diff --git a/scroll-animations/scroll-timelines/duration.html b/scroll-animations/scroll-timelines/duration.html
new file mode 100644
index 00000000000000..245670de2aedf8
--- /dev/null
+++ b/scroll-animations/scroll-timelines/duration.html
@@ -0,0 +1,16 @@
+<!DOCTYPE html>
+<meta charset="utf-8">
+<title>ScrollTimeline.duration</title>
+<link rel="help" href="https://drafts.csswg.org/web-animations-2/#dom-animationtimeline-duration">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+
+<script>
+'use strict';
+
+test(t => {
+  const timeline = new ScrollTimeline();
+  assert_equals(timeline.duration.toString(), '100%');
+}, 'The duration of a scroll timeline is 100%');
+
+</script>
diff --git a/scroll-animations/view-timelines/duration.html b/scroll-animations/view-timelines/duration.html
new file mode 100644
index 00000000000000..05d35801307d5c
--- /dev/null
+++ b/scroll-animations/view-timelines/duration.html
@@ -0,0 +1,16 @@
+<!DOCTYPE html>
+<meta charset="utf-8">
+<title>ViewTimeline.duration</title>
+<link rel="help" href="https://drafts.csswg.org/web-animations-2/#dom-animationtimeline-duration">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+
+<script>
+'use strict';
+
+test(t => {
+  const timeline = new ViewTimeline();
+  assert_equals(timeline.duration.toString(), '100%');
+}, 'The duration of a view timeline is 100%');
+
+</script>
diff --git a/web-animations/interfaces/DocumentTimeline/duration.tentative.html b/web-animations/interfaces/DocumentTimeline/duration.tentative.html
new file mode 100644
index 00000000000000..8a307f986e9757
--- /dev/null
+++ b/web-animations/interfaces/DocumentTimeline/duration.tentative.html
@@ -0,0 +1,20 @@
+<!DOCTYPE html>
+<meta charset=utf-8>
+<title>DocumentTimeline.duration</title>
+<link rel="help" href="https://drafts.csswg.org/web-animations-2/#dom-animationtimeline-duration">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="../../testcommon.js"></script>
+<script src="../../resources/timing-override.js"></script>
+<body>
+<div id="log"></div>
+<script>
+'use strict';
+
+test(t => {
+  const timeline = new DocumentTimeline();
+  assert_equals(timeline.duration, null);
+}, 'A document timeline does not have a duration');
+
+</script>
+</body>
