The percentage decrease formula calculates the size of a loss as a percentage of the original value. This makes it easier to compare losses of different sizes. For example, if a major metropolitan area has a population decrease of 5,000, the percentage decrease would be much smaller than if a small town had the same 5,000 decrease in population. Similarly, percentages are often used in investments to measure the performance of an investment account. To find the percent decrease, you need to know the starting and ending amounts.

Enter the starting value. For example, if you want to find the percent decrease of an investment portfolio and at the start the portfolio was worth $33,000, enter "33,000."

Push the subtraction sign.

Enter the ending value. In this example, if the value of the portfolio decreased to $31,000, enter "31,000."

Push the equals sign. The calculator will display the amount of the loss. In this case, the calculator will display "2,000."

Push the division key.

Enter the original value. In this example, enter "33,000."

Push the multiplication sign. The calculator will display the result of the loss divided by the original value. In this example, the calculator will display 0.0606060606.

Enter "100" and push the equals sign to have the calculator display the percentage decrease. In this example, the calculator will display "6.0606," meaning the portfolio decreases by just over 6 percent.