Common date ranges using Active Support's date calculations

dates.rb

# require 'active_support'

# Monday, August 3, 2014

today = Date.today #=> Mon, 04 Aug 2014
Date.yesterday #=> Sun, 03 Aug 2014
Date.tomorrow #=> Tue, 05 Aug 2014

# this week
today.beginning_of_week #=> Mon, 04 Aug 2014
today.end_of_week #=> Sun, 10 Aug 2014

# last week
today.prev_week.beginning_of_week #=> Mon, 28 Jul 2014
today.prev_week.end_of_week #=> Sun, 03 Aug 2014

# this month
today.beginning_of_month #=> Fri, 01 Aug 2014
today.end_of_month #=> Sun, 31 Aug 2014

# last month
today.last_month.beginning_of_month #=> Tue, 01 Jul 2014
today.last_month.end_of_month #=> Thu, 31 Jul 2014

# 3 months ago
today - 3.months #=> Sun, 04 May 2014

# this quarter
today.beginning_of_quarter #=> Tue, 01 Jul 2014
today.end_of_quarter #=> Tue, 30 Sep 2014

# last quarter
today.prev_quarter.beginning_of_quarter #=> Tue, 01 Apr 2014
today.prev_quarter.end_of_quarter #=> Mon, 30 Jun 2014