Here's a claim that America has a de facto flat tax. News to me, but perhaps Ben Bateman or others can comment.
In a study for the National Bureau of Economic Research, Boston University economists Laurence J. Kotlikoff and David Rapson have found that our all-in marginal tax rate is 40%, give or take a bit. Yes, you read that right: 40%.
Most workers will pay about that much on each dollar of income when all taxes -- federal and state income taxes, sales taxes, taxes for benefit programs, etc. -- are considered.
As a consequence, a 30-year-old couple earning only $20,000 a year has a marginal tax rate of 42.5%, while a 45-year-old couple earning $500,000 pays at 43.2%. There are some exceptions: A 30-year-old couple earning $50,000 a year, for instance, pays 24.4%, and a 60-year-old couple making $150,000 a year faces a tax rate of 47.7%.
The average marginal tax rate on incomes between $20,000 and $500,000 is 40.3%, the median tax rate is 41.8%, and the standard deviation of all of those rates is 5.3 percentage points. Basically, most of us pay about 40%, plus or minus 5.3 percentage points.
There's a table with a bit more data at the bottom of the article.