Percentage equals an amount divided by a total and shows a portion of the total based on a 100-scale. You can calculate the simple percentage of an amount from a total in Microsoft Excel using a special formula. Additionally you can calculate an amount (if you know the total and percentage), total (if you know the amount and percentage) or percent differences between two numbers by using formulas in Excel.

## Calculate Percentage

Calculating a percentage requires that you know the amount and total to calculate. For example, if you score 34 (amount) out of 40 (total) on a test, you can calculate the percentage score. To do this, enter 34 in cell A1 and 40 in cell B1. Type "=A1/B1" in cell C1 to calculate the simple percentage of the amount and total, ".85" or "85%."

## Calculate Amount

You can also calculate the number amount if you know the percentage and total. For example, if you know a friend scored 70 percent on a test and you know there were 40 questions on the test, you could calculate how many questions your friend got right, or the amount. Enter ".70" (70 percent) in cell A1 and 40 in cell B1. Type "=A1*B1" in cell C1 to calculate the amount that 70 percent of 40 is, "28."

## Calculate Total

If you know the amount and percentage but do not know the total, you can calculate it using Excel. For example, if you know the price of an item on sale was $20 and you know that item is discounted 50 percent, you can calculate the original total price of the item. Enter 20 in cell A1 and "=1-.5" (100 percent minus 50 percent) in cell B1. Type "=A1/B2" in cell C1 to gain the original total, "$40."

## Increase or Decrease by Percentage

With Excel formulas you can increase or decrease a number by a specific percentage. Assume you make $10 per hour and you want a 25 percent increase in your pay. Type "10" in cell A1 and ".25" (25 percent) in cell B1. Enter "=A1*(1+B1)" in cell C1 to calculate a 25 percent increase of 10, which is 12.50. If you wanted to calculate a 25 percent decrease, enter "=A1*(1-B1)" in cell C1.