Calculate the Percentage Change

This activity is about finding percentage change.

These may seem a bit tricky, but there is an easy formula that we can use to work them out. 

Percentage change = (actual change ÷ original) x 100 

Here's how it works!

The cost of an average loaf of bread was £1.06 a year ago. It is now £1.36.

Calculate the percentage increase in the cost of a loaf of bread.

We put our figures into the formula above:

Actual increase = £1.36 - £1.06 = 0.30

Percentage increase = 0.30 ÷ 1.06 x 100

Percentage increase = 0.28 x 100 = 28%

The cost of a loaf of bread has increased by 28%

We can use the same formula to work out a percentage decrease.

A computer game was priced at £15.49 last week. This week it has been reduced to £14.19. 

What is the percentage decrease?

Put the figures into our formula.

Actual decrease = £15.49 - £14.19 = £1.30

Percentage decrease = £1.30 ÷ £15.49 x 100

Percentage decrease = 0.08 x 100 = 8%

There was a percentage decrease of 8%

Let's try it out in a couple of questions.

Example 1

A metal bar increases its length from 2 m to 2.01 m after heating.

Find the percentage increase in its length.

Actual increase = 2.01 - 2 = 0.01 m

Percentage increase = (actual increase ÷ original length) x 100 = (0.01 ÷ 2) x 100 = 0.5%

Example 2

A woman reduced her weight from 80 kg to 63 kg after dieting.

Find the percentage decrease in her weight.

Actual decrease = 80 - 63 = 17 kg.

Percentage decrease = (actual decrease ÷ original weight) x 100 = (17 ÷ 80) x 100 = 21.25%

Just remember the formula for percentage change = (actual change ÷ original) x 100 

Let's try some questions now.