How to Calculate Percentages

This calculator handles the three most common percentage calculations: finding a percentage of a number, finding what percentage one number is of another, and calculating percentage change between two values.

What is X% of Y?

Multiply the number by the percentage divided by 100. Example: 20% of $150 = $150 x 0.20 = $30. Quick trick: move the decimal two places left. 15% of 200 = 200 x 0.15 = 30.

X is What Percent of Y?

Divide X by Y, then multiply by 100. Example: 25 is what % of 200? Answer: (25/200) x 100 = 12.5%. This is useful for calculating grades, discounts, or commission rates.

Percentage Change

The formula is: ((New - Old) / Old) x 100. If a stock goes from $80 to $100: ((100-80)/80) x 100 = 25% increase. If it drops to $60: ((60-80)/80) x 100 = -25% decrease.

Frequently Asked Questions

What is 20% of 100?

20% of 100 = 20. Multiply 100 x 0.20 = 20.

How do I calculate a percentage in my head?

For 10%: move the decimal one place left. For 5%: find 10% then halve it. For 20%: find 10% then double it. For 15%: find 10% + 5%.

What is percentage change vs percentage difference?

Percentage change measures change from an original value: ((new-old)/old)x100. Percentage difference compares two values without a baseline: ((|a-b|)/((a+b)/2))x100.

How do I find the original price before a discount?

Divide the sale price by (1 - discount rate). Example: Item costs $80 after 20% off. Original = $80 / 0.80 = $100.