There is a SQL Server T-SQL function that calculates the number of days (or months, or years, or other time periods) between any two dates.
SELECT DATEDIFF(day, 'firstdate', 'seconddate');
But I regularly get asked how to work out the number of days between two dates, excluding the weekends (Saturday and Sunday).
I've seen a few functions around that do a pretty good job at this but many don't work properly if you have DATEFIRST changed in your session ie: if you change the first day of the week.
So I added a tool to SDU Tools to calculate this, and ensuring that the DATEFIRST setting doesn't cause it issues. You can use it like this:
SELECT SDU_Tools.DateDiffNoWeekends('firstdate', 'seconddate');
You can see it in action here:
You can find out more about our free SDU Tools here: