Date functions:
The current month:
DateSerial(Year(Date()), Month(Date()), 1)
The next month:
DateSerial(Year(Date()), Month(Date()) + 1, 1)
The last day of the current month:
DateSerial(Year(Date()), Month(Date()) + 1, 0)
The last day of the next month:
DateSerial(Year(Date()), Month(Date()) + 2, 0)
The first day of the previous month:
DateSerial(Year(Date()), Month(Date())-1,1)
The last day of the previous month:
DateSerial(Year(Date()), Month(Date()),0)
The first day of the current quarter:
DateSerial(Year(Date()), Int((Month(Date()) - 1) / 3) * 3 + 1, 1)
The last day of the current quarter:
DateSerial(Year(Date()), Int((Month(Date()) - 1) / 3) * 3 + 4, 0)
The first day of the current week (assuming Sunday = day 1):
Date() - WeekDay(Date()) + 1
The last day of the current week:
Date() - WeekDay(Date()) + 7
The first day of the current week (using settings in Options dialog box):
Date() - WeekDay(Date(), 0) + 1
The last day of the current week:
Date() - WeekDay(Date(), 0) + 7