The simplest method to calculate a percent change is to subtract the original number from the new number, and then divide that difference by the original number and multiply by 100 to get a percent. For example, a change from 5 to 6 has a difference of 1, divided by the original 5 is 0.2, which is a 20 percent change when multiplied by 100.
A second method is to divide the new number by the old number, multiply by 100, and then subtract 100. For the increase from 5 to 6, dividing 6 by 5 yields 1.2, which is 120 percent. Subtracting 100 yields the correct answer of a 20 percent increase.