Percentage calculator

Percentages appear everywhere: discounts, tax, exam scores, growth figures, tips and statistics. This calculator handles the three most common questions so you do not have to remember which number to divide by which.

How to use it

1. Choose the question you want to answer.
2. Enter the two values.
3. Read the result.

The three core calculations

• What is X% of Y? Y × X / 100. 15% of 240 = 36.
• X is what percent of Y? X / Y × 100. 45 out of 60 = 75%.
• Percentage change from A to B: (B - A) / A × 100. From 80 to 100 = +25%; from 100 to 80 = -20%.

Common traps

• Increases and decreases are not symmetric. A 20% drop followed by a 20% rise does not return to the start: 100 becomes 80, then 96.
• Percent vs. percentage points. An interest rate rising from 4% to 5% is a 1 percentage point increase, but a 25% relative increase.
• Reverse percentages. If a price including 18% tax is 590, the pre-tax price is 590 / 1.18 = 500, not 590 minus 18% (483.80).
• Choose the right base. Percentage change always divides by the original value.

Mental math shortcuts

• 10% is the number divided by 10; 5% is half of that.
• X% of Y equals Y% of X: 8% of 50 is the same as 50% of 8, which is 4.