backend/src/routes/timer.routes.ts

@@ -48,6 +48,16 @@ router.put(
   }
 );
 
+// DELETE /api/timer - Cancel (discard) the ongoing timer without creating a time entry
+router.delete('/', requireAuth, async (req: AuthenticatedRequest, res, next) => {
+  try {
+    await timerService.cancel(req.user!.id);
+    res.status(204).send();
+  } catch (error) {
+    next(error);
+  }
+});
+
 // POST /api/timer/stop - Stop timer
 router.post(
   '/stop',

backend/src/services/timer.service.ts

@@ -138,6 +138,15 @@ export class TimerService {
     });
   }
 
+  async cancel(userId: string) {
+    const timer = await this.getOngoingTimer(userId);
+    if (!timer) {
+      throw new NotFoundError("No timer is running");
+    }
+
+    await prisma.ongoingTimer.delete({ where: { userId } });
+  }
+
   async stop(userId: string, data?: StopTimerInput) {
     const timer = await this.getOngoingTimer(userId);
     if (!timer) {

frontend/src/api/timer.ts

@@ -30,4 +30,8 @@ export const timerApi = {
     });
     return data;
   },
+
+  cancel: async (): Promise<void> => {
+    await apiClient.delete('/timer');
+  },
 };

frontend/src/components/TimerWidget.tsx

@@ -1,5 +1,5 @@
 import { useState, useRef } from "react";
-import { Play, Square, ChevronDown, Pencil, Check, X } from "lucide-react";
+import { Play, Square, ChevronDown, Pencil, Check, X, Trash2 } from "lucide-react";
 import { useTimer } from "@/contexts/TimerContext";
 import { useProjects } from "@/hooks/useProjects";
 import { ProjectColorDot } from "@/components/ProjectColorDot";
@@ -49,12 +49,14 @@ export function TimerWidget() {
     elapsedSeconds,
     startTimer,
     stopTimer,
+    cancelTimer,
     updateTimerProject,
     updateTimerStartTime,
   } = useTimer();
   const { projects } = useProjects();
   const [showProjectSelect, setShowProjectSelect] = useState(false);
   const [error, setError] = useState<string | null>(null);
+  const [confirmCancel, setConfirmCancel] = useState(false);
 
   // Start time editing state
   const [editingStartTime, setEditingStartTime] = useState(false);
@@ -72,6 +74,7 @@ export function TimerWidget() {
 
   const handleStop = async () => {
     setError(null);
+    setConfirmCancel(false);
     try {
       await stopTimer();
     } catch (err) {
@@ -79,6 +82,16 @@ export function TimerWidget() {
     }
   };
 
+  const handleCancelTimer = async () => {
+    setError(null);
+    try {
+      await cancelTimer();
+      setConfirmCancel(false);
+    } catch (err) {
+      setError(err instanceof Error ? err.message : "Failed to cancel timer");
+    }
+  };
+
   const handleProjectChange = async (projectId: string) => {
     setError(null);
     try {
@@ -195,14 +208,44 @@ export function TimerWidget() {
                 )}
               </div>
 
-              {/* Stop Button */}
+              {/* Stop + Cancel Buttons */}
+              <div className="flex items-center space-x-2 shrink-0 sm:order-last">
+                {confirmCancel ? (
+                  <div className="flex items-center space-x-2">
+                    <span className="text-sm text-gray-600">Discard timer?</span>
+                    <button
+                      onClick={() => void handleCancelTimer()}
+                      className="flex items-center space-x-1 px-3 py-2 bg-gray-700 text-white rounded-lg font-medium hover:bg-gray-800 transition-colors text-sm"
+                    >
+                      <Trash2 className="h-4 w-4" />
+                      <span>Discard</span>
+                    </button>
+                    <button
+                      onClick={() => setConfirmCancel(false)}
+                      className="px-3 py-2 text-gray-600 hover:text-gray-800 hover:bg-gray-100 rounded-lg transition-colors text-sm"
+                    >
+                      Keep
+                    </button>
+                  </div>
+                ) : (
+                  <>
+                    <button
+                      onClick={() => setConfirmCancel(true)}
+                      title="Discard timer"
+                      className="p-2 text-gray-400 hover:text-gray-600 hover:bg-gray-100 rounded-lg transition-colors"
+                    >
+                      <Trash2 className="h-5 w-5" />
+                    </button>
                     <button
                       onClick={handleStop}
-                className="flex items-center space-x-2 px-6 py-3 bg-red-600 text-white rounded-lg font-medium hover:bg-red-700 transition-colors shrink-0 sm:order-last"
+                      className="flex items-center space-x-2 px-6 py-3 bg-red-600 text-white rounded-lg font-medium hover:bg-red-700 transition-colors"
                     >
                       <Square className="h-5 w-5 fill-current" />
                       <span>Stop</span>
                     </button>
+                  </>
+                )}
+              </div>
             </div>
 
             {/* Project Selector — full width on mobile, auto on desktop */}

frontend/src/contexts/TimerContext.tsx

@@ -18,6 +18,7 @@ interface TimerContextType {
   startTimer: (projectId?: string) => Promise<void>;
   updateTimerProject: (projectId?: string | null) => Promise<void>;
   updateTimerStartTime: (startTime: string) => Promise<void>;
+  cancelTimer: () => Promise<void>;
   stopTimer: (projectId?: string) => Promise<TimeEntry | null>;
 }
 
@@ -85,6 +86,14 @@ export function TimerProvider({ children }: { children: ReactNode }) {
     },
   });
 
+  // Cancel timer mutation
+  const cancelMutation = useMutation({
+    mutationFn: timerApi.cancel,
+    onSuccess: () => {
+      queryClient.invalidateQueries({ queryKey: ["ongoingTimer"] });
+    },
+  });
+
   // Stop timer mutation
   const stopMutation = useMutation({
     mutationFn: timerApi.stop,
@@ -115,6 +124,10 @@ export function TimerProvider({ children }: { children: ReactNode }) {
     [updateMutation],
   );
 
+  const cancelTimer = useCallback(async () => {
+    await cancelMutation.mutateAsync();
+  }, [cancelMutation]);
+
   const stopTimer = useCallback(
     async (projectId?: string): Promise<TimeEntry | null> => {
       try {
@@ -136,6 +149,7 @@ export function TimerProvider({ children }: { children: ReactNode }) {
         startTimer,
         updateTimerProject,
         updateTimerStartTime,
+        cancelTimer,
         stopTimer,
       }}
     >