Percentages are a fraction of a number based on 100 as the denominator. People use percentages for many reasons such as trade discounts, sales discounts, sales tax and shipping. A common example of the use of percentages is on test grades where students get their per cent right based on the number of correct answers to the number of incorrect answers. The basic formula for a percentage is amount divided by total. Microsoft Excel allows for quick, error-free calculation of percentages.

Type the amount in a cell. For example, a student received a score of 48 out of 60 on a test and wants to find his percentage. The student would type 48 in cell A1.

Type the total in an adjacent cell. In the example, the student would type 60 in cell B1.

Type "=amount cell/total cell" in an adjacent cell to the total cell. Replace amount cell and total cell with the cell addresses of the amount and total. In our example, the student would type, "=A1/B1" in cell C1. The total will display 0.8 in cell C1.

Highlight the cell with the decimal, and click "%" button under the "Home" tab to convert the decimal to a percentage.