A Guide to Understanding and Calculating Percentages

Percentages are a fundamental part of everyday math, from calculating a tip at a restaurant to understanding financial reports. "Percent" literally means "per one hundred." It's a way of expressing a number as a fraction of 100. Our calculator simplifies these problems, but understanding the formulas can be incredibly helpful. Below, we break down each calculation type with examples.

1. How to Calculate a Percentage of a Number

This is the most common percentage calculation. It's used for finding discounts, sales tax, or a tip.

Formula: Result = (Percentage / 100) * Total Number

Example: What is 20% of $80?

Using the formula:
Result = (20 / 100) * 80
Result = 0.20 * 80 = 16
So, 20% of $80 is $16. If you're planning a major purchase, you might find our Loan & Mortgage Calculator useful for understanding the total cost.

2. How to Find What Percent One Number Is of Another

This calculation is useful for comparing a part to a whole. For example, finding what percentage of your monthly budget goes toward rent or what percentage of your answers on a test were correct.

Formula: Percentage = (Part / Whole) * 100

Example: 35 is what percent of 140?

Using the formula:
Percentage = (35 / 140) * 100
Percentage = 0.25 * 100 = 25%
So, 35 is 25% of 140. This type of calculation is common in health and fitness, such as determining body fat percentage, which you can explore in our Fitness & Health calculators.

3. How to Calculate Percentage Increase or Decrease

This is used to show how a value has changed over time. It's essential in finance to track investment performance, in business to track sales growth, or in science to measure change in experiments.

Formula: Percentage Change = ((New Value - Old Value) / Old Value) * 100

Example (Increase): What is the percentage increase from 200 to 250?

Using the formula:
Percentage Change = ((250 - 200) / 200) * 100
Percentage Change = (50 / 200) * 100 = 0.25 * 100 = 25% increase

Example (Decrease): What is the percentage decrease from 250 to 200?

Using the formula:
Percentage Change = ((200 - 250) / 250) * 100
Percentage Change = (-50 / 250) * 100 = -0.2 * 100 = -20% decrease
This calculation is a cornerstone of our financial calculators, helping users track their assets and liabilities.