diff --git a/apps/activity/templates/activity/activity_form.html b/apps/activity/templates/activity/activity_form.html
index c472d3cb..757b47b0 100644
--- a/apps/activity/templates/activity/activity_form.html
+++ b/apps/activity/templates/activity/activity_form.html
@@ -17,4 +17,24 @@ SPDX-License-Identifier: GPL-3.0-or-later
     </form>
   </div>
 </div>
-{% endblock %}
\ No newline at end of file
+<script>
+  var date_end = document.getElementById("id_date_end");
+  var date_start = document.getElementById("id_date_start");
+  
+  function update_date_end (){
+    if(date_end.value=="" || date_end.value<date_start.value){
+      date_end.value = date_start.value;
+    };
+  };
+  
+  function update_date_start (){
+    if(date_start.value=="" || date_end.value<date_start.value){
+      date_start.value = date_end.value;
+    };
+  };
+  
+  date_start.addEventListener('focusout', update_date_end);
+  date_end.addEventListener('focusout', update_date_start);
+  
+</script>
+{% endblock %}