Calculating the percentage change from two numbers is a very common math problem to solve. In this blog post, we'll cover how to calculate the percentage difference from 4 to 21 and also check whether it is a percentage increase or a decrease.

Looking for percentage worksheets? Click here to see all of our free percentages worksheets.

There are a couple of simple steps we need to follow to find out the percentage change between 4 to 21. First of all, we need to deduct the number we want to measure the change from, 4 from the number we want to measure the change to, 21:

Now that we have the number 17, we can work out the decimal change by dividing it by the number we want to measure the change from, 4:

The final step in working out the change from 4 to 21 is to multiply our decimal number by 100. Remember that "percent" means parts per hundred, and this is why we have to multiply it by 100 to get our answer:

(Note that we have rounded the final percentage down to two decimal places)

As you can see, the actual process of calculating the percentage change from 4 to 21 is relatively straightforward to do. We can now easily see that the **percentage change from 4 to 21 is an increase of 425%**.

## Why Calculate a Percentage Change?

Percentages are very useful to make calculations easier and to understand numbers and the differences between them. It's much simpler to work with and understand parts of 100 than it is to use fractions that often do not have an exact, non-recurring, decimal equivalent.

Since a percentage is really just a fraction where the denominator is 100, comparisons are easier too.

For a percentage change, like from 4 to 21, we do these types of calculation all the time in real life. A few examples might be:

- A business might want to calculate whether their profit margin is increasing or decreasing
- An employee who worked extra hours this month might be curious to find out how much extra work he did as a percentage
- An investor looking at their portfolio might want to work out whether their investments have increased or decreased

## Practice Percentage Worksheets

Like most math problems, percentages is something that will get much easier for you the more you practice the problems and the more you practice, the more you understand.

Whether you are a student, a parent, or a teacher, you can create your own percentage worksheets using our percentages worksheet generator. This completely free tool will let you create completely randomized, differentiated, percentage problems to help you with your learning and understanding of percentages.

## Practice Percentage Changes Using Examples

If you want to continue learning about how to calculate a change in percentage between two numbers, take a look at the random calculations in the sidebar to the right of this blog post.

We have listed some completely random percentage change examples that you can follow along with to help you work through a number of problems.

Each article will show you, step-by-step, how to work out the percentage increase or decrease and will help students to really learn and understand this process.

## Calculate Another Percentage Difference

Enter your numbers into the boxes below below and click "Calculate" to work out the percentage increase or decrease.