Percentage Calculator

Percentage formulas

Question	Formula	Example
What is X% of Y?	X ÷ 100 × Y	20% of 150 = 30
X is what % of Y?	X ÷ Y × 100	30 is 25% of 120
Percent change	(new − old) ÷ old × 100	80 → 100 is +25%
X is Y% of what?	X ÷ (Y ÷ 100)	30 is 20% of 150

Worked example

A price rises from $80 to $100. The change is 100 − 80 = 20, and 20 ÷ 80 × 100 = 25% increase. If it then falls back from $100 to $80, that is a 20 ÷ 100 = 20% decrease, because the starting value is now larger.

Quick mental math tips

• 10% of a number: move the decimal point one place left (10% of 64 = 6.4).
• 5% is half of 10%; 1% is a tenth of 10%.
• X% of Y equals Y% of X, so 8% of 50 is the same as 50% of 8, which is 4.
• To increase by a percentage, multiply by 1 + rate (a 15% rise is × 1.15).

Frequently asked questions

How do I calculate a percentage of a number?

Divide the percentage by 100 and multiply by the number. 15% of 80 is 0.15 × 80 = 12.

How do I find what percent one number is of another?

Divide the part by the whole and multiply by 100. 18 out of 24 is 18 ÷ 24 × 100 = 75%.

How do I calculate percent increase?

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

What is the difference between percent and percentage points?

A rate going from 4% to 5% rises 1 percentage point, which is a 25% increase in the rate itself.