Maths
Percentage Calculator
Handle the three percentage questions that come up constantly: what is X% of Y, X is what percent of Y, and the percentage change between two numbers.
Updated 16 Oct 2026
15% of 200 is 30.
Choose which kind of percentage question you have, enter the two numbers, and the calculator shows the answer along with the intermediate step so you can follow the working.
What is the Percentage Calculator?
A percentage expresses a number as a fraction of 100. Nearly every practical percentage question is one of three forms, and mixing them up is the usual source of error.
How to use the Percentage Calculator
- Pick the question type that matches what you are trying to find.
- Enter the two numbers.
The computation tape below the result shows the intermediate value, so you can check the working rather than trusting the output.
Formula
result = (X ÷ 100) × Y
X is what percent of Y?
result = (X ÷ Y) × 100
Percentage change from X to Y
result = ((Y − X) ÷ |X|) × 100
Percentage change divides by the starting value, not the ending one. Going from 50 to 75 is a 50% increase; going from 75 back to 50 is a 33.3% decrease. The same absolute change gives different percentages depending on direction, which surprises people constantly.
How the calculation works
Each form is a single arithmetic step once the percentage is converted to or from a decimal. The calculator shows that conversion explicitly so the logic is visible rather than hidden.
Worked example
15% of 200: 15 ÷ 100 = 0.15, then 0.15 × 200 = 30.
30 is what percent of 200: 30 ÷ 200 = 0.15, then × 100 = 15%.
Change from 200 to 230: difference is 30, then 30 ÷ 200 × 100 = 15% increase.
Uses and benefits
- Work out discounts, tips and tax shares in one step.
- Express a score or a share as a percentage.
- Measure growth or decline between two figures correctly.
Frequently asked questions
Subtract the original from the new value, divide by the original, then multiply by 100. From 200 to 230: (230 − 200) ÷ 200 × 100 = 15%. Always divide by the starting value.
Because the two percentages apply to different bases. 100 rises by 50% to 150; a 50% fall from 150 is 75, not 100. The second percentage is calculated on the larger number.
Divide the part by the whole and multiply by 100. If 30 out of 200 people responded, that is 30 ÷ 200 × 100 = 15%.
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