How to Calculate Percentage: 3 Methods Anyone Can Learn

The word "percent" originates from the Latin per centum, which literally translates to "by the hundred." When you see a percentage like 25%, it represents a ratio of 25 out of 100, or the fraction 25/100 (which simplifies to 1/4 or the decimal 0.25).

Percentages are incredibly versatile because they provide a standardized way to compare proportions. However, many people struggle with percentages because they are taught to memorize formulas without understanding the underlying math. In this guide, we break down percentage math into three simple, intuitive methods that cover virtually every everyday scenario.

Method 1: Finding the Percentage of a Number

This is the most common percentage calculation. It answers questions like: "What is 15% of $80?" or "How much is 8% sales tax on a $50 purchase?"

To calculate this, convert the percentage into a decimal (by dividing by 100) and multiply by the base number:

Let's work through an example: Find 15% of $80.

• Convert 15% to a decimal: `15 ÷ 100 = 0.15`.
• Multiply by the base number: `0.15 × $80 = $12.00`.

Mental Math Shortcut: To calculate percentages in your head, start by finding 10%. To find 10% of any number, simply move the decimal point one place to the left. For $80, 10% is $8. To find 5%, take half of the 10% amount ($4). Add them together to find 15%: `$8 + $4 = $12`. This simple trick works for many common percentages (like doubling 10% to find 20%).

Method 2: Finding What Percentage One Number is of Another

This method answers questions like: "25 is what percent of 200?" or "If I scored 42 out of 50 on an exam, what is my percentage grade?"

To calculate this, divide the part by the whole, and then multiply by 100 to convert the decimal into a percentage:

Let's work through the exam example: 42 out of 50.

• Identify the part and the whole: Part = 42, Whole = 50.
• Divide: `42 ÷ 50 = 0.84`.
• Multiply by 100: `0.84 × 100 = 84%`.

Method 3: Calculating Percentage Change (Increase or Decrease)

This method is used in business, finance, and economics to measure growth or decline over time. It answers questions like: "If my salary rose from $50,000 to $55,000, what is the percentage raise?" or "If a stock dropped from $100 to $85, what is the loss percentage?"

To calculate percentage change, subtract the original value from the new value to find the change amount, divide the change by the original value, and multiply by 100:

Let's work through the salary raise example:

• Subtract original from new: `$55,000 − $50,000 = $5,000` (positive change represents an increase).
• Divide the change by the original value: `$5,000 ÷ $50,000 = 0.10`.
• Multiply by 100 to get the percentage: `0.10 × 100 = 10%`.

If the result is negative (such as the stock drop: `(($85 − $100) ÷ $100) × 100 = −15%`), it indicates a percentage decrease.

Frequently Asked Questions