Click to explore updated revision resources for GCSE Maths: Increase or decrease an amount by a percentage, with step-by-step slideshows, quizzes, practice exam questions, and more!

To increase or decrease an amount by a percentage, first calculate the percentage of the amount and then either add this answer on to increase the quantity, or subtract this answer to decrease the quantity. There is more than one way to find the percentage of an amount.

Examples

Increase £50 by 8%.

Using the multiplying method, first find 8% of £50:

8% of £50 is £4, so to increase £50 by 8%, add the £4 onto the £50, which is £54.

Decrease 72 kg by 40%.

Using the 10% method, first find 40% of 72 kg:

40% of 72 kg is 28.8 kg, so to decrease 72 kg by 40%, subtract 28.8 from 72, which is 43.2 kg.

You can also use the multiplier method. This type of calculation is most convenient when used with a calculator but it is vital to use it when dealing with compound interest questions.

Firstly, consider what the overall percentage would be after the figure has had its percentage increase or decrease added or subtracted. Then convert this amount to a decimal, before finally multiplying by the number in question.

Examples

What is the multiplier for a 15% increase?

What is the multiplier for a 33% decrease?