How to calculate percentage of a number

Posted on

Calculating percentages of a number is a fundamental mathematical skill that is used in various real-life situations, from calculating discounts during shopping to determining tax amounts or understanding statistical data. Whether you're a student learning basic arithmetic or an adult managing finances, understanding how to calculate percentages is essential for making informed decisions and interpreting numerical information accurately. In this comprehensive guide, we'll explore the concept of percentages, different methods for calculating percentages of a number, and practical examples to illustrate their application in everyday scenarios.

Understanding Percentages

Before delving into the calculation methods, it's important to grasp the concept of percentages. A percentage is a way of expressing a fraction or ratio as a fraction of 100. It represents a proportion or share of a whole, where 100% represents the entire quantity or value. For example, if you receive a score of 80% on a test, it means you answered 80 out of 100 questions correctly, or 80% of the total possible score.

Basic Percentage Calculation

The most straightforward method for calculating a percentage of a number is through the formula:

Percentage = (Part / Whole) * 100


  • Percentage is the percentage value you want to find.
  • Part is the part of the whole that you're interested in (e.g., the discount amount, tax rate, etc.).
  • Whole is the total quantity or value.


Suppose you want to calculate 20% of 150. Using the formula:

Percentage = (20 / 100) * 150 = 0.20 * 150 = 30

So, 20% of 150 is 30.

Percentage Increase or Decrease

In addition to calculating simple percentages, it's also important to understand how to calculate percentage increases or decreases relative to a base value. This is useful for understanding changes in quantities over time, such as changes in prices, populations, or test scores.

Percentage Increase

To calculate the percentage increase from an initial value to a final value, you can use the formula:

Percentage Increase = ((Final Value - Initial Value) / Initial Value) * 100

Percentage Decrease

Similarly, to calculate the percentage decrease from an initial value to a final value, you can use the formula:

Percentage Decrease = ((Initial Value - Final Value) / Initial Value) * 100


Suppose the price of a product increases from $50 to $60. To find the percentage increase:

Percentage Increase = ((60 - 50) / 50) * 100 = (10 / 50) * 100 = 20%

So, the price has increased by 20%.

Practical Examples

  1. Calculating Discounts: When shopping, retailers often offer discounts expressed as percentages. For instance, if a product is on sale for 25% off its original price of $80, you can calculate the discounted price using the appropriate formula.

  2. Tax Calculation: When calculating taxes, such as sales tax or income tax, percentages are used to determine the amount owed. For example, if the sales tax rate is 8% and you purchase an item for $100, the total cost including tax would be calculated accordingly.

  3. Understanding Statistics: Percentages are commonly used in statistical analysis to describe proportions or changes within a dataset. For instance, if a survey indicates that 60% of respondents prefer option A over option B, it provides valuable insights into the preferences of the population surveyed.

  4. Grade Calculation: In education, percentages are often used to represent grades or scores on assignments, exams, or overall performance. For example, if a student scores 85 out of 100 on a test, their grade can be expressed as 85%.

Tips for Accuracy

  • Use Decimals: When performing calculations involving percentages, it's often more accurate to use decimals rather than percentages. For example, 20% can be expressed as 0.20 in calculations.
  • Check Units: Ensure that the units of measurement are consistent throughout your calculations to avoid errors. For instance, if one quantity is in dollars and another in cents, convert them to the same unit before performing calculations.

In summary, understanding how to calculate percentages of a number is a valuable skill with numerous practical applications in everyday life. Whether calculating discounts, taxes, or analyzing statistical data, percentages provide a standardized way of expressing proportions and changes within a dataset. By mastering the basic principles and formulas for percentage calculation, individuals can make informed decisions and interpret numerical information accurately in various contexts.