Change: subtract old value from new value. Example: You had 5 books, but now have 7. The change is: 7-5 = 2. Percentage Change: show that as a percent of the old value ... so divide by the old value and make it a percentage: So the percentage change from 5 to 7 is: 2/5 = 0.4 = 40%. Percentage Change is all about comparing old to new values. See percentage change, difference and error for other options.