Percentage Increase or Decrease
Calculating percentage change is an important skill for geographers to have. When geographers collect data over a period of time, the results may increase. Calculating a percentage increase allows a geographer to see how much their data has changed.
Calculating the percentage increase between two figures is achieved by:
- calculate the difference between the two numbers
- divide the increase (difference) by the first number
- multiply the answer by 100.
In this example, we will examine changes in the GDP for the UK. In 2001 the UK had a total economic output of £1.3 trillion. In 2015 it was £1.64 trillion.
Therefore: 1.64 – 1.3 = 0.34 divided by 1.3 × 100 = 26.2% The UK total economic output between 2001 and 2015 had a percentage increase of 26.2%.
If the change between two numbers shows a decrease you need to:
- work out the difference between the two numbers being compared
- divide the decrease by the original number and multiply the answer by 100
- in summary: percentage decrease = decrease ÷ original number × 100
For example, the number of foxes in an area of woodland in February and March is counted. In February 22 foxes were counted. In March 12 foxes were counted. What is the percentage decrease of foxes in the woodland?
- the difference between the two numbers is 10
- 10 ÷ 22 × 100 = 45.4
- the percentage decrease of foxes found in the woodland is: 45.4%