diff --git a/agenda/stats.py b/agenda/stats.py
new file mode 100644
index 0000000..930e948
--- /dev/null
+++ b/agenda/stats.py
@@ -0,0 +1,45 @@
+"""Trip statistic functions."""
+
+from collections import defaultdict
+
+from agenda.types import StrDict, Trip
+
+
+def calculate_yearly_stats(trips: list[Trip]) -> dict[int, StrDict]:
+    """Calculate total distance and distance by transport type grouped by year."""
+    yearly_stats: defaultdict[int, StrDict] = defaultdict(dict)
+    for trip in trips:
+        year = trip.start.year
+        dist = trip.total_distance()
+        yearly_stats[year].setdefault("count", 0)
+        yearly_stats[year]["count"] += 1
+
+        for c in trip.conferences:
+            yearly_stats[c["start"].year].setdefault("conferences", 0)
+            yearly_stats[c["start"].year]["conferences"] += 1
+
+        if dist:
+            yearly_stats[year]["total_distance"] = (
+                yearly_stats[year].get("total_distance", 0) + trip.total_distance()
+            )
+
+        for transport_type, distance in trip.distances_by_transport_type():
+            yearly_stats[year].setdefault("distances_by_transport_type", {})
+            yearly_stats[year]["distances_by_transport_type"][transport_type] = (
+                yearly_stats[year]["distances_by_transport_type"].get(transport_type, 0)
+                + distance
+            )
+
+        for country in trip.countries:
+            if country.alpha_2 == "GB":
+                continue
+            yearly_stats[year].setdefault("countries", set())
+            yearly_stats[year]["countries"].add(country)
+        for leg in trip.travel:
+            if leg["type"] == "flight":
+                yearly_stats[year].setdefault("flight_count", 0)
+                yearly_stats[year]["flight_count"] += 1
+            if leg["type"] == "train":
+                yearly_stats[year].setdefault("train_count", 0)
+                yearly_stats[year]["train_count"] += 1
+    return dict(yearly_stats)
diff --git a/agenda/trip.py b/agenda/trip.py
index ca0e283..3d41f2d 100644
--- a/agenda/trip.py
+++ b/agenda/trip.py
@@ -3,7 +3,6 @@
 import decimal
 import os
 import typing
-from collections import defaultdict
 from datetime import date, datetime, time
 from zoneinfo import ZoneInfo
 
@@ -88,6 +87,11 @@ def load_ferries(
 
 
 def depart_datetime(item: StrDict) -> datetime:
+    """Return a datetime for this travel item.
+
+    If the travel item already has a datetime return that, otherwise if the
+    departure time is just a date return midnight UTC for that date.
+    """
     depart = item["depart"]
     if isinstance(depart, datetime):
         return depart
@@ -389,43 +393,3 @@ def get_coordinates_and_routes(
             route["geojson"] = read_geojson(data_dir, route.pop("geojson_filename"))
 
     return (coordinates, routes)
-
-
-def calculate_yearly_stats(trips: list[Trip]) -> dict[int, StrDict]:
-    """Calculate total distance and distance by transport type grouped by year."""
-    yearly_stats: defaultdict[int, StrDict] = defaultdict(dict)
-    for trip in trips:
-        year = trip.start.year
-        dist = trip.total_distance()
-        yearly_stats[year].setdefault("count", 0)
-        yearly_stats[year]["count"] += 1
-
-        for c in trip.conferences:
-            yearly_stats[c["start"].year].setdefault("conferences", 0)
-            yearly_stats[c["start"].year]["conferences"] += 1
-
-        if dist:
-            yearly_stats[year]["total_distance"] = (
-                yearly_stats[year].get("total_distance", 0) + trip.total_distance()
-            )
-
-        for transport_type, distance in trip.distances_by_transport_type():
-            yearly_stats[year].setdefault("distances_by_transport_type", {})
-            yearly_stats[year]["distances_by_transport_type"][transport_type] = (
-                yearly_stats[year]["distances_by_transport_type"].get(transport_type, 0)
-                + distance
-            )
-
-        for country in trip.countries:
-            if country.alpha_2 == "GB":
-                continue
-            yearly_stats[year].setdefault("countries", set())
-            yearly_stats[year]["countries"].add(country)
-        for leg in trip.travel:
-            if leg["type"] == "flight":
-                yearly_stats[year].setdefault("flight_count", 0)
-                yearly_stats[year]["flight_count"] += 1
-            if leg["type"] == "train":
-                yearly_stats[year].setdefault("train_count", 0)
-                yearly_stats[year]["train_count"] += 1
-    return dict(yearly_stats)