diff --git a/app/Models/RetributionCalculation.php b/app/Models/RetributionCalculation.php
index 3bdd742..6d1e661 100644
--- a/app/Models/RetributionCalculation.php
+++ b/app/Models/RetributionCalculation.php
@@ -56,7 +56,38 @@ class RetributionCalculation extends Model
      */
     public static function generateCalculationId(): string
     {
-        return 'CALC-' . date('Ymd') . '-' . str_pad(mt_rand(1, 9999), 4, '0', STR_PAD_LEFT);
+        $maxAttempts = 10;
+        $attempt = 0;
+        
+        do {
+            // Use microseconds for better uniqueness but keep within 20 char limit
+            // Format: CALC-YYYYMMDD-XXXXX (20 chars exactly)
+            $microseconds = (int) (microtime(true) * 1000) % 100000; // 5 digits max
+            $id = 'CALC-' . date('Ymd') . '-' . str_pad($microseconds, 5, '0', STR_PAD_LEFT);
+            
+            // Check if ID already exists
+            if (!self::where('calculation_id', $id)->exists()) {
+                return $id;
+            }
+            
+            $attempt++;
+            // Add small delay to ensure different microsecond values
+            usleep(1000); // 1ms delay
+            
+        } while ($attempt < $maxAttempts);
+        
+        // Fallback to random 5-digit number if all attempts fail
+        for ($i = 0; $i < 100; $i++) {
+            $random = mt_rand(10000, 99999);
+            $id = 'CALC-' . date('Ymd') . '-' . $random;
+            
+            if (!self::where('calculation_id', $id)->exists()) {
+                return $id;
+            }
+        }
+        
+        // Final fallback - use current timestamp seconds
+        return 'CALC-' . date('Ymd') . '-' . str_pad(time() % 100000, 5, '0', STR_PAD_LEFT);
     }
 
     /**