Select the cell in which you entered 10. To calculate the difference as a percentage we subtract this months value from last months and then divide the result by last months value. The percentage of change between the two years is 23.
Excel offers us multiple configuration options.
The value is now formatted as a percentage with only one decimal place displayed. It has the default general formatting. After that hit OK and your decimals will be converted to percentages. To calculate the percentage of a number you just have to insert a number and apply the percentage.