Herman Cain’s 9-9-9 Plan would hit the poor hardest, according to calculations by Boston University economist Laurence J. Kotlikoff, using financial-planning software he designed called ESPlanner. He compared four hypothetical 45-year-old couples with two young children living in Texas at different income levels, and calculated how much they could afford to spend annually (in 2011 dollars) under three tax plans, including Kotlikoff’s Purple Tax. The couples must make the money last until they die at age 100.