How to Calculate the Number of Days between Two Dates in Microsoft Excel

1. Open the Excel workbook with dates you want to work with.
2. Enter the first or starting date in an empty cell. For example, if you want to enter the first day of the billing cycle, you can enter that in cell A1. Make sure you enter the month, day and year. If you do not enter a year, Excel will default to the current year.
3. Enter the second or ending date in another empty cell, for example, cell B1.
4. Highlight both cells and click the number format window in the 'Number' group on the ribbon. Select 'Short Date' or 'Long Date' from the menu, depending on how you want the dates displayed. The number format window typically displays the word 'General' initially, but it can display 'Custom' or any of the other formats. Excel generally recognizes dates when they are entered in date format; however, it is always useful to make sure your cells are formatted as dates.
5. Click an adjacent cell such as C1 to enter your formula. Type the following formula, substituting your own cell numbers for 'B1' and 'A1,' and press 'Enter':=B1-A1Excel will subtract one date from the other and display the number of days between the two dates.