How to calculate percentages is easier than you think. Learning this can help you to easily calculate tips at restaurants and how to use percentages to easily calculate sales prices when shopping.
If you’re not sure how to perform any of those handy calculations, or if you’re just in need of a general percentage refresher, check out our guide on how to calculate percentages below.
To calculate a percentage, the whole amount must be known. This is in addition to the percentage or portion amount. You may be asked “what percentage of W is P,” where W is the whole amount and P is the portion amount. Or the question may be “how much is X percent of W,” where X represents a percentage figure.
A percentage is a way to express a number as a part of a whole. To calculate a percentage, we look at the whole as equal to 100%. For example, say you have 10 apples (=100%). If you eat 2 apples, then you have eaten 2/10 × 100% = 20% of your apples and you are left with 80% of your original apples.
The term “percent” in English comes from the Italian per cento or the French pour cent, which literally mean per hundred.
For instance, let’s say we have a jar containing 1199 red marbles and 485 blue marbles, making it 1684 marbles in total. In this case, 1684 makes up a whole jar of marbles and will be set equal to 100%.
Let’s say we want to find out the percentage of the jar that is taken up by the 485 blue marbles.
In our example, we need to find out what percent 485 (number of blue marbles) is of 1684 (total number of marbles). Therefore the fraction, in this case, is 485/1684.
To turn 485/1684 to a decimal, divide 485 by 1684. This comes to 0.288.
Formula: 485/1684 = 0.288
Multiply the result obtained in the step above by 100. For this example, 0.288 multiplied by 100 equals 28.8 or 28.8%.
Formula: 0.288 x 100 = 28.8 or 28.8%
A simple way to multiply a decimal by 100 is to move the decimal to the right two places.
You may come across a question that will ask you to work backward and find the original price of something after the price has increased. If you are given a quantity after a percentage increase or decrease, you may need to find the original amount.
Sometimes you’re given the percentage of an amount and need to know the numerical value of the percent. Examples include calculating taxes, tips, and loan interest.
Say you borrowed money from a friend who is going to charge you interest. The amount borrowed was initially $15 and the interest rate is 3% per day. These are the only two numbers you need for the calculation.
Multiply the percent by .01 or simply move the decimal to the left two places. This turns 3% into .03.
Formula: 3% x .01 = .03
In this case, multiply 15 by .03. This comes to 0.45. In this example, $0.45 is the amount of interest accrued each day that you do not pay your friend back.
Formula: 0.3 x 15 = .45 (amount of interest accrued)
Doing your shopping but want to save money by picking discounted items? Learning how to solve discount percentages will help you learn if you are actually saving money or wasting money.
This is a very simple way to calculate a discounted price, but you must begin with an accurate percent off. Double check what your item is on sale for.
The opposite of a percent is 100% minus the percent you are working with. If you want to buy a shirt that is 30% off, the opposite of this is 70%.
Formula: 100% – 30% (discount) = 70 %
To convert a percent to a decimal, multiply it by .01 or move the decimal two places to the left. In this example, 70% becomes .7.
Formula: 70% x .01 = .7
If the shirt you want is $20, multiply 20 by .7. This comes to 14. This means the shirt is on sale for $14.
Formula: $20 (item price) x .7 = 14 (discounted item price)
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