Excel calculate: Calculating with dates

Excel calculate: Calculating with dates


Given the date on which an order was received and the number of days required to fulfill the order, you want to use Excel to calculate a delivery date. In this learning object, you will find out about how dates are managed in Excel and how to make calculations with them.


Values that represent dates are in reality stored as integer numbers. The earlierst date that Excel can process is January 1, 1900, which is represented internally by the number 1. All subsequent dates are represented by numbers that express the number of days that have elapsed since that initial day.


You can test this by entering the number 1 into a cell and then formating it as a date. You can also try this the other way around: enter today’s date, and then format it as a number.

Because dates are internally treated as numbers, you can easily make calculations with them. For example, you can use excel to calculate the difference between two dates, or add a certain number of days to any given date. In the following example, in cell B6, the date in cell B3 was added to the number in cell B4:

You can also subtract one date from another in order to determine how many days lie between them: