This calculator has three tabs. Each one solves a different type of percentage problem. Pick the tab that matches your question, fill in the numbers, and press Calculate.
Find Percentage: Enter a percentage and a number to find what that percentage of the number is. Example: 20% of 85.
What Percent: Enter a part and a whole to find what percent the part is of the whole. Example: 30 is what percent of 120?
Percentage Change: Enter an original value and a new value to find how much it changed as a percentage. Example: change from 50 to 65.
What Percentages Really Are
The word "percent" comes from the Latin phrase "per centum," which means per hundred. So when you say 45%, you are really saying 45 out of every 100. That is all it is.
Percentages connect directly to fractions and decimals. 45% equals 45/100, which equals 0.45. These three forms all say the same thing. Knowing that helps you switch between them easily. 50% is the same as one half. 25% is the same as one quarter. 10% is just divide by 10.
Common Percentage Formulas
What You Want to Find
Formula
Example
Percentage of a number
(P / 100) x N
20% of 85 = 0.20 x 85 = 17
What percent is X of Y
(Part / Whole) x 100
30 / 120 x 100 = 25%
Percentage change
(New - Old) / Old x 100
(65 - 50) / 50 x 100 = 30%
Percentage increase
Old x (1 + P/100)
50 x 1.30 = 65
Percentage decrease
Old x (1 - P/100)
80 x 0.75 = 60
Worked Examples
Example 1: 20% of 85
Use formula: (20 / 100) x 85 = 0.20 x 85 = 17. Answer: 17.
Example 2: 30 is what percent of 120?
Use formula: (30 / 120) x 100 = 0.25 x 100 = 25%. Answer: 25%.
Example 3: Change from 50 to 65
Use formula: (65 - 50) / 50 x 100 = 15 / 50 x 100 = 30% increase.
Common Mistakes to Avoid
Confusing "percent of" with "percent change." They use different formulas.
Using the wrong base when calculating percent change. Always divide by the original, not the new value.
Forgetting to multiply by 100 at the end. The fraction (Part/Whole) gives a decimal, not a percent.
Thinking 100% more means doubling the percentage. It means doubling the original number.
