---
title: "Percentage calculator — free, runs in your browser"
description: "Work out a percentage of a number, what percent one number is of another, and percentage change. Free, no sign-up, and nothing you enter leaves your browser."
url: https://atoneplace.net/tools/percentage-calculator/
site: "At One Place"
---

# Percentage calculator

Work out a percentage of a number, what percent one number is of another, and percentage change.

## How it works

Three different questions get called "percentage" and they need different arithmetic, which is why they are separated here rather than crammed into one box.

What is X% of Y multiplies: 15% of 240 is 0.15 × 240 = 36. X is what percent of Y divides: 36 out of 240 is 36 ÷ 240 = 0.15, or 15%. Percentage change compares an old value to a new one: from 240 to 300 is (300 − 240) ÷ 240 = 25% up.

The one that catches people is that a percentage rise and the equivalent fall are not the same size. A price that goes up 50% and then falls 50% does not return to where it started — it ends 25% below, because the second percentage is taken from the larger number. This is also why a 50% discount followed by a further 20% off is 60% off in total, not 70%.

## Worked examples

*The three calculations, worked.*

| Question | Arithmetic | Answer |
| --- | --- | --- |
| What is 15% of 240? | 0.15 × 240 | 36 |
| 36 is what percent of 240? | 36 ÷ 240 × 100 | 15% |
| 240 to 300 is what change? | (300 − 240) ÷ 240 × 100 | +25% |
| 300 to 240 is what change? | (240 − 300) ÷ 300 × 100 | −20% |

> This tool runs entirely in your browser. Nothing you enter is sent to a server, logged or stored, and the page keeps working with the network disconnected.

## Common questions

### How do you calculate a percentage of a number?

Divide the percentage by 100 and multiply. For 15% of 240: 15 ÷ 100 = 0.15, then 0.15 × 240 = 36.

### Why is a 50% rise then a 50% fall not back to the start?

Because each percentage is taken from a different base. 100 rises by 50 to 150; 50% of 150 is 75, so it falls to 75 — a quarter below where it began.

### How do you add two discounts together?

You multiply what remains rather than adding the discounts. 50% off then 20% off leaves 0.5 × 0.8 = 0.4 of the price, which is 60% off in total, not 70%.

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