How to Calculate Percentage Increase and Decrease

Calculating how much something goes up or down in price can be easy if you follow these simple steps.

1. Percentage Increase

To find out how much something has increased in price, you can use this formula:

[ \text{Percentage Increase} = \left( \frac{\text{New Price} - \text{Old Price}}{\text{Old Price}} \right) \times 100 ]

Example:

Let’s say a shirt costs £20, and now it costs £25.

First, figure out how much it went up:

• New Price: £25
• Old Price: £20
• Increase: £25 - £20 = £5

Now plug it into the formula:

[ \text{Percentage Increase} = \left( \frac{25 - 20}{20} \right) \times 100 = 25% ]

So, the shirt's price increased by 25%!

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2. Percentage Decrease

Now, let’s see how to find out how much something has decreased in price. Use this formula:

[ \text{Percentage Decrease} = \left( \frac{\text{Old Price} - \text{New Price}}{\text{Old Price}} \right) \times 100 ]

Example:

If the same shirt goes on sale for £15, we need to find out how much it decreased.

• Old Price: £20
• New Price: £15
• Decrease: £20 - £15 = £5

Now, use the formula:

[ \text{Percentage Decrease} = \left( \frac{20 - 15}{20} \right) \times 100 = 25% ]

So in this case, the shirt's price decreased by 25%!

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These formulas make it easy to see how much prices go up or down!