diff --git a/docs/architecture.adoc b/docs/architecture.adoc
index 40e25e2..408c206 100644
--- a/docs/architecture.adoc
+++ b/docs/architecture.adoc
@@ -233,6 +233,23 @@ assembling any HTML; the URL pattern excludes quote characters, so a
 matched URL can never break out of the `href="..."` attribute. Every
 other value is HTML-escaped before being handed to `Popup#setHTML`.
 
+Track properties:: Every track feature (both formats) also carries
+`distance_meters`, `elevation_gain_meters`, `duration_secs` and
+`point_count`, computed once server-side by `Maptool::TrackStats`
+(`lib/maptool/track_stats.rb`, shared by `Gpx`/`Fit` so neither
+duplicates the haversine formula) rather than in the browser — cheap
+either way, but it means a GPX and a FIT file end up with the same
+properties shape, so the frontend doesn't need to know which format it
+got. Distance sums the haversine distance between consecutive points;
+elevation gain sums only the positive deltas (descents don't
+subtract); duration is the gap between the first and last known
+timestamp, skipping unknown ones in between — `nil` for any of these
+where the source data doesn't have enough to compute it (e.g. a GPX
+file with no `<time>` elements has `duration_secs: nil`). Hovering a
+track line (rather than clicking, unlike a waypoint — these properties
+describe the whole line, not whichever point the cursor happens to be
+over) shows them in the same popup mechanism.
+
 == Live GNSS position
 
 A "GNSS" map control (`public/js/gnss.js`) shows the fix from a local
diff --git a/lib/maptool/fit.rb b/lib/maptool/fit.rb
index d558b0e..6a65ea3 100644
--- a/lib/maptool/fit.rb
+++ b/lib/maptool/fit.rb
@@ -1,3 +1,5 @@
+require_relative "track_stats"
+
 module Maptool
   # Converts a Garmin FIT file (binary — see https://developer.garmin.com/fit/)
   # to a GeoJSON FeatureCollection, in the same shape Gpx.to_geojson produces
@@ -14,6 +16,7 @@ module Maptool
     FIELD_POSITION_LAT = 0
     FIELD_POSITION_LONG = 1
     FIELD_ALTITUDE = 2
+    FIELD_TIMESTAMP = 253
     FIELD_ENHANCED_ALTITUDE = 78
     SEMICIRCLE_TO_DEGREES = 180.0 / (2**31)
 
@@ -26,16 +29,16 @@ module Maptool
     end
 
     def self.to_geojson(path)
-      points = parse(File.binread(path))
-      features = points.empty? ? [] : [track_feature(points)]
+      records = parse(File.binread(path))
+      features = records.empty? ? [] : [track_feature(records.map(&:first), records.map(&:last))]
       { "type" => "FeatureCollection", "features" => features }
     end
 
-    def self.track_feature(points)
+    def self.track_feature(coordinates, times)
       {
         "type" => "Feature",
-        "geometry" => { "type" => "MultiLineString", "coordinates" => [points] },
-        "properties" => { "kind" => "track", "name" => nil },
+        "geometry" => { "type" => "MultiLineString", "coordinates" => [coordinates] },
+        "properties" => { "kind" => "track", "name" => nil }.merge(TrackStats.compute(coordinates, times: times)),
       }
     end
     private_class_method :track_feature
@@ -50,7 +53,7 @@ module Maptool
 
       offset = header_size
       definitions = {}
-      points = []
+      records = []
 
       while offset < data_end
         header = data.getbyte(offset)
@@ -59,7 +62,7 @@ module Maptool
         if header & 0x80 != 0
           local_type = (header >> 5) & 0x3
           definition = definitions[local_type] or raise ParseError, "data message before its definition"
-          offset = read_data_message(data, offset, definition, points)
+          offset = read_data_message(data, offset, definition, records)
         elsif header & 0x40 != 0
           local_type = header & 0x0F
           definition, offset = read_definition(data, offset, header & 0x20 != 0)
@@ -67,11 +70,11 @@ module Maptool
         else
           local_type = header & 0x0F
           definition = definitions[local_type] or raise ParseError, "data message before its definition"
-          offset = read_data_message(data, offset, definition, points)
+          offset = read_data_message(data, offset, definition, records)
         end
       end
 
