diff --git a/core/src/main/kotlin/net/corda/core/contracts/TimeWindow.kt b/core/src/main/kotlin/net/corda/core/contracts/TimeWindow.kt
index c8c650257d..8126292138 100644
--- a/core/src/main/kotlin/net/corda/core/contracts/TimeWindow.kt
+++ b/core/src/main/kotlin/net/corda/core/contracts/TimeWindow.kt
@@ -64,6 +64,17 @@ abstract class TimeWindow {
      */
     abstract val midpoint: Instant?
 
+    /**
+     * Returns the duration between [fromTime] and [untilTime] if both are non-null. Otherwise returns null.
+     */
+    val length: Duration? get() {
+        return if (fromTime == null || untilTime == null) {
+            null
+        } else {
+            Duration.between(fromTime, untilTime)
+        }
+    }
+
     /** Returns true iff the given [instant] is within the time interval of this [TimeWindow]. */
     abstract operator fun contains(instant: Instant): Boolean
 
diff --git a/core/src/test/kotlin/net/corda/core/contracts/TimeWindowTest.kt b/core/src/test/kotlin/net/corda/core/contracts/TimeWindowTest.kt
index 453b01eb65..f0da2499b9 100644
--- a/core/src/test/kotlin/net/corda/core/contracts/TimeWindowTest.kt
+++ b/core/src/test/kotlin/net/corda/core/contracts/TimeWindowTest.kt
@@ -1,9 +1,12 @@
 package net.corda.core.contracts
 
+import net.corda.core.internal.div
+import net.corda.core.internal.times
 import net.corda.core.utilities.millis
 import net.corda.core.utilities.minutes
 import org.assertj.core.api.Assertions.assertThat
 import org.junit.Test
+import java.time.Duration
 import java.time.Instant
 import java.time.LocalDate
 import java.time.ZoneOffset.UTC
@@ -17,6 +20,7 @@ class TimeWindowTest {
         assertThat(timeWindow.fromTime).isEqualTo(now)
         assertThat(timeWindow.untilTime).isNull()
         assertThat(timeWindow.midpoint).isNull()
+        assertThat(timeWindow.length).isNull()
         assertThat(timeWindow.contains(now - 1.millis)).isFalse()
         assertThat(timeWindow.contains(now)).isTrue()
         assertThat(timeWindow.contains(now + 1.millis)).isTrue()
@@ -28,6 +32,7 @@ class TimeWindowTest {
         assertThat(timeWindow.fromTime).isNull()
         assertThat(timeWindow.untilTime).isEqualTo(now)
         assertThat(timeWindow.midpoint).isNull()
+        assertThat(timeWindow.length).isNull()
         assertThat(timeWindow.contains(now - 1.millis)).isTrue()
         assertThat(timeWindow.contains(now)).isFalse()
         assertThat(timeWindow.contains(now + 1.millis)).isFalse()
@@ -42,6 +47,7 @@ class TimeWindowTest {
         assertThat(timeWindow.fromTime).isEqualTo(fromTime)
         assertThat(timeWindow.untilTime).isEqualTo(untilTime)
         assertThat(timeWindow.midpoint).isEqualTo(today.atTime(12, 15).toInstant(UTC))
+        assertThat(timeWindow.length).isEqualTo(Duration.between(fromTime, untilTime))
         assertThat(timeWindow.contains(fromTime - 1.millis)).isFalse()
         assertThat(timeWindow.contains(fromTime)).isTrue()
         assertThat(timeWindow.contains(fromTime + 1.millis)).isTrue()
@@ -51,17 +57,21 @@ class TimeWindowTest {
 
     @Test
     fun fromStartAndDuration() {
-        val timeWindow = TimeWindow.fromStartAndDuration(now, 10.minutes)
+        val duration = 10.minutes
+        val timeWindow = TimeWindow.fromStartAndDuration(now, duration)
         assertThat(timeWindow.fromTime).isEqualTo(now)
-        assertThat(timeWindow.untilTime).isEqualTo(now + 10.minutes)
-        assertThat(timeWindow.midpoint).isEqualTo(now + 5.minutes)
+        assertThat(timeWindow.untilTime).isEqualTo(now + duration)
+        assertThat(timeWindow.midpoint).isEqualTo(now + duration / 2)
+        assertThat(timeWindow.length).isEqualTo(duration)
     }
 
     @Test
     fun withTolerance() {
-        val timeWindow = TimeWindow.withTolerance(now, 10.minutes)
-        assertThat(timeWindow.fromTime).isEqualTo(now - 10.minutes)
-        assertThat(timeWindow.untilTime).isEqualTo(now + 10.minutes)
+        val tolerance = 10.minutes
+        val timeWindow = TimeWindow.withTolerance(now, tolerance)
+        assertThat(timeWindow.fromTime).isEqualTo(now - tolerance)
+        assertThat(timeWindow.untilTime).isEqualTo(now + tolerance)
         assertThat(timeWindow.midpoint).isEqualTo(now)
+        assertThat(timeWindow.length).isEqualTo(tolerance * 2)
     }
 }
diff --git a/docs/source/changelog.rst b/docs/source/changelog.rst
index 0931e57561..ddc74beb2a 100644
--- a/docs/source/changelog.rst
+++ b/docs/source/changelog.rst
@@ -46,6 +46,9 @@ UNRELEASED
   allows services to start flows marked with the ``StartableByService`` annotation. For backwards compatability
   service classes with only ``ServiceHub`` constructors will still work.
 
+* ``TimeWindow`` now has a ``length`` property that returns the length of the time-window, or ``null`` if the
+  time-window is open-ended.
+
 .. _changelog_v1:
 
 Release 1.0