Percentage Calculator
What is X% of Y?
X is what percent of Y?
Percentage change from A to B
How it works
Pick one of three modes and the answer appears as you type: 'what is X% of Y' for discounts, tips, or VAT; 'X is what percentage of Y' for scores, completion, or share of a total; and 'percentage change from X to Y' for growth, markups, or price drops. Each mode is a separate, clearly labelled calculation, so you do not have to remember which formula to use. In change mode, a second value smaller than the first gives a negative result, showing a decrease, which is what you want for a price reduction or a drop in a metric. The tool covers shopping discounts, exam marks, statistics, finance, and everyday 'what percent is this' questions. All the math runs in your browser with no backend, so your numbers are processed locally inside the tab and are never transmitted anywhere.
Frequently Asked Questions
What calculation modes are available?
- Three modes: 'What is X% of Y', 'X is what % of Y', and 'Percentage change from X to Y'.
What is 15% of 200?
- 30. Multiply the whole by the percentage and divide by 100: 200 × 15 ÷ 100 = 30, or 200 × 0.15 = 30. Use the first mode, 'What is X% of Y', with X = 15 and Y = 200. The same shape covers a 15% tip on a 200 bill and 15% VAT on a 200 net price.
25 is what percent of 200?
- 12.5%. Divide the part by the whole and multiply by 100: 25 ÷ 200 = 0.125, so 12.5%. Use the second mode, 'X is what % of Y', with X = 25 and Y = 200. This is the mode for exam scores, completion rates and share of a total.
What is the percentage change from 80 to 100?
- +25%. Subtract, divide by the original value, then multiply by 100: (100 − 80) ÷ 80 = 0.25, so a 25% increase. The reverse is not −25%: from 100 back to 80 is (80 − 100) ÷ 100 = −20%. The base changes with the direction, which is why a 25% rise is undone by a 20% fall.
Can I calculate percentage decrease?
- Yes. If the second value is smaller than the first, the percentage change comes out negative, which is the decrease.
Is my data safe?
- Yes. The tool is a static client-side app with no backend. Your input is processed by JavaScript running inside your browser tab and is never transmitted anywhere. You can confirm by opening DevTools → Network: using the tool produces zero outbound HTTP requests.