If current date is less than a recurring monthly payment date

Hi,

II'm trying to set up a home budget tracker but am having problem with the logic around reoccurring monthly direct debits. In plain English here's what I'm trying to achieve.

if current day of month is less than day of month direct debit then next direct debit date = current month + direct debit day of month else next direct debit date = Next month + the direct debit day of month.

For example if

Mortgage payment goes out on the 19th of each month and today is the 7th

If 7 < 19 then next mortgage payment = 1st date of current month(01/09/2013) + 19 else 1st Date of Next Month (01/10/2013)+ 19

I think the problem I am having is retrieving the 1st day of the month e.g 1st Sept rather than just the month expressed as a numeral?

thaks