Multiply by 100 to get percent decrease. The formula for percentage decrease is given by. If the percentage is an increase then add it to 100 if it is a decrease then subtract it from 100.
First consider the unknown original amount as x.
For this reason you could use the following formula which is exactly the same. Then we solve the problem as follows. So you must provide an original quantity and a new quantity. Summary To calculate the original number based on current value and known percentage change you can use a simple formula that divides the current value by the percent plus 1.