diff --git a/DailyStatus.Common/BLL/WorkDaysCalculator.cs b/DailyStatus.Common/BLL/WorkDaysCalculator.cs
index cc4a955..19bee49 100644
--- a/DailyStatus.Common/BLL/WorkDaysCalculator.cs
+++ b/DailyStatus.Common/BLL/WorkDaysCalculator.cs
@@ -8,9 +8,13 @@ namespace DailyStatus.Common.BLL
     public class WorkDaysCalculator
     {
         public TimeSpan MonthExpectedHours(DateTime todayWithHours, TimeSpan workDayStartHour, double numberOfWorkingHoursPerDay, params DateTime[] holidays)
+        {
+            return TimeExpectedHours(new DateTime(todayWithHours.Year, todayWithHours.Month, 1), todayWithHours, workDayStartHour, numberOfWorkingHoursPerDay, holidays);
+        }
+        public TimeSpan TimeExpectedHours(DateTime since, DateTime todayWithHours, TimeSpan workDayStartHour, double numberOfWorkingHoursPerDay, params DateTime[] holidays)
         {
             var today = todayWithHours.Date;
-            var first = new DateTime(today.Year, today.Month, 1);
+            var first = since;
             var workDayStart = today + workDayStartHour;
 
             var worktime = TimeSpan.FromHours(first.BusinessDaysUntil(today, holidays) * numberOfWorkingHoursPerDay);
@@ -32,6 +36,11 @@ public TimeSpan ExpectedWorkedDays(TimeSpan workDayStartHour, double numberOfWor
         {
             return MonthExpectedHours(DateTime.Now, workDayStartHour, numberOfWorkingHoursPerDay, holidaysDuringWeek);
         }
+
+        internal TimeSpan ExpectedWorkedDaysSince(DateTime since, TimeSpan workDayStartHour, double numberOfWorkingHoursPerDay, params DateTime[] holidaysDuringWeek)
+        {
+            return TimeExpectedHours(since, DateTime.Now, workDayStartHour, numberOfWorkingHoursPerDay, holidaysDuringWeek);
+        }
     }
 
 }
diff --git a/DailyStatus.Common/Configuration/DailyStatusConfiguration.cs b/DailyStatus.Common/Configuration/DailyStatusConfiguration.cs
index 236784f..0eaffa8 100644
--- a/DailyStatus.Common/Configuration/DailyStatusConfiguration.cs
+++ b/DailyStatus.Common/Configuration/DailyStatusConfiguration.cs
@@ -22,5 +22,6 @@ public class DailyStatusConfiguration
         public int HoursADay { get; set; }
         public long WorkspaceId { get; set; }
         public List<DateTime> Holidays { get; set; }
+        public DateTime SumSince { get; set; }
     }
 }
diff --git a/DailyStatus.Common/TogglProxy.cs b/DailyStatus.Common/TogglProxy.cs
index 9391672..fe3483c 100644
--- a/DailyStatus.Common/TogglProxy.cs
+++ b/DailyStatus.Common/TogglProxy.cs
@@ -40,6 +40,13 @@ public TimeSpan GetExpectedWorkingTime(WorkDay dayConfig)
                                      dayConfig.NumberOfWorkingHoursPerDay);
         }
 
+        public TimeSpan GetExpectedWorkingTime(WorkDay dayConfig, DateTime since)
+        {
+            return new WorkDaysCalculator()
+                 .ExpectedWorkedDaysSince(since,TimeSpan.FromHours(dayConfig.WorkDayStartHour),
+                                     dayConfig.NumberOfWorkingHoursPerDay);
+        }
+
         public TimeSpan GetDifference(TimeSpan expected, TimeSpan sum)
         {
             var diff = sum - expected;
@@ -67,15 +74,18 @@ public class TogglStatus
         }
 
