How to Calculate Percentages: Formulas & Examples

What is a percentage?

A percentage is just a fraction out of 100. "20%" means 20 per 100, or 0.20 as a decimal. To turn a percentage into a decimal, divide by 100; to turn a decimal into a percentage, multiply by 100.

Finding a percentage of a number

This is the most common case — for example, "what is 15% of 200?". The formula is: result = (percentage ÷ 100) × value.

So 15% of 200 = 0.15 × 200 = 30. You can compute any case this way; the Percentage Calculator does it instantly as you type.

Percentage change (increase or decrease)

To measure how much a value went up or down in percentage terms, use: change % = (new − old) ÷ old × 100.

Example: a price rises from 80 to 100. Change = (100 − 80) ÷ 80 × 100 = 25%, an increase. If it dropped from 200 to 150, that is a 25% decrease. The Percentage Change Calculator handles both directions.

Working out a discount

A discount is a percentage taken off a price: final price = price × (1 − discount ÷ 100).

A $120 item at 25% off costs 120 × 0.75 = $90, saving $30. The Discount Calculator shows the final price and the savings together.

Common mistakes to avoid

• A 50% increase followed by a 50% decrease does not return the original number (100 → 150 → 75).
• Percentage points are not percentages: going from 10% to 12% is a 2 percentage-point rise, but a 20% relative increase.
• Always be clear what the percentage is "of" — the base matters.