Percentage Calculator
Three questions, one page: What is X% of Y? X is what percent of Y? And what is the percentage change from X to Y? Type two numbers and the answer updates as you type — tips, taxes, discounts, grade averages and growth rates all come down to these three formulas.
What is X% of Y?
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X is what percent of Y?
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% change from X to Y
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The three percentage formulas
Percent just means "per hundred", so 20% of 150 is 20 ÷ 100 × 150 = 30. To find what share one number is of another, divide and multiply by 100: 45 of 90 → 45 ÷ 90 × 100 = 50%. For percentage change, take the difference and divide by the original value: a price going from 80 to 100 changed by (100 − 80) ÷ 80 × 100 = +25% — a common mistake is dividing by the new value instead.
FAQ
- Why is the percent change different from +25% to −25%?
- Because the denominator changes. 80 → 100 is +25% of 80, but 100 → 80 is −20% of 100. Percentage change always divides by the starting value.
- Does this page upload my numbers?
- No. Every calculation runs in the JavaScript on this page; nothing is sent anywhere.
- Can I use decimals and negative numbers?
- Yes — 2.5, 0.75 and −15 all work in every field.