diff --git a/activesupport/CHANGELOG b/activesupport/CHANGELOG
index 09b69d3fbf..f93e8c28e0 100644
--- a/activesupport/CHANGELOG
+++ b/activesupport/CHANGELOG
@@ -1,3 +1,5 @@
+* Added Time::Calculations to ask for things like Time.now.tomorrow, Time.now.yesterday, Time.now.months_ago(4) #580 [DP|Flurin]
+
 * Upgraded to breakpoint 92 which fixes:
 
     * overload IRB.parse_opts(), fixes #443
diff --git a/activesupport/lib/active_support/core_ext/time.rb b/activesupport/lib/active_support/core_ext/time.rb
new file mode 100644
index 0000000000..e13cb07def
--- /dev/null
+++ b/activesupport/lib/active_support/core_ext/time.rb
@@ -0,0 +1,5 @@
+require File.dirname(__FILE__) + '/time/calculations'
+
+class Time#:nodoc:
+  include ActiveSupport::CoreExtensions::Time::Calculations
+end
diff --git a/activesupport/lib/active_support/core_ext/time/calculations.rb b/activesupport/lib/active_support/core_ext/time/calculations.rb
new file mode 100644
index 0000000000..f5e9ab212c
--- /dev/null
+++ b/activesupport/lib/active_support/core_ext/time/calculations.rb
@@ -0,0 +1,101 @@
+module ActiveSupport #:nodoc:
+  module CoreExtensions #:nodoc:
+    module Time #:nodoc:
+      # Enables the use of time calculations within Time itself
+      module Calculations
+        # Seconds since midnight: Time.now.seconds_since_midnight
+        def seconds_since_midnight
+          self.hour.hours + self.min.minutes + self.sec + (self.usec/1.0e+6)
+        end
+            
+        # Returns a new Time where one or more of the elements have been changed according to the +options+ parameter. The time options
+        # (hour, minute, sec, usec) reset cascadingly, so if only the hour is passed, then minute, sec, and usec is set to 0. If the hour and 
+        # minute is passed, then sec and usec is set to 0.
+        def change(options, time_factory_method = :local)
+          ::Time.send(
+            time_factory_method, 
+            options[:year]  || self.year, 
+            options[:month] || self.month, 
+            options[:mday]  || self.mday, 
+            options[:hour]  || self.hour, 
+            options[:min]   || (options[:hour] ? 0 : self.min),
+            options[:sec]   || ((options[:hour] || options[:min]) ? 0 : self.sec),
+            options[:usec]  || ((options[:hour] || options[:min] || options[:usec]) ? 0 : self.usec)
+          )
+        end
+
+        # Returns a new Time representing the time a number of seconds ago, this is basically a wrapper around the Numeric extension
+        # Do not use this method in combination with x.months, use months_ago instead!
+        def ago(seconds)
+          seconds.until(self)
+        end
+
+        # Returns a new Time representing the time a number of seconds since the instance time, this is basically a wrapper around 
+        #the Numeric extension. Do not use this method in combination with x.months, use months_since instead!
+        def since(seconds)
+          seconds.since(self)
+        end
+
+        # Returns a new Time representing the time a number of specified months ago
+        def months_ago(months, time_factory_method = :local)
+          if months >= self.month 
+            change({ :year => self.year - 1, :month => 12 }, time_factory_method).months_ago(months - self.month)
+          else
+            change({ :year => self.year, :month => self.month - months }, time_factory_method)
+          end
+        end
+
+        def months_since(months, time_factory_method = :local)
+          if months + self.month > 12
+            change({ :year => self.year + 1, :month => 1 }, time_factory_method).months_since(
+              months - (self.month == 1 ? 12 : (self.month + 1))
+            )
+          else
+            change({ :year => self.year, :month => self.month + months }, time_factory_method)
+          end
+        end
+
+        # Returns a new Time representing the "start" of this week (sunday, 0:00)
+        def beginning_of_week
+          (self - self.wday.days).midnight
+        end
+        alias :sunday :beginning_of_week
+        alias :at_beginning_of_week :beginning_of_week
+        
+        # Returns a new Time representing the start of the day (0:00)
+        def beginning_of_day
+          self - self.seconds_since_midnight
+        end
+        alias :midnight :beginning_of_day
+        alias :at_midnight :beginning_of_day
+        alias :at_beginning_of_day :beginning_of_day
+        
+        # Returns a new Time representing the start of the month (1st of the month, 0:00)
+        def beginning_of_month
+          self - ((self.mday-1).days + self.seconds_since_midnight)
+        end
+        alias :at_beginning_of_month :beginning_of_month
+        
+        # Convenience method which returns a new Time representing the time 1 day ago
+        def yesterday
+          self.ago(1.day)
+        end
+        
+        # Convenience method which returns a new Time representing the time 1 day since the instance time
+        def tomorrow
+          self.since(1.day)
+        end
+           