         public async Task<TogglStatus> GetStatus()
+        {
+            return await GetStatus(new DateTimeOffset(new DateTime(DateTime.Today.Year, DateTime.Today.Month, 1)));
+        }
+
+        public async Task<TogglStatus> GetStatus(DateTimeOffset since)
         {
             try
             {
                 var workspace = await GetWorkspace();
-                var today = DateTime.Today;
-                var offset = new DateTimeOffset(new DateTime(today.Year, today.Month, 1));
-                var entries = await _togglApi.TimeEntries.GetAllSince(offset)
+                var entries = await _togglApi.TimeEntries.GetAllSince(since)
                     .SelectMany(e => e)
-                    .Where(e => !e.ServerDeletedAt.HasValue && e.Start > offset)
+                    .Where(e => !e.ServerDeletedAt.HasValue && e.Start > since)
                     .Where(e => e.WorkspaceId == workspace.Id)
                     .ToList();
                 var sumSeconds = entries.Where(e => e.Duration.HasValue)
diff --git a/DailyStatus.CommonTests/BLL/WorkDaysCalculatorTests.cs b/DailyStatus.CommonTests/BLL/WorkDaysCalculatorTests.cs
index 48cefe4..5ebbf78 100644
--- a/DailyStatus.CommonTests/BLL/WorkDaysCalculatorTests.cs
+++ b/DailyStatus.CommonTests/BLL/WorkDaysCalculatorTests.cs
@@ -73,7 +73,7 @@ public void Given12_11_2019_ShouldReturn6Days_BecauseThereIsOneHolidayOn11_11()
                 todayWithHours: new DateTime(2019, 11, 12),
                 workDayStartHour: TimeSpan.FromHours(10),
                 numberOfWorkingHoursPerDay: 8,
-                new DateTime(2019, 11, 11));
+               new DateTime(2019, 11, 11));
             var expected = TimeSpan.FromHours(6 * 8);
             Assert.AreEqual(expected, actual);
         }
diff --git a/DailyStatus.UI/App.config b/DailyStatus.UI/App.config
index 61841ef..0c9a66a 100644
--- a/DailyStatus.UI/App.config
+++ b/DailyStatus.UI/App.config
@@ -40,6 +40,9 @@
       <setting name="holidays" serializeAs="String">
         <value>1/01/2019,01/06/2019,04/21/2019,04/22/2019,05/01/2019,05/03/2019,06/09/2019,06/20/2019,08/15/2019,11/01/2019,11/11/2019,12/25/2019,12/26/2019</value>
       </setting>
+      <setting name="sum_since" serializeAs="String">
+        <value>2019-09-01</value>
+      </setting>
     </DailyStatus.UI.Properties.Settings>
   </userSettings>
 </configuration>
diff --git a/DailyStatus.UI/DailyStatus.UI.csproj b/DailyStatus.UI/DailyStatus.UI.csproj
index ef7e6d2..34d8741 100644
--- a/DailyStatus.UI/DailyStatus.UI.csproj
+++ b/DailyStatus.UI/DailyStatus.UI.csproj
@@ -117,6 +117,9 @@
       <DependentUpon>App.xaml</DependentUpon>
       <SubType>Code</SubType>
     </Compile>
+    <Compile Include="View\DateTimeSincePrompt.xaml.cs">
+      <DependentUpon>DateTimeSincePrompt.xaml</DependentUpon>
+    </Compile>
     <Compile Include="View\HourRatePrompt.xaml.cs">
       <DependentUpon>HourRatePrompt.xaml</DependentUpon>
     </Compile>
@@ -168,6 +171,10 @@
       <SubType>Designer</SubType>
       <Generator>MSBuild:Compile</Generator>
     </Page>
+    <Page Include="View\DateTimeSincePrompt.xaml">
+      <Generator>MSBuild:Compile</Generator>
+      <SubType>Designer</SubType>
+    </Page>
     <Page Include="View\HourRatePrompt.xaml">
       <Generator>MSBuild:Compile</Generator>
       <SubType>Designer</SubType>
diff --git a/DailyStatus.UI/Properties/Settings.Designer.cs b/DailyStatus.UI/Properties/Settings.Designer.cs
index b5e2c05..0f92f08 100644
--- a/DailyStatus.UI/Properties/Settings.Designer.cs
+++ b/DailyStatus.UI/Properties/Settings.Designer.cs
@@ -95,5 +95,17 @@ public string holidays {
                 this["holidays"] = value;
             }
         }
+        
+        [global::System.Configuration.UserScopedSettingAttribute()]
+        [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]
+        [global::System.Configuration.DefaultSettingValueAttribute("2019-09-01")]
+        public global::System.DateTime sum_since {
+            get {
+                return ((global::System.DateTime)(this["sum_since"]));
+            }
+            set {
+                this["sum_since"] = value;
+            }
+        }
     }
 }
diff --git a/DailyStatus.UI/Properties/Settings.settings b/DailyStatus.UI/Properties/Settings.settings
index 3d5c20b..c33d0f5 100644
--- a/DailyStatus.UI/Properties/Settings.settings
+++ b/DailyStatus.UI/Properties/Settings.settings
@@ -20,5 +20,8 @@
     <Setting Name="holidays" Type="System.String" Scope="User">
       <Value Profile="(Default)">1/01/2019,01/06/2019,04/21/2019,04/22/2019,05/01/2019,05/03/2019,06/09/2019,06/20/2019,08/15/2019,11/01/2019,11/11/2019,12/25/2019,12/26/2019</Value>
     </Setting>
+    <Setting Name="sum_since" Type="System.DateTime" Scope="User">
+      <Value Profile="(Default)">2019-09-01</Value>
+    </Setting>
   </Settings>
 </SettingsFile>
\ No newline at end of file
diff --git a/DailyStatus.UI/SettingsManager.cs b/DailyStatus.UI/SettingsManager.cs
index 9fff6d0..8783485 100644
--- a/DailyStatus.UI/SettingsManager.cs
+++ b/DailyStatus.UI/SettingsManager.cs
@@ -22,6 +22,7 @@ public static DailyStatusConfiguration LoadSettings()
             cfg.HoursADay = stg.hours_a_day;
             cfg.WorkspaceId = stg.api_workspaceid;
             cfg.Holidays = stg.holidays.Split(',').Select(str => DateTime.Parse(str, CultureInfo.InvariantCulture)).ToList();
+            cfg.SumSince = stg.sum_since;
             return cfg;
         }
 
