diff --git a/apps/backend/internal/analytics/repository/sqlite/repository_test.go b/apps/backend/internal/analytics/repository/sqlite/repository_test.go
index b9afaa6b2f..61d828955f 100644
--- a/apps/backend/internal/analytics/repository/sqlite/repository_test.go
+++ b/apps/backend/internal/analytics/repository/sqlite/repository_test.go
@@ -424,13 +424,19 @@ func TestGetCompletedTaskActivity_ExcludesEphemeralTasks(t *testing.T) {
 	execOrFatal(t, dbConn, `INSERT INTO boards (id, workspace_id, name, created_at, updated_at) VALUES ('board-1', 'ws-1', 'Board', ?, ?)`, nowStr, nowStr)
 	execOrFatal(t, dbConn, `INSERT INTO workflow_steps (id, workflow_id, name, position, created_at, updated_at) VALUES ('step-done', 'board-1', 'Done', 1, ?, ?)`, nowStr, nowStr)
 
-	// Regular completed task
-	execOrFatal(t, dbConn, `INSERT INTO tasks (id, workspace_id, board_id, workflow_step_id, title, is_ephemeral, archived_at, created_at, updated_at) VALUES ('task-regular', 'ws-1', 'board-1', 'step-done', 'Regular', 0, ?, ?, ?)`, nowStr, nowStr, nowStr)
+	// Completed task on last step with session completed_at (NOT archived — isolates session path)
+	execOrFatal(t, dbConn, `INSERT INTO tasks (id, workspace_id, board_id, workflow_step_id, title, is_ephemeral, created_at, updated_at) VALUES ('task-regular', 'ws-1', 'board-1', 'step-done', 'Regular', 0, ?, ?)`, nowStr, nowStr)
+	// Archived task WITHOUT session completed_at — should still count using archived_at
+	execOrFatal(t, dbConn, `INSERT INTO tasks (id, workspace_id, board_id, workflow_step_id, title, is_ephemeral, archived_at, created_at, updated_at) VALUES ('task-archived-no-session', 'ws-1', 'board-1', 'step-done', 'Archived No Session', 0, ?, ?, ?)`, nowStr, nowStr, nowStr)
+	// Task on last step with NO archived_at and NO session completed_at — should NOT count
+	execOrFatal(t, dbConn, `INSERT INTO tasks (id, workspace_id, board_id, workflow_step_id, title, is_ephemeral, created_at, updated_at) VALUES ('task-last-step-no-dates', 'ws-1', 'board-1', 'step-done', 'No Dates', 0, ?, ?)`, nowStr, nowStr)
 	// Ephemeral completed task
 	execOrFatal(t, dbConn, `INSERT INTO tasks (id, workspace_id, board_id, workflow_step_id, title, is_ephemeral, archived_at, created_at, updated_at) VALUES ('task-ephemeral', 'ws-1', 'board-1', '', 'Quick Chat', 1, ?, ?, ?)`, nowStr, nowStr, nowStr)
 
 	execOrFatal(t, dbConn, `INSERT INTO task_sessions (id, task_id, agent_profile_id, state, started_at, completed_at, updated_at) VALUES ('sess-regular', 'task-regular', 'agent-1', 'COMPLETED', ?, ?, ?)`, nowStr, nowStr, nowStr)
 	execOrFatal(t, dbConn, `INSERT INTO task_sessions (id, task_id, agent_profile_id, state, started_at, completed_at, updated_at) VALUES ('sess-ephemeral', 'task-ephemeral', 'agent-1', 'COMPLETED', ?, ?, ?)`, nowStr, nowStr, nowStr)
+	// Session for archived task with NO completed_at
+	execOrFatal(t, dbConn, `INSERT INTO task_sessions (id, task_id, agent_profile_id, state, started_at, updated_at) VALUES ('sess-archived', 'task-archived-no-session', 'agent-1', 'CANCELLED', ?, ?)`, nowStr, nowStr)
 
 	results, err := repo.GetCompletedTaskActivity(ctx, "ws-1", 7)
 	if err != nil {
@@ -441,8 +447,10 @@ func TestGetCompletedTaskActivity_ExcludesEphemeralTasks(t *testing.T) {
 	for _, r := range results {
 		totalCompleted += r.CompletedTasks
 	}
-	if totalCompleted != 1 {
-		t.Errorf("expected 1 completed task (ephemeral excluded), got %d", totalCompleted)
+	// Should count: task-regular (via session completed_at) + task-archived-no-session (via archived_at)
+	// Should NOT count: task-last-step-no-dates (neither date), task-ephemeral (ephemeral)
+	if totalCompleted != 2 {
+		t.Errorf("expected 2 completed tasks (1 via session + 1 via archived_at), got %d", totalCompleted)
 	}
 }
 
diff --git a/apps/backend/internal/analytics/repository/sqlite/stats.go b/apps/backend/internal/analytics/repository/sqlite/stats.go
index 79ba93a3f1..348f5be2e7 100644
--- a/apps/backend/internal/analytics/repository/sqlite/stats.go
+++ b/apps/backend/internal/analytics/repository/sqlite/stats.go
@@ -260,7 +260,7 @@ func (r *Repository) GetCompletedTaskActivity(ctx context.Context, workspaceID s
 	dateStart := dialect.DateNowMinusDays(drv, "?")
 	datePlus := dialect.DatePlusOneDay(drv, "date")
 	curDate := dialect.CurrentDate(drv)
-	dateOfCompleted := dialect.DateOf(drv, "ts.completed_at")
+	dateOfCompleted := dialect.DateOf(drv, "COALESCE(ts.completed_at, t.archived_at)")
 
 	query := fmt.Sprintf(`
 		WITH RECURSIVE dates(date) AS (
@@ -274,13 +274,14 @@ func (r *Repository) GetCompletedTaskActivity(ctx context.Context, workspaceID s
 			SELECT %s as activity_date, COUNT(DISTINCT t.id) as completed_tasks
 			FROM tasks t
 			LEFT JOIN workflow_steps ws ON ws.id = t.workflow_step_id
-			JOIN (
+			LEFT JOIN (
 				SELECT task_id, MAX(completed_at) as completed_at
 				FROM task_sessions WHERE completed_at IS NOT NULL GROUP BY task_id
 			) ts ON ts.task_id = t.id
 			WHERE t.workspace_id = ? AND t.is_ephemeral = 0
 			  AND (t.archived_at IS NOT NULL
 			       OR ws.position = (SELECT MAX(ws2.position) FROM workflow_steps ws2 WHERE ws2.workflow_id = ws.workflow_id))
+			  AND COALESCE(ts.completed_at, t.archived_at) IS NOT NULL
 			GROUP BY %s
 		) activity ON activity.activity_date = d.date
 		ORDER BY d.date ASC