Everybody says up, right? While I can’t predict the future, I thought it would be interesting to see what the historical tax rates were for different income groups. Here is some data taken from the Congressional Budget Office about historical federal tax rates as a percentage of “comprehensive household income”, defined as pretax cash income plus income from other sources like rental income and dividends. Note that this isn’t the same as your marginal income tax rate, which is the tax rate on your last dollar earned; This is a percentage of all your income.

As a reference, here are the quintiles for annual household income as defined by the US Census Bureau in 2005:

1st Quintile: $0 - $18,500
2nd Quintile: $18,500 - ...