When you want to know the number of days between two dates whether the date is in the future or the past, you can use Excel to calculate it.

The DAYS function in Microsoft Excel returns the number of days between two dates. The formula for the DAYS (end_date, start_date).

Microsoft Word has a date field, but it's not easy to use in an expression. If you need to update dates in a document, use Excel to calculate the dates and then run a mail merge.