diff --git a/src/message.rs b/src/message.rs
index 496c35b..77d9d70 100644
--- a/src/message.rs
+++ b/src/message.rs
@@ -1604,6 +1604,7 @@ mod operands {
 
 #[derive(Clone, Debug)]
 enum CalcValue {
+    Calculate(Calculation),
     FType(FieldType),
     Value(Field),
 }
@@ -1613,10 +1614,17 @@ impl CalcValue {
         match self {
             Self::FType(ftype) => ftype.get_default(),
             Self::Value(field) => field.clone(),
+            Self::Calculate(calc) => calc.calculate(),
         }
     }
 }
 
+impl From<Calculation> for CalcValue {
+    fn from(value: Calculation) -> Self {
+        Self::Calculate(value)
+    }
+}
+
 impl From<Field> for CalcValue {
     fn from(value: Field) -> Self {
         Self::Value(value)
@@ -1687,10 +1695,11 @@ mod calcvalues {
         let value = Uuid::new_v4();
         let expected: Field = value.into();
         let result: CalcValue = value.into();
-        match result {
-            CalcValue::FType(_) => unreachable!("got {:?}, should have gotten a field", result),
+        match result.clone() {
             CalcValue::Value(data) => assert_eq!(data, expected),
+            _ => unreachable!("got {:?}, should have gotten a field", result),
         }
+        assert_eq!(result.get(), expected);
     }
 
     #[test]
@@ -1698,10 +1707,11 @@ mod calcvalues {
         let value = "something";
         let expected: Field = value.into();
         let result: CalcValue = value.into();
-        match result {
-            CalcValue::FType(_) => unreachable!("got {:?}, should have gotten a field", result),
+        match result.clone() {
             CalcValue::Value(data) => assert_eq!(data, expected),
+            _ => unreachable!("got {:?}, should have gotten a field", result),
         }
+        assert_eq!(result.get(), expected);
     }
 
     #[test]
@@ -1709,10 +1719,11 @@ mod calcvalues {
         let value = "data".to_string();
         let expected: Field = value.clone().into();
         let result: CalcValue = value.into();
-        match result {
-            CalcValue::FType(_) => unreachable!("got {:?}, should have gotten a field", result),
+        match result.clone() {
             CalcValue::Value(data) => assert_eq!(data, expected),
+            _ => unreachable!("got {:?}, should have gotten a field", result),
         }
+        assert_eq!(result.get(), expected);
     }
 
     #[test]
@@ -1720,10 +1731,11 @@ mod calcvalues {
         let value = true;
         let expected: Field = value.clone().into();
         let result: CalcValue = value.into();
-        match result {
-            CalcValue::FType(_) => unreachable!("got {:?}, should have gotten a field", result),
+        match result.clone() {
             CalcValue::Value(data) => assert_eq!(data, expected),
+            _ => unreachable!("got {:?}, should have gotten a field", result),
         }
+        assert_eq!(result.get(), expected);
     }
 
     #[test]
@@ -1731,10 +1743,11 @@ mod calcvalues {
         let value = Utc::now();
         let expected: Field = value.clone().into();
         let result: CalcValue = value.into();
-        match result {
-            CalcValue::FType(_) => unreachable!("got {:?}, should have gotten a field", result),
+        match result.clone() {
             CalcValue::Value(data) => assert_eq!(data, expected),
+            _ => unreachable!("got {:?}, should have gotten a field", result),
         }
+        assert_eq!(result.get(), expected);
     }
 
     #[test]
@@ -1742,10 +1755,11 @@ mod calcvalues {
         let value = Duration::from_secs(5);
         let expected: Field = value.clone().into();
         let result: CalcValue = value.into();
-        match result {
-            CalcValue::FType(_) => unreachable!("got {:?}, should have gotten a field", result),
+        match result.clone() {
             CalcValue::Value(data) => assert_eq!(data, expected),
+            _ => unreachable!("got {:?}, should have gotten a field", result),
         }
+        assert_eq!(result.get(), expected);
     }
 
     #[test]
@@ -1753,10 +1767,30 @@ mod calcvalues {
         let value: i128 = 5;
         let expected: Field = value.clone().into();
         let result: CalcValue = value.into();
-        match result {
-            CalcValue::FType(_) => unreachable!("got {:?}, should have gotten a field", result),
+        match result.clone() {
             CalcValue::Value(data) => assert_eq!(data, expected),
+            _ => unreachable!("got {:?}, should have gotten a field", result),
         }
+        assert_eq!(result.get(), expected);
+    }
+
+    #[test]
+    fn from_calculation() {
+        let duration = Duration::from_secs(300);
+        let start = Utc::now() + duration;
+        let mut calc = Calculation::new(Operand::Add);
+        calc.add_value(FieldType::DateTime);
+        calc.add_value(duration.clone());
+        let result: CalcValue = calc.into();
+        let data = match result.get() {
+            Field::DateTime(data) => data,
+            _ => unreachable!(),
+        };
+        let stop = Utc::now() + duration;
+        assert!(
+            data > start && data < stop,
+            "should be about 5 minutes ahead"
+        );
     }
 }
 
@@ -3813,6 +3847,35 @@ mod document_files {
             _ => unreachable!("got {:?}: should have gotten reply", action),
         }
     }
+
+    #[test]
+    fn can_calculate_field_values() {
+        let mut doc = TestDocument::new([FieldType::DateTime].to_vec());
+        doc.start();
+        let duration = Duration::from_secs(300);
+        let mut calc = Calculation::new(Operand::Add);
+        calc.add_value(FieldType::DateTime).unwrap();
+        calc.add_value(duration.clone()).unwrap();
+        let mut addition = Addition::new();
+        addition.add_field("field0".to_string(), calc);
+        let start = Utc::now() + duration;
+        doc.send(addition).unwrap();
+        let result = doc.get_receiver().recv_timeout(TIMEOUT).unwrap();
+        let stop = Utc::now() + duration;
+        let action = result.get_action();
+        match action {
+            MsgAction::Reply(data) => {
+                assert_eq!(data.len(), 1);
+                for doc in data.iter() {
+                    match doc.get_field("field0").unwrap() {
+                        Field::DateTime(datetime) => assert!(datetime > start && datetime < stop),
+                        _ => unreachable!("did not get uuid"),
+                    }
+                }
+            }
+            _ => unreachable!("got {:?}: should have gotten reply", action),
+        }
+    }
 }
 
 #[cfg(test)]