= 1 - (discount_price / original_price)
If you have a discounted price and an original price, and you want to know the discount as a percentage, you can calculate the percentage discount using a formula that divides the discounted price by the original price and then subtracts the result from one.
How the formula works
In the example, the active cell contains this formula:
In this case, Excel first divides the discounted price in D5 (70) by the original price in C5 (90) to get 0.78, which is then subtracted from 1:
Note that the result is a decimal version of the percent, and must be formatted using the Percentage number format in Excel to display as a percentage.