Given A1 contains the starting date:
=DATE(YEAR(A1),MONTH(A1)+1,DAY(A1))
increments the month.
References
Adding/Subtracting n Month(s) To/From a Date, ozgrid.com
Excel forumula to add a month, Computing.Net
References
Adding/Subtracting n Month(s) To/From a Date, ozgrid.com
Excel forumula to add a month, Computing.Net