diff --git a/src/mouse_tracking/utils/writers.py b/src/mouse_tracking/utils/writers.py
index 5f3102c..e48dd6a 100644
--- a/src/mouse_tracking/utils/writers.py
+++ b/src/mouse_tracking/utils/writers.py
@@ -594,6 +594,8 @@ def write_pose_clip(
         for key, attrs in all_attrs.items():
             for cur_attr, data in attrs.items():
                 out_f[key].attrs.create(cur_attr, data)
+        if len(adjusted_clip_idxs) > 0:
+            out_f["poseest"].attrs.create("clip_start_frame", clip_idxs[0])
 
 
 def downgrade_pose_file(pose_h5_path, disable_id: bool = False):
diff --git a/tests/utils/writers/test_write_pose_clip.py b/tests/utils/writers/test_write_pose_clip.py
index 74868e4..9c8ff28 100644
--- a/tests/utils/writers/test_write_pose_clip.py
+++ b/tests/utils/writers/test_write_pose_clip.py
@@ -865,3 +865,28 @@ def test_comprehensive_pose_file_structure():
         for file_path in [in_pose_file, out_pose_file]:
             if os.path.exists(file_path):
                 os.unlink(file_path)
+
+
+def test_writes_clip_start_frame_attribute():
+    """Test that clip_start_frame attribute is written to the output pose file."""
+    with tempfile.NamedTemporaryFile(suffix=".h5", delete=False) as tmp_in:
+        in_pose_file = tmp_in.name
+    with tempfile.NamedTemporaryFile(suffix=".h5", delete=False) as tmp_out:
+        out_pose_file = tmp_out.name
+
+    try:
+        with h5py.File(in_pose_file, "w") as f:
+            poseest = f.create_group("poseest")
+            poseest.create_dataset(
+                "points", data=np.random.rand(20, 1, 12, 2).astype(np.float32)
+            )
+            poseest.attrs["version"] = [3, 0]
+
+        write_pose_clip(in_pose_file, out_pose_file, range(5, 15))
+
+        with h5py.File(out_pose_file, "r") as f:
+            assert f["poseest"].attrs["clip_start_frame"] == 5
+    finally:
+        for path in [in_pose_file, out_pose_file]:
+            if os.path.exists(path):
+                os.unlink(path)