Suppose you have the discounted price and know the percentage discount, and you need to know the original price (price before discount). It's easy to calculate using a simple formula that divides the discounted price by the result of 1 minus the discount.
Excel / Spreadsheet Formula
=price/(1-discount)Where price is the actual price paid (AKA sale price, discounted price) and discount is the decimal value corresponding to the percentage discount (so .2 for a 20% discount, etc.).
Example
For example, maybe you purchased a used car for $800, and the sleazy used car salesman lured you in with the fact that the car was on sale with a discount of 60%. After getting home with the car, you are left wondering what the full cost of the car was before discount.
We'll translate the 60% discount to .6 for our discount variable in the formula:
=price/(1-discount)
=800/(1-0.6)
=800/0.4
=2000After calculating that the original full price of the $800 used car is actually $2000 dollars, you can now rest easy knowing that you got a great deal from the friendly used car salesman.