In the example below column B shows travel expenses for the year and a yearly total using the SUM function. Now to convert them into percentage select the cells and press CTRLSHIFT. The excel formula for percentage is Portion Days Total Days 100.
The Grand Total will be at the end of the column and in a fixed cell.
Type the forward slash sign. This is a shortcut to convert number into percentage. In column C we want to know the percentage that each month contributed to the total. If you want to calculate a percentage of a number in Excel simply multiply the percentage value by the number that you want the percentage of.