diff --git a/core/class/declarationtva.class.php b/core/class/declarationtva.class.php
index 244e6de..7e75f07 100644
--- a/core/class/declarationtva.class.php
+++ b/core/class/declarationtva.class.php
@@ -354,9 +354,16 @@ class DeclarationTVA
     public function generateDeclarationNumber($period)
     {
         $year = date('Y', strtotime($period['start_date']));
-        $quarter = ceil(date('n', strtotime($period['start_date'])) / 3);
+        $start_month = date('m', strtotime($period['start_date']));
+        $end_month = date('m', strtotime($period['end_date']));
         
-        return 'CA3-' . $year . '-Q' . $quarter . '-' . date('YmdHis');
+        if ($start_month == $end_month) {
+            $month_part = $start_month;
+        } else {
+            $month_part = $start_month . '-' . $end_month;
+        }
+        
+        return 'CA3-' . $year . '-' . $month_part . '-' . date('YmdHis');
     }
 
     /**
@@ -369,9 +376,16 @@ class DeclarationTVA
     public function generateDeclarationNumberFromDates($start_date, $end_date)
     {
         $year = date('Y', strtotime($start_date));
-        $quarter = ceil(date('n', strtotime($start_date)) / 3);
+        $start_month = date('m', strtotime($start_date));
+        $end_month = date('m', strtotime($end_date));
         
-        return 'CA3-' . $year . '-Q' . $quarter . '-' . date('YmdHis');
+        if ($start_month == $end_month) {
+            $month_part = $start_month;
+        } else {
+            $month_part = $start_month . '-' . $end_month;
+        }
+        
+        return 'CA3-' . $year . '-' . $month_part . '-' . date('YmdHis');
     }
 
     /**