How to Calculate a Percentage (Formulas and Examples)
4 min read
Percentages come up constantly - tips, discounts, test scores, interest, and price changes. Almost every real question is one of three types, and each has a simple formula.
Here is how to calculate a percentage by hand, with worked examples, plus a free calculator for when you just want the answer.
Step by step
- 1Percent of a number
To find X% of a number, multiply the number by X/100. Example: 20% of 80 = 80 x 0.20 = 16. Use this for tips and discounts.
- 2What percent one number is of another
Divide the part by the whole and multiply by 100. Example: 30 out of 120 = 30 / 120 x 100 = 25%. Use this for scores and shares.
- 3Percentage increase or decrease
Subtract the old value from the new, divide by the old value, and multiply by 100. Example: a price rising from 50 to 65 is (65 - 50) / 50 x 100 = 30% increase. A negative result is a decrease.
- 4Check it with the calculator
Plug your numbers into the Percentage Calculator to confirm the answer or skip the arithmetic entirely.
Tips
- To take a percentage off a price quickly: 25% off means you pay 75%, so multiply by 0.75.
- Percentage points are not the same as percent - going from 10% to 12% is 2 percentage points, but a 20% relative increase.
- To reverse a percentage (find the original before a markup), divide rather than multiply: an item that is 120 after a 20% increase was 120 / 1.20 = 100.
Frequently asked questions
How do I find what percent one number is of another?
Divide the part by the whole and multiply by 100. For example, 45 out of 90 is 45 / 90 x 100 = 50%.
How do I calculate a percentage increase?
Subtract the original from the new value, divide by the original, and multiply by 100. From 200 to 250 is (250 - 200) / 200 x 100 = 25%.
How do I take a percentage off a price?
Multiply the price by (100 minus the discount) / 100. A 30% discount on 60 is 60 x 0.70 = 42.