First date of month + AX

If you want to get first date of month

TransDate AnyDate=systemDateget();
TransDate FirstdateOfMth; ;
FirstdateOfMth=mkdate(1,mthofyr(AnyDate),year(AnyDate));
info(date2str(FirstdateOfMth,123,2,2,2,2,4));

This is second method to get first day of month. DateStartMth is standard global method.

TransDate AnyDate=today();
TransDate FirstdateOfMth; ;
FirstdateOfMth=DateStartMth(AnyDate);
info(date2str(FirstdateOfMth,123,2,2,2,2,4));

Systemdateget and today method will give you current system date.