How Excel handles percentages
Although formatting numbers as percentages is straightforward, the results you get after you apply the format may vary, depending on whether the numbers already exist in your workbook.

Formatting cells that already contain numbers If you apply the Percentage format to existing numbers in a workbook, Excel multiplies those numbers by 100 to convert them to percentages. For example, if a cell contains the number 10, Excel multiplies that number by 100, which means that you will see 1000.00% after you apply the Percentage format. This may not be what you expected. To accurately display percentages, before you format the numbers as a percentage, make sure that they have been calculated as percentages, and that they are displayed in decimal format. Percentages are calculated by using the equation amount / total = percentage. For example, if a cell contains the formula =10/100, the result of that calculation is 0.1. If you then format 0.1 as a percentage, the number will be correctly displayed as 10%. To learn more about calculating percentages, see Examples of calculating percentages.

Formatting empty cells If you apply the Percentage format to cells, and then type numbers into those cells, the behavior is different. Numbers equal to and larger than 1 are converted to percentages by default; and numbers smaller than 1 are multiplied by 100 to convert them to percentages. For example, typing 10 or 0.1 both result in 10.00%. (If you don’t want to display the two zeros after the decimal point, it’s easy to get rid of them, as explained in the following procedure.)
Display numbers as percentages
To quickly apply percentage formatting to selected cells, click Percent Style in the Number group on the Home tab, or press Ctrl+Shift+%. If you want more control over the format, or you want to change other aspects of formatting for your selection, you can follow these steps.

On the Home tab, in the Number group, click the icon next to Number to display the Format Cells dialog box.

In the Format Cells dialog box, in the Category list, click Percentage.

In the Decimal places box, enter the number of decimal places that you want to display. For example, if you want to see 10% instead of 10.00%, enter 0 in the Decimal places box.
Examples of calculating percentages
This section shows several simple techniques for calculating percentages.
Example 1: Increase or decrease a number by a percentage
Scenario If you spend an average of $25 on food each week, and you want to cut your weekly food expenditures by 25%, how much can you spend? Or, if you want to increase your weekly food allowance of $25 by 25%, what is your new weekly allowance?
If B2 is the amount that you spend on food, and C2 is the percentage you want to decrease that amount by, you can enter =B2*(1C2) in D2 to find the result:
In this formula, 1 is used to represent 100%. Similarly, if you wanted to increase the amount by a certain percentage, you would enter =B2*(1+C2) in D2:
Example 2: Calculate an amount based on a percentage
Scenario If you purchase a computer for $800 and there is an 8.9% sales tax, how much do you have to pay for the sales tax? In this example, you want to find 8.9% of 800.
If B2 is the price and C2 is the sales tax, you can type the formula =B2*C2 in D2, as shown here:
This formula multiplies 800 by 0.089 (the underlying percentage in decimal form) to find the sales tax to pay.
Example 3: Calculate the percentage based on two amounts
Scenario For example, if a student scored 42 points correctly out of 50 on a test, what is the percentage of correct answers?
In this scenario, if the number in B2 is points answered correctly and the number in C2 is the total points possible, you can type the formula =B2/C2 in D2 to find the grade.
This formula divides 42 by 50 to find the percentage of correct answers. (In the example shown here, the grade is formatted as a percentage without any decimal places showing.)
Example 4: Calculate an amount based another amount and a percentage
Scenario For example, the sale price of a shirt is $15, which is 25% off the original price. What is the original price? In this example, you want to find 75% of which number equals 15.
If B2 is the sale price, and C2 is 0.75, which is 100% minus the 25% discount (in decimal form), you can enter the formula =B2/C2 in D2 to find the original price:
This formula divides the sale price by the percentage paid to find the original price.
Example 5: Calculate the difference between two numbers and show it as a percentage
Scenario For example, the earnings for your department are $2,342 in November and $2,500 in December. What is the percentage change in earnings between these two months? To do this task, use the subtraction () and division (/) operators in a single formula.
If B2 represents November earnings, and C2 represents December earnings, you can use the formula =(C2B2)/ (B2) in D2 to find the difference:
This formula divides the difference between the second and first numbers by the value of the first number to obtain the percentage change. (In the example shown here, the difference is formatted as a percentage with two decimal places.)