diff --git a/event.go b/event.go
index aa4c48a..1175f2e 100644
--- a/event.go
+++ b/event.go
@@ -278,7 +278,7 @@ func (e *Event) Time(key string, t time.Time) *Event {
 	return e
 }
 
-// Dur adds the fields key with duration d stored as zerolog.DurationFieldUnit.
+// Dur adds the field key with duration d stored as zerolog.DurationFieldUnit.
 // If zerolog.DurationFieldInteger is true, durations are rendered as integer
 // instead of float.
 func (e *Event) Dur(key string, d time.Duration) *Event {
@@ -289,6 +289,21 @@ func (e *Event) Dur(key string, d time.Duration) *Event {
 	return e
 }
 
+// TimeDiff adds the field key with positive duration between time t and start.
+// If time t is not greater than start, duration will be 0.
+// Duration format follows the same principle as Dur().
+func (e *Event) TimeDiff(key string, t time.Time, start time.Time) *Event {
+	if !e.enabled {
+		return e
+	}
+	var d time.Duration
+	if t.After(start) {
+		d = t.Sub(start)
+	}
+	e.buf = appendDuration(e.buf, key, d)
+	return e
+}
+
 // Interface adds the field key with i marshaled using reflection.
 func (e *Event) Interface(key string, i interface{}) *Event {
 	if !e.enabled {
diff --git a/log_test.go b/log_test.go
index 49a233d..17903d5 100644
--- a/log_test.go
+++ b/log_test.go
@@ -119,9 +119,11 @@ func TestFields(t *testing.T) {
 		Uint64("uint64", 10).
 		Float32("float32", 11).
 		Float64("float64", 12).
+		Dur("dur", 1*time.Second).
 		Time("time", time.Time{}).
+		TimeDiff("diff", time.Now(), time.Now().Add(-10*time.Second)).
 		Msg("")
-	if got, want := out.String(), `{"foo":"bar","error":"some error","bool":true,"int":1,"int8":2,"int16":3,"int32":4,"int64":5,"uint":6,"uint8":7,"uint16":8,"uint32":9,"uint64":10,"float32":11,"float64":12,"time":"0001-01-01T00:00:00Z"}`+"\n"; got != want {
+	if got, want := out.String(), `{"foo":"bar","error":"some error","bool":true,"int":1,"int8":2,"int16":3,"int32":4,"int64":5,"uint":6,"uint8":7,"uint16":8,"uint32":9,"uint64":10,"float32":11,"float64":12,"dur":1000,"time":"0001-01-01T00:00:00Z","diff":10000}`+"\n"; got != want {
 		t.Errorf("invalid log output: got %q, want %q", got, want)
 	}
 }
@@ -146,7 +148,9 @@ func TestFieldsDisabled(t *testing.T) {
 		Uint64("uint64", 10).
 		Float32("float32", 11).
 		Float64("float64", 12).
+		Dur("dur", 1*time.Second).
 		Time("time", time.Time{}).
+		TimeDiff("diff", time.Now(), time.Now().Add(-10*time.Second)).
 		Msg("")
 	if got, want := out.String(), ""; got != want {
 		t.Errorf("invalid log output: got %q, want %q", got, want)