An Excel spreadsheet is a document used to keep track of finances, contacts and other types of numerical data. When keeping track of data, the user often inserts a date. Excel has data functions and formulas to add or subtract days, months or years. One of these functions is the "Day()" function, which is used to calculate the day in a specific date.
Open the Excel spreadsheet you want to edit. You can also create a new spreadsheet to test the date formulas. When you start Excel from the Windows Start menu, a new spreadsheet is automatically created.
Enter a date into the first cell labeled "A1." This can be any date of the year even if it's the last day of the month or year. When you add a day to the date, Excel automatically transitions the date to the following month or year.
Use the "Day()" formula to add to the days. Enter the new formula in a cell adjacent to the A1 cell. The following code adds 10 days to the date in the A1 cell:
=date(year(a1), month(a1), day(a1) + 10)
The equal sign indicates a formula is entered, and it is required by Excel. The "date()" function turns the year, day and month into a full date string.
View the results of the formula. Notice that there are 10 days added to the date in the A1 cell. Additionally, if you change the date in the A1 cell, the formula updates and reflects the changes.