You already know that when you select a cell with a date and drag the Auto Fill handle, Excel creates a series of sequential dates by adding one day each time. Did you know that you can control how many days are added?

A list of all the Mondays until December

1. Type two dates in two cells and select them. In this exemple, both dates are 7 days apart.
2. Drag the Auto Fill handle. Excel creates a series of dates 7 days apart, as it identified the first dates to be.
   
3. When you release the Auto Fill handle, the series of dates has been created.
     

Video: Use Auto Fill with Dates (41 seconds)