# Percentage calculator

Six everyday percentage sums, all on one page

Use it at https://www.quicktoolz.com/tools/percentage-calculator. From QuickToolz.

A percentage is a number out of 100. To find 20% of 150, divide 20 by 100 and multiply by 150, which gives 30. To find a percent change, divide the difference by the starting value. All six common sums are below, so just change the numbers in the one you need.

## How it works

part = percent ÷ 100 × whole

Every sum here is the same idea: part = percent ÷ 100 × whole. Each line rearranges that to find the missing number.

Worked example: 20% of 150 is 20 ÷ 100 × 150 = 30. To go from 100 to 125 is a change of (125 − 100) ÷ 100 = 25%.

## Examples

| Question | Answer |
| --- | --- |
| What is 15% of 80? | 12 |
| 45 is what percent of 60? | 75% |
| Change from 80 to 100 | 25% |
| 500 increased by 18% | 590 |

## What this tool doesn't cover

- Answers show up to two decimal places.

## Questions

### How do I work out a percent change?

Subtract the old value from the new one, divide by the old value, then multiply by 100.

### Why can’t I work out a change from 0?

It would mean dividing by zero, so there’s no meaningful answer.

### Is 10% more then 10% less the same number?

No. 100 plus 10% is 110, and 110 minus 10% is 99.

### How do I work out a percentage of a number?

Multiply the number by the percentage, then divide by 100. For example, 15% of 240 is 36.

### How do I work out what percentage one number is of another?

Divide the part by the whole, then multiply by 100. So 30 out of 120 is 25%.

## Sources

- [Khan Academy: percentages](https://www.khanacademy.org/math/cc-sixth-grade-math/cc-6th-arith-operations/cc-6th-percent-problems/a/percent-problems)