diff --git a/Userland/Applications/Calendar/AddEventDialog.cpp b/Userland/Applications/Calendar/AddEventDialog.cpp
index ab688e9075..0609815cc8 100644
--- a/Userland/Applications/Calendar/AddEventDialog.cpp
+++ b/Userland/Applications/Calendar/AddEventDialog.cpp
@@ -60,6 +60,7 @@ AddEventDialog::AddEventDialog(Core::DateTime date_time, EventManager& event_man
                 m_end_date_time.set_date(new_date.value());
                 update_end_date();
             }
+            update_duration();
 
             m_start_date_box->set_text(MUST(m_start_date_time.to_string(DATE_FORMAT)));
         }
@@ -79,6 +80,7 @@ AddEventDialog::AddEventDialog(Core::DateTime date_time, EventManager& event_man
                 m_start_date_time.set_date(new_date.value());
                 update_start_date();
             }
+            update_duration();
 
             m_end_date_box->set_text(MUST(m_end_date_time.to_string(DATE_FORMAT)));
         }
@@ -87,6 +89,9 @@ AddEventDialog::AddEventDialog(Core::DateTime date_time, EventManager& event_man
     m_end_hour_box = *widget->find_descendant_of_type_named<GUI::SpinBox>("end_hour");
     m_end_minute_box = *widget->find_descendant_of_type_named<GUI::SpinBox>("end_minute");
 
+    m_duration_hour_box = *widget->find_descendant_of_type_named<GUI::SpinBox>("duration_hour");
+    m_duration_minute_box = *widget->find_descendant_of_type_named<GUI::SpinBox>("duration_minute");
+
     auto& ok_button = *widget->find_descendant_of_type_named<GUI::Button>("ok_button");
     ok_button.on_click = [&](auto) {
         auto successful = add_event_to_calendar().release_value_but_fixme_should_propagate_errors();
@@ -106,6 +111,7 @@ AddEventDialog::AddEventDialog(Core::DateTime date_time, EventManager& event_man
             m_end_date_time.set_time_only(hour, minute);
             update_end_date();
         }
+        update_duration();
     };
     auto update_ending_input_values = [&, this]() {
         auto hour = m_end_hour_box->value();
@@ -115,15 +121,25 @@ AddEventDialog::AddEventDialog(Core::DateTime date_time, EventManager& event_man
             m_start_date_time.set_time_only(hour, minute);
             update_start_date();
         }
+        update_duration();
+    };
+    auto update_duration_input_values = [&, this]() {
+        auto hour = m_duration_hour_box->value();
+        auto minute = m_duration_minute_box->value();
+        m_end_date_time = Core::DateTime::from_timestamp(m_start_date_time.timestamp() + (hour * 60 + minute) * 60);
+        update_end_date();
     };
 
     m_start_hour_box->on_change = [update_starting_input_values](auto) { update_starting_input_values(); };
     m_start_minute_box->on_change = [update_starting_input_values](auto) { update_starting_input_values(); };
     m_end_hour_box->on_change = [update_ending_input_values](auto) { update_ending_input_values(); };
     m_end_minute_box->on_change = [update_ending_input_values](auto) { update_ending_input_values(); };
+    m_duration_hour_box->on_change = [update_duration_input_values](auto) { update_duration_input_values(); };
+    m_duration_minute_box->on_change = [update_duration_input_values](auto) { update_duration_input_values(); };
 
     update_start_date();
     update_end_date();
+    update_duration();
 }
 
 ErrorOr<bool> AddEventDialog::add_event_to_calendar()
@@ -157,4 +173,14 @@ void AddEventDialog::update_end_date()
     m_end_minute_box->set_value(m_end_date_time.minute(), GUI::AllowCallback::No);
 }
 
+void AddEventDialog::update_duration()
+{
+    auto difference_in_seconds = m_end_date_time.timestamp() - m_start_date_time.timestamp();
+    auto hours = difference_in_seconds / (60 * 60);
+    auto minutes = (difference_in_seconds - hours * (60 * 60)) / 60;
+
+    m_duration_hour_box->set_value(hours, GUI::AllowCallback::No);
+    m_duration_minute_box->set_value(minutes, GUI::AllowCallback::No);
+}
+
 }
diff --git a/Userland/Applications/Calendar/AddEventDialog.gml b/Userland/Applications/Calendar/AddEventDialog.gml
index 8a0c43e72c..13670d9cac 100644
--- a/Userland/Applications/Calendar/AddEventDialog.gml
+++ b/Userland/Applications/Calendar/AddEventDialog.gml
@@ -102,6 +102,35 @@
         }
     }
 
+    @GUI::Widget {
+        fill_with_background_color: true
+        fixed_height: 25
+        layout: @GUI::HorizontalBoxLayout {
+            spacing: 4
+        }
+
+        @GUI::Label {
+            text: "Duration:"
+            text_alignment: "CenterLeft"
+            fixed_height: 14
+            font_weight: "Bold"
+        }
+
+        @GUI::SpinBox {
+            name: "duration_hour"
+            fixed_size: [50, 20]
+            min: 0
+            max: 999999
+        }
+
+        @GUI::SpinBox {
+            name: "duration_minute"
+            fixed_size: [40, 20]
+            min: 0
+            max: 59
+        }
+    }
+
     @GUI::Layout::Spacer {}
 
     @GUI::Widget {
diff --git a/Userland/Applications/Calendar/AddEventDialog.h b/Userland/Applications/Calendar/AddEventDialog.h
index c42b28275b..2989471e1e 100644
--- a/Userland/Applications/Calendar/AddEventDialog.h
+++ b/Userland/Applications/Calendar/AddEventDialog.h
@@ -34,6 +34,7 @@ private:
 
     void update_start_date();
     void update_end_date();
+    void update_duration();
 
     Core::DateTime m_start_date_time;
     Core::DateTime m_end_date_time;
@@ -45,6 +46,8 @@ private:
     RefPtr<GUI::SpinBox> m_start_minute_box;
     RefPtr<GUI::SpinBox> m_end_hour_box;
     RefPtr<GUI::SpinBox> m_end_minute_box;
+    RefPtr<GUI::SpinBox> m_duration_hour_box;
+    RefPtr<GUI::SpinBox> m_duration_minute_box;
 };
 
 }