Numbers - date cell set to last day of the month
Might EOMONTH work for you?
The EOMONTH function returns a date that is the last day of the month some number of months before or after a given date.
Example: =EOMONTH("2/01/2015", 0) returns: Feb 28, 2015
Let us say the current date is in cell A192 and is 21 January 2017. You can insert the eomonth date in another cell with
eomonth(A192,0)