Showing the first and last day of the month

Use the DateSerial function

Using the Date Serial function, DateSerial(year,month,day), returning the first day of the month is straightforward:

<%
Dim first_day
first_day = DateSerial(Year(Date), Month(Date), 1)
%>

This returns: 01/12/2018

Returning the the last day of the month is the same as returning the day fefore the first day of next month.

<%
Dim last_day
last_day = DateSerial(Year(Date), Month(Date)+1, 1 - 1)
%>

This returns : 31/12/2018

This will work for any month - even February in a leap year!