diff --git a/lib/models/timer.dart b/lib/models/timer.dart
index c9dc055..0092590 100644
--- a/lib/models/timer.dart
+++ b/lib/models/timer.dart
@@ -1,33 +1,45 @@
 import 'package:meta/meta.dart';
 import 'package:time_progress_calculator/persistence/timer_entity.dart';
+import 'package:time_progress_calculator/uuid.dart';
 
 @immutable
 class Timer {
+  final String id;
   final DateTime startTime;
   final DateTime endTime;
 
-  Timer(this.startTime, this.endTime);
+  Timer(this.startTime, this.endTime, {String id})
+      : id = id ?? Uuid().generateV4();
 
-  Timer copyWith({DateTime startTime, DateTime endTime}) {
-    return Timer(startTime ?? this.startTime, endTime ?? this.endTime);
+  Timer copyWith({String id, DateTime startTime, DateTime endTime}) {
+    return Timer(
+      startTime ?? this.startTime,
+      endTime ?? this.endTime,
+      id: id ?? this.id,
+    );
   }
 
   @override
-  int get hashCode => startTime.hashCode ^ endTime.hashCode;
+  int get hashCode => id.hashCode ^ startTime.hashCode ^ endTime.hashCode;
 
   @override
   bool operator ==(Object other) =>
       identical(this, other) ||
       other is Timer &&
           runtimeType == other.runtimeType &&
+          id == other.id &&
           startTime == other.startTime &&
           endTime == other.endTime;
 
   TimerEntity toEntity() {
-    return TimerEntity(startTime, endTime);
+    return TimerEntity(id, startTime, endTime);
   }
 
   static Timer fromEntity(TimerEntity entity) {
-    return Timer(entity.startTime, entity.endTime);
+    return Timer(
+      entity.startTime,
+      entity.endTime,
+      id: entity.id ?? Uuid().generateV4(),
+    );
   }
 }
diff --git a/lib/persistence/timer_entity.dart b/lib/persistence/timer_entity.dart
index 08e384f..81d0ca5 100644
--- a/lib/persistence/timer_entity.dart
+++ b/lib/persistence/timer_entity.dart
@@ -1,32 +1,36 @@
 class TimerEntity {
+  final String id;
   final DateTime startTime;
   final DateTime endTime;
 
-  TimerEntity(this.startTime, this.endTime);
+  TimerEntity(this.id, this.startTime, this.endTime);
 
   @override
-  int get hashCode => startTime.hashCode ^ endTime.hashCode;
+  int get hashCode => id.hashCode ^ startTime.hashCode ^ endTime.hashCode;
 
   @override
   bool operator ==(Object other) =>
       identical(this, other) ||
       other is TimerEntity &&
           runtimeType == other.runtimeType &&
+          id == other.id &&
           startTime == other.startTime &&
           endTime == other.endTime;
 
   Map<String, Object> toJson() {
     return {
+      "id": id,
       "startTime": startTime.millisecondsSinceEpoch,
       "endTime": startTime.millisecondsSinceEpoch
     };
   }
 
   static TimerEntity fromJson(Map<String, Object> json) {
-    DateTime startTime =
+    final String id = json["id"] as String;
+    final DateTime startTime =
         DateTime.fromMillisecondsSinceEpoch(json["startTime"] as int);
-    DateTime endTime =
+    final DateTime endTime =
         DateTime.fromMillisecondsSinceEpoch(json["endTime"] as int);
-    return TimerEntity(startTime, endTime);
+    return TimerEntity(id, startTime, endTime);
   }
 }