@@ -34,6 +35,7 @@ public static void SaveSettings(DailyStatusConfiguration cfg)
             stg.start_hour = cfg.WorkDayStartHour;
             stg.hours_a_day = cfg.HoursADay;
             stg.holidays = string.Join(",", cfg.Holidays.Select(d => d.ToString(CultureInfo.InvariantCulture)));
+            stg.sum_since = cfg.SumSince;
             stg.Save();
         }
     }
diff --git a/DailyStatus.UI/View/DateTimeSincePrompt.xaml b/DailyStatus.UI/View/DateTimeSincePrompt.xaml
new file mode 100644
index 0000000..09bcc6f
--- /dev/null
+++ b/DailyStatus.UI/View/DateTimeSincePrompt.xaml
@@ -0,0 +1,23 @@
+<Window x:Class="DailyStatus.UI.View.DateTimeSincePrompt"
+        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
+        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
+        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
+        xmlns:local="clr-namespace:DailyStatus.UI.View"
+        mc:Ignorable="d"
+        Title="{Binding WindowTitle}" Height="100" Width="468.22">
+    <Grid>
+        <Grid.ColumnDefinitions>
+            <ColumnDefinition Width="33*"/>
+            <ColumnDefinition Width="59*"/>
+        </Grid.ColumnDefinitions>
+        <Grid.RowDefinitions>
+            <RowDefinition Height="50*"/>
+            <RowDefinition Height="50*"/>
+        </Grid.RowDefinitions>
+        <TextBlock Text="{Binding WindowPrompt}" Grid.RowSpan="1" Grid.ColumnSpan="1"  Grid.Column="0" FontSize="20"/>
+        <DatePicker Name="DatePicker" HorizontalAlignment="Left" Margin="10,0,0,0" Grid.Row="0"  Grid.Column="1" Width="275" />
+        <Button Content="OK" Click="OKButton_Click" Grid.RowSpan="1"  Grid.Row="1" MaxHeight="30" Grid.ColumnSpan="2"/>
+
+    </Grid>
+</Window>
diff --git a/DailyStatus.UI/View/DateTimeSincePrompt.xaml.cs b/DailyStatus.UI/View/DateTimeSincePrompt.xaml.cs
new file mode 100644
index 0000000..93b7182
--- /dev/null
+++ b/DailyStatus.UI/View/DateTimeSincePrompt.xaml.cs
@@ -0,0 +1,71 @@
+using System;
+using System.Collections.Generic;
+using System.ComponentModel;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+using System.Windows;
+using System.Windows.Controls;
+using System.Windows.Data;
+using System.Windows.Documents;
+using System.Windows.Input;
+using System.Windows.Media;
+using System.Windows.Media.Imaging;
+using System.Windows.Shapes;
+
+namespace DailyStatus.UI.View
+{
+    public partial class DateTimeSincePrompt : Window, INotifyPropertyChanged
+    {
+        private string _windowTitle;
+        private string _windowPrompt;
+
+        public DateTimeSincePrompt()
+        {
+            InitializeComponent();
+            DataContext = this;
+        }
+
+        public string WindowTitle
+        {
+            get { return _windowTitle; }
+            set
+            {
+                _windowTitle = value;
+                NotifyPropertyChanged(nameof(WindowTitle));
+            }
+        }
+        public string WindowPrompt
+        {
+            get { return _windowPrompt; }
+            set
+            {
+                _windowPrompt = value;
+                NotifyPropertyChanged(nameof(WindowPrompt));
+            }
+        }
+
+        public DateTime? Date
+        {
+            get
+            {
+                return DatePicker.SelectedDate;
+            }
+            set
+            {
+                DatePicker.SelectedDate = value;
+            }
+        }
+
+        private void OKButton_Click(object sender, RoutedEventArgs e)
+        {
+            DialogResult = true;
+        }
+
+        public event PropertyChangedEventHandler PropertyChanged;
+        void NotifyPropertyChanged(string propertyName)
+        {
+            PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
+        }
+    }
+}
diff --git a/DailyStatus.UI/ViewModel/StatusViewModel.cs b/DailyStatus.UI/ViewModel/StatusViewModel.cs
index 328a95a..363ae13 100644
--- a/DailyStatus.UI/ViewModel/StatusViewModel.cs
+++ b/DailyStatus.UI/ViewModel/StatusViewModel.cs
@@ -253,6 +253,21 @@ public int HoursADay
             }
         }
 
