring this out including:
- The IRS numbers are broken down by Income into ranges, so getting exactly 20% is tricky.
- These numbers only include people who filed a tax return, people with no income are not included in these numbers, but I assume you meant to include them in your 20% number
- A lot of people file jointly, these numbers are based on the # of returns, not people.
What I was able to calculate in my trusty Excel spreadsheet that is close to an answer is this:
Top 16.7% by adjusted gross income ($100K+) pay 69% of the federal income taxes.
The top 27.7% by adjusted gross income ($75K+) pay 79.5% of federal income taxes.
So to get technical the claim that 20% pay 80% is false since the top 27% don't pay quite that much. That said, the numbers aren't so far off that the underlying point doesn't have merit.
The numbers get more lopsided if you look at the tippy top of income earners with the top 1% paying almost 27.6% of all federal income taxes.
Note: These are 2009 numbers. They, of course, vary by year.