Re: 1st day of previous month

A bit long winded,but gives the answer you need.  There probably is a better way of doing it.

=ToDate("01/"+(ToNumber(FormatDate(RelativeDate((ToDate("01/"+(ToNumber(FormatDate(CurrentDate();"MM")))+"/"+ToNumber(FormatDate(CurrentDate();"yy"));"dd/MM/yyyy"));-1);"MM")))+"/"+ToNumber(FormatDate(RelativeDate((ToDate("01/"+(ToNumber(FormatDate(CurrentDate();"MM")))+"/"+ToNumber(FormatDate(CurrentDate();"yy"));"dd/MM/yyyy"));-1);"yy"));"dd/MM/yyyy")