+        public DateTime SumSince
+        {
+            get
+            {
+                return cfg.SumSince;
+            }
+            set
+            {
+                cfg.SumSince = value;
+                NotifyPropertyChanged(nameof(SumSince));
+                NotifyPropertyChanged(nameof(ContextMenu));
+                SaveSettings();
+            }
+        }
+
         public List<MenuItem> ContextMenu
         {
             get
@@ -334,6 +349,23 @@ public List<MenuItem> ContextMenu
                         WorkDayStartHour = (int)newDayStartHour;
                     })
                 });
+                items.Add(new MenuItem()
+                {
+                    Header = "Sum since: " + cfg.SumSince.ToString("dd.MM.yyyy"),
+                    Command = new RelayCommand((_) =>
+                    {
+                        var prompt = new DateTimeSincePrompt
+                        {
+                            Owner = this.Window,
+                            Date = cfg.SumSince,
+                            WindowTitle = "Sum hours since",
+                            WindowPrompt = "Sum since: "
+                        };
+
+                        prompt.ShowDialog();
+                        SumSince = prompt.Date ?? new DateTime(DateTime.Today.Year, DateTime.Today.Month, 1);
+                    })
+                });
                 items.Add(new MenuItem() { Header = "Minimize", Command = new RelayCommand((_) => WindowState = WindowState.Minimized) });
                 items.Add(new MenuItem() { Header = "Close", Command = CloseCommand });
                 return items;
@@ -391,12 +423,13 @@ async Task RefreshData()
                     NotifyPropertyChanged(nameof(ContextMenu));
                 }
                 _togglClient.SetWorkspace(SelectedWorkspace);
-                var actual = (await _togglClient.GetStatus());
+                var since = SumSince;
+                var actual = (await _togglClient.GetStatus(new DateTimeOffset(since)));
                 TodayHours = actual.TodaysHours;
                 IsTimerActive = actual.IsTimerActive;
 
-                var workday = new WorkDay(cfg.HoursADay, cfg.WorkDayStartHour);
-                var expected = _togglClient.GetExpectedWorkingTime(workday);
+                var workday = new WorkDay(HoursADay, WorkDayStartHour);
+                var expected = _togglClient.GetExpectedWorkingTime(workday, since);
                 Diff = _togglClient.GetDifference(expected: expected, sum: actual.TimeInMonth);
                 LastUpdateTime = DateTime.Now;
                 OfflineMode = false;