Subtract the first number from the second number. For example, if you want to find the percentage difference between 40 and 36, subtract 40 from 36 to get -4.
Divide the result by the first number. In this example, divide -4 by 40 to get -0.1.
Multiply the result by 100 to convert to a percent change. Completing this example, multiply -0.1 by 100 to get -10 percent, or a 10 percent decrease.
Add the two numbers together and divide the result by 2 to calculate the average of the two numbers. For example, if your two numbers are 36 and 40, add 36 and 40 to get 76 and divide 76 by two to find the average equals 38.
Subtract the first number from the second number to find the difference between the two numbers. In this example, subtract 36 from 40 to get 4.
Divide the difference by the average and multiply the result by 100 to find the percentage difference. In this example, divide 4 by 38 and multiply the result by 100 to find the percentage difference equals 10.53 percent.