Setting ToDate parameter

Hi All, Quick question, I'm looking to set my 'ToDate' parameter to the last day of the month up to 23:59:59 but can't figure it out.I've got my parameter to set the the final day of the month (using this: =DateSerial(Year(Now()), Month(Now()), "1").AddDays(-1)) but not up to a second before midnight, so infact it is missing out the final day of the months data.Many thanks.