The Consumer Price Index is calculated through the equation, CPI = (current period price/base period price) x 100 The base period is 1983. Solving the CPIs for 2000 and 2005 (2000) CPI = ($28.94/$16.35) x 100 = 177 (2005) CPI = ($32.54/$16.35) x 100 = 199 The difference between the CPIs of 2005 and 2000 is 199 - 177 = 22.