If want to calculate percentage change in Excel, this can be done using a simple Excel formula.
Generally, if you have two numbers, a and b, the percentage change from a to b is given by the formula:
For example if your earnings are $1,250 in January and $1,750 in February, the percentage change in February, compared to January can be calculated in Excel by typing the following formula into any cell of your spreadsheet:
This gives the result 0.4, or +40%
As with any Excel formula, the percentage change calculation can use values that are stored in your spreadspeed, instead of actual numbers. This is shown in the spreadsheet below.
Formula:

Result:

Note that, by default, the result in cell B3 of the above spreadsheet will usually be displayed as the decimal 0.4. Therefore, if you want to display the result in cell B3 as the percentage 40%, you may need to apply percentage formatting to this cell.
The easiest way to format cells as percentages is to select the cell(s) to be formatted and then select the percentage button from the 'Number' group on the Home tab of the Excel ribbon (see below):
This uses the default percentage formatting style for your computer system which might be exactly what you require.
However, if you want to change the number of decimal places that are displayed, this can be done via the 'Format Cells' Dialog Box, which is brought up by clicking on the dialog box launcher (shown in the above image).
Within 'Format Cells' dialog box:
For further examples of Calculating Percentage Change in Excel, see the Microsoft Office website.
Or, for an overview of different types of percentage calculation, see the Percentages In Excel page.
When using the above percentage change formula, you may occasionally get the #DIV/0! error.
#DIV/0!   
Occurs if you attempt to divide by zero. I.e. if the value a in the formula (ba)/a is equal to zero. 