Some basic examples of how to calculate percentages using Excel formulas.

**Percentages as a proportion**

The formula in D3 is:

*=B3/C3*

**Calculate percentages backwards to find a starting value**

The formula in D3 is:

*=B3/(1+C3)*

**Percentage increases and decreases**

The formula in D3 is:

*=(C3-B3)/C3*

Although both differences are based on the same two values, the % difference differs because the calculation is always the increase divided by the original value.

As well as knowing how to make the calculations in Excel, its important to thoroughly understand how percentages actually work. For example, if something priced at £100 is discounted 25%, then a week later the price is increased by 25% what is the new price?

If you answered £100 you probably want to look at the below example:

This highlights the fact that a 25% decrease followed by a 25% increase will not cancel each other out, because each calculation is based again on the original starting value.