A change from 45 to 90 represents a positive change (increase) of 100% Use the formula found below on this webpage to find the percent change by replacing the given values: Percent change = [(45 - 90) / 45] x 100 = 100 % (increase) Where: 45 is the old value and 90 is the new value. In this case we have a positive change (increase) of 100 percent because the new value is greater than the old value.