DocomintPercentage Calculator
Find X% of a number, calculate percentage change, or work out what percent one number is of another.
What is a Percentage Calculator?
Percentage questions come up in three different shapes that people often mix up: "what is X% of Y" (a discount, a tip, a tax), "what's the percentage change from A to B" (a price increase, a stat swinging quarter to quarter), and "X is what percent of Y" (test scores, market share). This bundles all three into one tool so you don't have to remember which formula goes with which question.
How to use the Percentage Calculator
- Pick which of the three percentage calculations you need
- Enter the numbers involved
- The result appears instantly, calculated on your device
Formula
X% of Y = (X ÷ 100) × Y | Change = ((B − A) ÷ A) × 100 | X is what % of Y = (X ÷ Y) × 100
Each of the three modes is a different rearrangement of the same relationship between a part, a whole, and a percentage — which one applies depends on which two of the three you already know.
Example
A shirt priced at $80 goes on sale for $104 — wait, that's an increase. Using the percentage-change mode on a $80 → $104 jump returns +30%, useful for checking a reported price hike against the actual before/after numbers rather than trusting a rounded headline figure.
Common mistakes
- Treating "percentage change" and "percentage points" as the same thing — a rate going from 20% to 25% is a 5-point increase, but a 25% percentage change.
- Reducing a value by 20% twice and assuming that's the same as a 40% reduction — the second 20% applies to a smaller base, so it isn't.
- Using "X is what % of Y" backward — dividing Y by X instead of X by Y gives the reciprocal, not the answer.
- Rounding an intermediate result before the final step, which compounds small errors across a multi-step calculation.
Frequently asked questions
How do I calculate X% of a number?
Divide the percentage by 100 to get a decimal, then multiply by the number. 15% of 240 is (15 ÷ 100) × 240 = 36.
What's the difference between percentage change and percentage points?
Percentage change is relative: going from 20% to 25% is a 5-percentage-point increase, but a 25% percentage change (5 is 25% of 20). News headlines often blur the two — always check which one a reported figure actually means.
How do I calculate a percentage decrease?
Use Percentage Change mode with the earlier value as "From" and the later, smaller value as "To" — the result comes back negative, e.g. a change from 100 to 80 returns −20%.
How do I convert a percentage to a decimal?
Divide by 100 — 15% becomes 0.15. This comes up when plugging a rate into another calculator (like Compound Interest) that expects a percentage rather than a raw fraction.
Is my numbers uploaded anywhere?
No — Percentage Calculator runs entirely in your browser using JavaScript/WebAssembly. Your numbers is never sent to a server.