diff --git a/IRaCIS.Core.Application/Service/Reading/Dto/ReadingCalculateViewModel.cs b/IRaCIS.Core.Application/Service/Reading/Dto/ReadingCalculateViewModel.cs
index e71ab5fc5..ae4150b5a 100644
--- a/IRaCIS.Core.Application/Service/Reading/Dto/ReadingCalculateViewModel.cs
+++ b/IRaCIS.Core.Application/Service/Reading/Dto/ReadingCalculateViewModel.cs
@@ -306,7 +306,13 @@ namespace IRaCIS.Core.Application.Service.Reading.Dto
             get
             {
                 var values = new[] { FirstData, SecondData, ThirdData };
-                var avg = values.Where(x => x.HasValue).Select(x => x.Value).DefaultIfEmpty(0).Average();
+
+                var count = values.Count(x => x.HasValue);
+                if (count == 0)
+                {
+                    return null;
+                }
+                var avg = values.Where(x => x.HasValue).Select(x => x.Value).Average();
                 return avg;
             }
         }