How to Use a Calculator for Percentages

The percent button on calculators is an invaluable tool.
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Math is everywhere; people use it every day for ordinary things, from budgeting for household expenses or special events to figuring out taxes and tipping servers at a restaurant. For the latter two items in particular, as well as for many other transactions, you need to know how to calculate percentages. The easiest way to do it is to use a calculator.


What is a Percentage?

"Percentage" or "percent" actually comes from a phrase, per cent, which means "per 100" or "out of 100". Using that, 100 percent means the entirety or the whole; 1 percent is the same as one out of 100, or one part of the whole; 45 percent means 45 out of 100, or 45 parts of the whole.

You can think of it in terms of a cake. If the cake is whole and unsliced, the cake is in one part, and it is 100 percent. If you cut the cake into 100 pieces and take away 40 pieces, you have taken away 40 percent of the cake, or 40 parts of the whole.


Numerically, a percentage can be represented as a regular number by moving the decimal point two places. For example, 5 percent is equal to 0.05; 50 percent is equal to 0.5; and 100 percent is equal to 1.

The Percentage Formula

To obtain a certain percent of a number, the formula looks like this:

y/number = %/100


If you're trying to figure out 5 percent of 300, the formula is y/300 = 5/100. Manually, you'd have to cross-multiply and solve for the value of y, which in this case is 15: y x 100 = 300 x 5, or y x 100 = 1,500, so 1,500 / 100 = y, or 15.

Calculating a Percentage of a Number with a Calculator

To use a calculator to figure out a percentage of a number, simply take the percentage amount, move the decimal point two to the left and multiply the numbers.


If you want to figure out 5 percent of 300, start with the premise that 5 percent is equal to the number 0.05. Then multiply 0.05 by 300, and you'll get 15. That means 15 is 5 percent of 300.

You can also use the percentage key on your calculator. To get 5 percent, enter 300 x 5 and then instead of hitting the equal sign, hit the percent key and then hit the equal sign. You'll get 15.

Example: Figuring Out a Restaurant Tip

Calculating a tip for a server at a restaurant is a common everyday situation where you might have to calculate a percentage. If you want tip your server the standard 15 percent and your bill after tax is $45.94, how much should the tip be?


Using your calculator, multiply 0.15 (which is 15 percent in numerical form) by $45.94, which, rounded, equals $6.89. That amount is your tip, which you can add to the total for a total payment of $52.83 on your credit card.

Example: Figuring Out Sales Tax

All states in the U.S. charge sales tax for the purchase of a lot of different items. If you're buying a new pair of shoes for $150 in a state that charges sales tax on clothing and the tax is 6 percent, what will you end up paying for the shoes?


The first way is to convert 6 percent to 0.06 and multiply 0.06 by $150, which is $9. That's your sales tax; added to $150, you're paying $159 for the shoes.

Another way is to convert the percentage and then add a one: 1.06. Multiply 1.06 by $150, and you'll get $159, which is the total. Adding the "one" to the percentage figure tells the calculator that you want to know the whole plus 6 percent.

Using a Percentage Calculator Online

Percentage calculators are also available online for quick plug-in of numbers; you can also download apps on your phone that calculate tips and tax.