CFLib.org – Common Function Library Project

Description:
LastDayOfMonth() takes your selected month as a number (1-12) and an optional given year (which is good for instances of a Leap Year). It returns a date object that you can then use DateFormat to get the appropriate format for the month, day, and year.

Return Values:
Returns a date object.

Example:

<cfset month = 2>
<cfset year = 2004>

last day of the month is: 
<cfoutput>#LastDayOfMonth(month, year)#</cfoutput>
<br>- or -<br>
last day of the month is: 
<cfoutput>#DateFormat(LastDayOfMonth(month, year), "dddd mmm dd, yyyy")#</cfoutput>

Parameters:

Full UDF Source:

/**
 * Returns a date object representing the last day of the given month.
 * 
 * @param strMonth      Month you want to get the last day for, (Required)
 * @param strYear      Year for the specified month.  Useful for leap years.  The default is the current year. (Optional)
 * @return Returns a date object. 
 * @author Ryan Kime (ryan.kime@somnio.com) 
 * @version 1, May 7, 2002 
 */
function LastDayOfMonth(strMonth) {
  var strYear=Year(Now());
  if (ArrayLen(Arguments) gt 1)
    strYear=Arguments[2];
  return DateAdd("d", -1, DateAdd("m", 1, CreateDate(strYear, strMonth, 1)));
}