diff --git a/dashboard.py b/dashboard.py
index ebf8d5f..ff153ac 100644
--- a/dashboard.py
+++ b/dashboard.py
@@ -742,7 +742,9 @@ def get_dashboard_data(db_path=DB_PATH):
 
   // Hourly aggregation (filtered by model + range, then bucketed by UTC hour)
   const hourlySrc = (rawData.hourly_by_model || []).filter(r =>
-    selectedModels.has(r.model) && (!cutoff || r.day >= cutoff)
+    selectedModels.has(r.model) &&
+    (!start || r.day >= start) &&
+    (!end || r.day <= end)
   );
   const hourlyAgg = aggregateHourly(hourlySrc, hourlyTZ);
 
diff --git a/tests/test_dashboard.py b/tests/test_dashboard.py
index 76287d1..4da4b4e 100644
--- a/tests/test_dashboard.py
+++ b/tests/test_dashboard.py
@@ -264,5 +264,19 @@ def test_prices_match(self):
             )
 
 
+class TestApplyFilterHourlyRegression(unittest.TestCase):
+    """Regression: applyFilter() referenced `cutoff` (undefined) for the hourly
+    chart filter instead of the `start` bound from getRangeBounds().  Any active
+    date range caused a ReferenceError, silently emptying the hourly chart."""
+
+    def test_no_undefined_cutoff_in_template(self):
+        self.assertNotIn("cutoff", HTML_TEMPLATE)
+
+    def test_hourly_filter_uses_start_bound(self):
+        idx = HTML_TEMPLATE.index("hourlySrc")
+        snippet = HTML_TEMPLATE[idx:idx + 300]
+        self.assertIn("!start || r.day >= start", snippet)
+
+
 if __name__ == "__main__":
     unittest.main()