How to Calculate Percentage: Formula and Examples
Learn the simple mathematical formulas for calculating percentages, percentage changes, and ratios with clear, easy-to-understand examples.
Mathematics & Applied Science Specialists
What is a Percentage?
A percentage is a number or ratio expressed as a fraction of 100. It is often denoted using the percent sign, "%". For example, 45% (read as "forty-five percent") is equal to 45 / 100, or 0.45.
The Basic Percentage Formula
To find the percentage of a number, use this formula: Percentage = (Value / Total Value) × 100
Example: What percentage is 20 out of 50?
- Divide the value (20) by the total (50): 20 ÷ 50 = 0.4
- Multiply by 100: 0.4 × 100 = 40
- Answer: 40%
Percentage Change Formula (Increase or Decrease)
To find the percentage increase or decrease between two numbers: Percentage Change = [(New Value - Old Value) / |Old Value|] × 100
Example: A price increases from $40 to $50. What is the percentage increase?
- Difference: 50 - 40 = 10
- Divide by old value: 10 ÷ 40 = 0.25
- Multiply by 100: 25% Increase
Compute Online Instantly
To calculate percentage increases, discounts, or ratios right now without manual math, try our interactive free Percentage Calculator.
Frequently Asked Questions
How do I calculate 20% of a number quickly?
To find 20% quickly, simply divide the number by 5. For example, 20% of 80 is 80 ÷ 5 = 16. Alternatively, find 10% by moving the decimal one place to the left (8.0), and double it (16).