How to Calculate Percentages (Three Ways That Cover Everything)

"How to calculate percentage" is one of the most-Googled maths queries every year. The three formulas below cover almost every situation.

1. X% of Y

Multiply the percent (as a decimal) by Y.

• 25% of 200 = 0.25 × 200 = 50
• 8% of 4500 = 0.08 × 4500 = 360

This is the everyday percentage. Sales tax, tips, exam scores out of total marks.

2. X is what % of Y?

Divide X by Y, multiply by 100.

• 17 is what % of 50? → 17 ÷ 50 × 100 = 34%
• 9 is what % of 60? → 9 ÷ 60 × 100 = 15%

This is for converting raw scores to percentages. Useful for grade calculation.

3. % change from A to B

Subtract A from B, divide by A, multiply by 100.

• From 80 to 92: (92 - 80) / 80 × 100 = 15% increase
• From 200 to 150: (150 - 200) / 200 × 100 = -25%, i.e. 25% decrease

This is for tracking change over time. Population growth, income growth, exam improvement.

Quick sanity checks

• 100% of something is the whole thing
• 50% is half
• 25% is a quarter
• 10% is moving the decimal one place left
• 1% is moving it two places left

Use those for ballpark estimates before computing exactly.

Try them on the calculator hub

Open Calculators and pick the Percentage tab. All three formulas, side by side.