About the Percentage
A percentage calculator finds what one number is as a share of another, or what a given share of a number comes to. It is the most-used calculation in everyday life — discounts, tips, tax, grades, interest, and statistics all reduce to the same operation on a base of one hundred.
The formula
Result = (percent / 100) · numberThe word "percent" means "per hundred", so 20 percent is simply the fraction 20/100, or 0.2. Multiplying by that fraction gives you that share of the original number.
How to use this calculator
- 1Enter your What is (%). The field starts at
20, which you can overwrite. - 2Enter your of. The field starts at
150, which you can overwrite. - 3Read the result straight away — it recalculates as you type, so there is no button to press. Use Share to copy a link that reopens the page with your exact numbers filled in.
Worked example
| Input | Value |
|---|---|
| What is (%) | 20 |
| of | 150 |
Result
Result: 30.00
Those are the values the page loads with, so you can reproduce this result yourself and then change one field at a time to see what drives the outcome.
Understanding your result
There are three questions percentages answer, and they are the same equation rearranged. What is 20 percent of 150? Multiply: 0.2 × 150 = 30. What percentage is 30 of 150? Divide: 30 ÷ 150 = 0.2, so 20 percent. And 30 is 20 percent of what? Divide again: 30 ÷ 0.2 = 150. Recognising which of the three you are being asked is most of the difficulty.
The trap is percentage change versus percentage points. A rate rising from 4 percent to 6 percent has risen by 2 percentage points, but by 50 percent in relative terms. Both statements are true and they describe the same event, which is why the distinction matters whenever the numbers themselves are already percentages.
Things worth knowing
- Percentage increases and decreases are not symmetric. A 50 percent rise followed by a 50 percent fall leaves you 25 percent below where you started.
- To add a percentage, multiply by 1 plus the decimal: a 15 percent tip is the bill × 1.15 in a single step.
- To find the original price before a discount, divide rather than multiply: 80 dollars after 20 percent off means 80 ÷ 0.8 = 100.
- Ten percent is easy to find by moving the decimal point one place, and most mental percentage arithmetic builds from there.
- Percentages of very small bases are unstable. A move from 1 to 2 cases is a 100 percent increase and usually means very little.
Frequently asked questions
How do I calculate a percentage of a number?+
Divide the percentage by 100 and multiply by the number. For 20 percent of 150, that is 0.2 × 150 = 30. Alternatively divide the number by 100 to get 1 percent, then multiply by the percentage you want.
How do I work out a percentage increase?+
Subtract the old value from the new one, divide by the old value, and multiply by 100. Going from 80 to 100 is (100 − 80) ÷ 80 × 100 = 25 percent. Always divide by the starting value, not the ending one.
What is the difference between percent and percentage points?+
Percentage points measure the absolute gap between two percentages; percent measures the relative change. A move from 4 to 6 percent is 2 percentage points, or a 50 percent increase.
How do I reverse a percentage discount?+
Divide rather than subtract. If an item cost 60 dollars after 25 percent off, the original was 60 ÷ 0.75 = 80 dollars. Subtracting 25 percent from 60 gives the wrong answer.