diff --git a/application/controllers/Installation.php b/application/controllers/Installation.php
index 31f86de0..b5cbd755 100644
--- a/application/controllers/Installation.php
+++ b/application/controllers/Installation.php
@@ -67,7 +67,7 @@ class Installation extends EA_Controller
             $this->instance->migrate();
 
             // Insert admin
-            $admin['timezone'] = 'UTC';
+            $admin['timezone'] = 'Istanbul (+3:00)'; // REVIEW is it working properly ?!
             $admin['settings']['username'] = $admin['username'];
             $admin['settings']['password'] = $admin['password'];
             $admin['settings']['notifications'] = true;
diff --git a/application/libraries/Timezones.php b/application/libraries/Timezones.php
index 8c833d9c..4d5d5b14 100644
--- a/application/libraries/Timezones.php
+++ b/application/libraries/Timezones.php
@@ -28,15 +28,15 @@ class Timezones
     /**
      * @var string
      */
-    protected string $default = 'UTC';
+    protected string $default = 'Istanbul (+3:00)'; // REVIEW is it working??
 
     /**
      * @var array
      */
     protected array $timezones = [
-        'UTC' => [
-            'UTC' => 'UTC',
-            // 'Türkiye' => 'Istanbul (+3:00)', // TODO add this line in proper way
+        'General' => [
+            'General/UTC' => 'UTC',
+            'General/Istanbul' => 'Istanbul (+3:00)', // REVIEW is this line proper and working correctly???
         ],
         'America' => [
             'America/Adak' => 'Adak (-10:00)',
@@ -531,7 +531,7 @@ class Timezones
      */
     public function get_default_timezone(): string
     {
-        return 'UTC'; // TODO change this to +3 in proper way
+        return 'Istanbul (+3:00)'; // REVIEW  is it working in proper way?         
     }
 
     /**
diff --git a/application/migrations/018_add_timezone_to_users.php b/application/migrations/018_add_timezone_to_users.php
index cd8ad22d..418985df 100644
--- a/application/migrations/018_add_timezone_to_users.php
+++ b/application/migrations/018_add_timezone_to_users.php
@@ -23,7 +23,7 @@ class Migration_Add_timezone_to_users extends EA_Migration
                 'timezone' => [
                     'type' => 'VARCHAR',
                     'constraint' => '256',
-                    'default' => 'UTC',
+                    'default' => 'Istanbul (+3:00)', // REVIEW Works under migration ?
                     'after' => 'notes',
                 ],
             ];
diff --git a/application/views/components/appointments_modal.php b/application/views/components/appointments_modal.php
index 93e55282..6f228af7 100644
--- a/application/views/components/appointments_modal.php
+++ b/application/views/components/appointments_modal.php
@@ -172,7 +172,7 @@
                                             <small>
                                                 <?= lang('current_user') ?>:
                                                 <span>
-                                                    <?= $timezones[session('timezone', 'UTC')] ?>
+                                                    <?= $timezones[session('timezone', 'Istanbul (+3:00)')] ?>
                                                 </span>
                                             </small>
                                         </div>
diff --git a/application/views/components/booking_time_step.php b/application/views/components/booking_time_step.php
index 79732467..7e23ff5d 100644
--- a/application/views/components/booking_time_step.php
+++ b/application/views/components/booking_time_step.php
@@ -23,7 +23,7 @@
                             <?= lang('timezone') ?>
                         </label>
                         <?php component('timezone_dropdown', [
-                            'attributes' => 'id="select-timezone" class="form-control" value="UTC"',
+                            'attributes' => 'id="select-timezone" class="form-control" value="Istanbul (+3:00)"',
                             'grouped_timezones' => $grouped_timezones,
                         ]); ?>
                     </div>
diff --git a/application/views/components/unavailabilities_modal.php b/application/views/components/unavailabilities_modal.php
index 4a2d3a77..d8670ed8 100644
--- a/application/views/components/unavailabilities_modal.php
+++ b/application/views/components/unavailabilities_modal.php
@@ -63,7 +63,7 @@
                                     <small>
                                         <?= lang('current_user') ?>:
                                         <span>
-                                                    <?= $timezones[session('timezone', 'UTC')] ?>
+                                                    <?= $timezones[session('timezone', 'Istanbul (+3:00)')] ?>
                                                 </span>
                                     </small>
                                 </div>