The Connecticut income tax was, at first, a flat rate of 4.5 percent. But that promise was broken at least five times after 1991 as the number of tax brackets expanded to seven and the top rate jumped to 6.99 percent. Politicians love to divide voters into different groups (tax brackets) and mug them one at a time. Divide and conquer. Massachusetts has a constitutionally mandated flat tax. It is 5.1 percent. Pennsylvania's flat tax is 3.07 percent. Illinois' flat tax is 3.75 percent. A flat tax is hard to raise. A progressive or graduated income tax is easy to increase.