How to Calculate Percentages in Python: Various Methods

Calculating percentages is very useful in many areas of life, including mathematics, finance, statistics, and data analysis. In the world of programming, being able to calculate percentages using Python can be useful for a wide range of applications. Whether you’re working with financial data, analyzing survey results, or creating interactive visualizations. In this tutorial, you will understand how to calculate percentages in Python. After knowing it you will know why it is a powerful tool to work with.

In this tutorial, we will explore the basics of calculating percentages in Python, including the different formulas and built-in functions available. We will also provide practical examples and exercises to help solidify your understanding and give you hands-on experience.

Understanding the Basics

What is a Percentage?

Before diving into the calculations, let’s start by understanding what a percentage is. A percentage is a way of expressing a fraction or a part of a whole as a proportion out of 100. For example, 50% represents half of something, while 75% represents three-fourths of something. In Python, percentages are represented using the “%” symbol, which is commonly referred to as the modulus operator.

Formulae for Percentage Calculation

Calculate the Percentage of a Value

One common scenario where percentage calculations are useful is when determining the sales tax on a purchase. To calculate the percentage of a value, you can use the formula, percentage = (part/whole) * 100. Let’s say you want to calculate the sales tax on a $100 purchase where the tax rate is 8%. Using this formula, the calculation would be percentage = (8 / 100) * 100 = 8.0. In Python, you can implement this formula as follows:

purchase_amount = 100
tax_rate = 8
sales_tax = (tax_rate / 100) * purchase_amount

Calculate the Increase or Decrease Percentage

Calculating the increase or decrease percentage is useful when analyzing changes in values over time. For example, you may want to calculate the percentage increase in the price of a product from its original price to its current price. The formula for calculating the increase or decrease percentage is percentage = ((new_value – old_value) / old_value) * 100. Suppose the original price of a product was $50, and it increased to $60. Using this formula, the calculation would be percentage = ((60 – 50) / 50) * 100 = 20.0. In Python, you can calculate the percentage increase as follows:

original_price = 50
current_price = 60
percentage_increase = ((current_price - original_price) / original_price) * 100

Built-in Functions for Percentage Calculation in Python

Using the “round” Function for Precision Control

When working with percentages, it is often necessary to round off the calculated values for enhanced readability and accuracy. Python provides a built-in function called “round” that can be used to control the precision of decimal numbers. For example, if you calculated a percentage as 25.555555, you can use the “round” function to round it to 25.56 for better presentation.

percentage = 25.555555
rounded_percentage = round(percentage, 2)

Formatting Percentages with String Formatting Techniques

Using the “%” Operator Method (Older Method)

In older versions of Python, the “%” operator was used for string formatting, including formatting percentages. This method involves using placeholders in a string and specifying the desired precision. For example, to format a percentage with two decimal places, you can use the “%f” placeholder followed by the “%” symbol.

percentage = 25.555555
formatted_percentage = "%.2f%%" % percentage

Using the “format” Method

In newer versions of Python, the “format” method is the preferred way of formatting strings, including percentages. This method provides more flexibility and readability. To format a percentage using the “format” method, you can use the “{:.2f}%” format specifier, where “:.2f” specifies two decimal places.

percentage = 25.555555
formatted_percentage = "{:.2f}%".format(percentage)

Practical Examples and Exercises

Percentage Calculation in Real-World Scenarios

To demonstrate the practical applications of percentage calculations in Python, let’s explore a few real-world scenarios:

Grade Calculation

Suppose you have a list of students’ test scores and you want to calculate their grades based on a predefined grading scale. You can calculate the percentage score for each student and assign a grade based on the percentage achieved.

test_scores = [85, 92, 78, 95, 88]
maximum_score = 100

for score in test_scores:
  percentage = (score / maximum_score) * 100
    if percentage >= 90:
        grade = "A"
    elif percentage >= 80:
        grade = "B"
    elif percentage >= 70:
        grade = "C"
    elif percentage >= 60:
        grade = "D"
        grade = "F"
print(f"Percentage: {percentage:.2f}%, Grade: {grade}")

Data Analysis

When working with data analysis, you may need to calculate the percentage of occurrences of certain events. For example, you may want to calculate the percentage of customers who made a purchase out of the total number of website visitors.

total_visitors = 1000
purchases = 350
conversion_rate = (purchases / total_visitors) * 100
print(f"Conversion Rate: {conversion_rate:.2f}%")


In this beginner’s guide, we have explored the basics of calculating percentages in Python. We covered the different formulas for calculating the percentage of a value and the increase or decrease percentage. We also discussed the built-in functions, such as the “round” function, and the string formatting techniques for formatting percentages.

By mastering the art of percentage calculations in Python, you have acquired a valuable skill that can be applied to various real-life scenarios, from financial calculations to statistical analysis. Remember to practice and experiment with different scenarios to enhance your understanding. Python offers endless possibilities, and percentages are just the beginning.

We encourage you to explore further by implementing percentage calculations in your own projects. As you delve deeper into Python programming, you will discover new ways to leverage the power of percentages. If you’re interested in diving deeper into Python and its capabilities, there are many online resources and references available to help you on your journey.

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