+        # Returns a new Time of the current day at 9:00 (am) in the morning
+        def in_the_morning(time_factory_method = :local)
+          change({:hour => 9}, time_factory_method)
+        end
+
+        # Returns a new Time of the current day at 14:00 in the afternoon
+        def in_the_afternoon(time_factory_method = :local)
+          change({:hour => 14}, time_factory_method)
+        end        
+      end
+    end
+  end
+end
\ No newline at end of file
diff --git a/activesupport/test/core_ext/time_ext_test.rb b/activesupport/test/core_ext/time_ext_test.rb
new file mode 100644
index 0000000000..ecad949c94
--- /dev/null
+++ b/activesupport/test/core_ext/time_ext_test.rb
@@ -0,0 +1,84 @@
+require 'test/unit'
+require File.dirname(__FILE__) + '/../../lib/active_support/core_ext/numeric'
+require File.dirname(__FILE__) + '/../../lib/active_support/core_ext/time'
+
+class TimeExtCalculationsTest < Test::Unit::TestCase
+  def test_seconds_since_midnight
+    assert_equal 1,Time.local(2005,1,1,0,0,1).seconds_since_midnight
+    assert_equal 60,Time.local(2005,1,1,0,1,0).seconds_since_midnight
+    assert_equal 3660,Time.local(2005,1,1,1,1,0).seconds_since_midnight
+    assert_equal 86399,Time.local(2005,1,1,23,59,59).seconds_since_midnight
+    assert_equal 60.00001,Time.local(2005,1,1,0,1,0,10).seconds_since_midnight
+  end
+
+  def test_begining_of_week
+    assert_equal Time.local(2005,1,30), Time.local(2005,2,4,10,10,10).beginning_of_week
+  end
+  
+  def test_beginning_of_day
+    assert_equal Time.local(2005,2,4,0,0,0), Time.local(2005,2,4,10,10,10).beginning_of_day
+  end
+  
+  def test_beginning_of_month
+    assert_equal Time.local(2005,2,1,0,0,0), Time.local(2005,2,22,10,10,10).beginning_of_month
+  end
+    
+  def test_months_ago
+    assert_equal Time.local(2005,5,5,10),  Time.local(2005,6,5,10,0,0).months_ago(1)
+    assert_equal Time.local(2004,11,5,10), Time.local(2005,6,5,10,0,0).months_ago(7)
+    assert_equal Time.local(2004,12,5,10), Time.local(2005,6,5,10,0,0).months_ago(6)
+    assert_equal Time.local(2004,6,5,10),  Time.local(2005,6,5,10,0,0).months_ago(12)
+    assert_equal Time.local(2003,6,5,10),  Time.local(2005,6,5,10,0,0).months_ago(24)
+  end
+
+  def test_months_since
+    assert_equal Time.local(2005,7,5,10),  Time.local(2005,6,5,10,0,0).months_since(1)
+    assert_equal Time.local(2005,12,5,10), Time.local(2005,6,5,10,0,0).months_since(6)
+    assert_equal Time.local(2006,1,5,10),  Time.local(2005,6,5,10,0,0).months_since(7)
+    assert_equal Time.local(2006,6,5,10),  Time.local(2005,6,5,10,0,0).months_since(12)
+    assert_equal Time.local(2007,6,5,10),  Time.local(2005,6,5,10,0,0).months_since(24)
+  end
+
+  def test_ago
+    assert_equal Time.local(2005,2,22,10,10,9),  Time.local(2005,2,22,10,10,10).ago(1)
+    assert_equal Time.local(2005,2,22,9,10,10),  Time.local(2005,2,22,10,10,10).ago(3600)
+    assert_equal Time.local(2005,2,20,10,10,10), Time.local(2005,2,22,10,10,10).ago(86400*2)
+    assert_equal Time.local(2005,2,20,9,9,45),   Time.local(2005,2,22,10,10,10).ago(86400*2 + 3600 + 25)
+  end 
+  
+  def test_since
+    assert_equal Time.local(2005,2,22,10,10,11), Time.local(2005,2,22,10,10,10).since(1)
+    assert_equal Time.local(2005,2,22,11,10,10), Time.local(2005,2,22,10,10,10).since(3600)
+    assert_equal Time.local(2005,2,24,10,10,10), Time.local(2005,2,22,10,10,10).since(86400*2)
+    assert_equal Time.local(2005,2,24,11,10,35), Time.local(2005,2,22,10,10,10).since(86400*2 + 3600 + 25)
+  end
+
+  def test_yesterday
+    assert_equal Time.local(2005,2,21,10,10,10), Time.local(2005,2,22,10,10,10).yesterday
+    assert_equal Time.local(2005,2,28,10,10,10), Time.local(2005,3,2,10,10,10).yesterday.yesterday
+  end
+  
+  def test_tomorrow
+    assert_equal Time.local(2005,2,23,10,10,10), Time.local(2005,2,22,10,10,10).tomorrow
+    assert_equal Time.local(2005,3,2,10,10,10),  Time.local(2005,2,28,10,10,10).tomorrow.tomorrow
+  end
+
+  def test_in_the_morning
+    assert_equal Time.local(2005,2,22,9), Time.local(2005,2,22,15,15,10).in_the_morning
+    assert_equal Time.local(2005,2,22,9), Time.local(2005,2,22,3,15,10).in_the_morning
+  end
+
+  def test_in_the_morning
+    assert_equal Time.local(2005,2,22,14), Time.local(2005,2,22,15,15,10).in_the_afternoon
+    assert_equal Time.local(2005,2,22,14), Time.local(2005,2,22,3,15,10).in_the_afternoon
+  end
+  
+  def test_change
+    assert_equal Time.local(2006,2,22,15,15,10), Time.local(2005,2,22,15,15,10).change(:year => 2006)
+    assert_equal Time.local(2005,6,22,15,15,10), Time.local(2005,2,22,15,15,10).change(:month => 6)
+    assert_equal Time.local(2012,9,22,15,15,10), Time.local(2005,2,22,15,15,10).change(:year => 2012, :month => 9)
+    assert_equal Time.local(2005,2,22,16), Time.local(2005,2,22,15,15,10).change(:hour => 16)
+    assert_equal Time.local(2005,2,22,16,45), Time.local(2005,2,22,15,15,10).change(:hour => 16, :min => 45)
+    assert_equal Time.local(2005,2,22,15,45), Time.local(2005,2,22,15,15,10).change(:min => 45)
+  end
+end
\ No newline at end of file