-      points
+      records
     rescue ArgumentError, NoMethodError => e
       raise ParseError, e.message
     end
@@ -104,20 +107,20 @@ module Maptool
     end
     private_class_method :read_definition
 
-    def self.read_data_message(data, offset, definition, points)
+    def self.read_data_message(data, offset, definition, records)
       if definition.global_mesg_num == RECORD_MESSAGE_NUM
-        point = extract_point(data, offset, definition)
-        points << point if point
+        record = extract_record(data, offset, definition)
+        records << record if record
       end
       offset + definition.total_size
     end
     private_class_method :read_data_message
 
-    # Only reads the 3 fields the map needs; every other field in the
-    # message (heart rate, cadence, power, ...) is walked past via its
-    # declared size without being interpreted.
-    def self.extract_point(data, offset, definition)
-      lat = lon = altitude = nil
+    # Only reads the 4 fields the map/its properties need; every other
+    # field in the message (heart rate, cadence, power, ...) is walked past
+    # via its declared size without being interpreted.
+    def self.extract_record(data, offset, definition)
+      lat = lon = altitude = timestamp = nil
       pos = offset
 
       definition.fields.each do |field_num, size|
@@ -128,6 +131,8 @@ module Maptool
           lon = unpack_int(data, pos, size, definition.little_endian, signed: true)
         when FIELD_ALTITUDE, FIELD_ENHANCED_ALTITUDE
           altitude ||= unpack_int(data, pos, size, definition.little_endian, signed: false)
+        when FIELD_TIMESTAMP
+          timestamp = unpack_int(data, pos, size, definition.little_endian, signed: false)
         end
         pos += size
       end
@@ -136,9 +141,10 @@ module Maptool
 
       coordinate = [lon * SEMICIRCLE_TO_DEGREES, lat * SEMICIRCLE_TO_DEGREES]
       coordinate << (altitude / 5.0 - 500) if altitude && !invalid?(altitude, 2) && !invalid?(altitude, 4)
-      coordinate
+      time = Time.at(FIT_EPOCH + timestamp).utc if timestamp && !invalid?(timestamp, 4)
+      [coordinate, time]
     end
-    private_class_method :extract_point
+    private_class_method :extract_record
 
     UNPACK_FORMATS = {
       [1, true] => "c", [1, false] => "C",
diff --git a/lib/maptool/gpx.rb b/lib/maptool/gpx.rb
index 81f281d..b60ea17 100644
--- a/lib/maptool/gpx.rb
+++ b/lib/maptool/gpx.rb
@@ -1,4 +1,6 @@
 require "rexml/document"
+require "time"
+require_relative "track_stats"
 
 module Maptool
   # Converts a GPX file to a GeoJSON FeatureCollection: waypoints (<wpt>)
@@ -50,20 +52,35 @@ module Maptool
 
     def self.track_feature(trk)
       lines = []
+      all_points = []
+      times = []
       trk.each_element("trkseg") do |seg|
         points = []
-        seg.each_element("trkpt") { |pt| points << coordinate(pt) }
+        seg.each_element("trkpt") do |pt|
+          point = coordinate(pt)
+          points << point
+          all_points << point
+          times << parse_time(child_text(pt, "time"))
+        end
         lines << points unless points.empty?
       end
 
       {
         "type" => "Feature",
         "geometry" => { "type" => "MultiLineString", "coordinates" => lines },
-        "properties" => { "kind" => "track", "name" => child_text(trk, "name") },
+        "properties" => { "kind" => "track", "name" => child_text(trk, "name") }
+          .merge(TrackStats.compute(all_points, times: times)),
       }
     end
     private_class_method :track_feature
 
+    def self.parse_time(text)
+      text && Time.parse(text)
+    rescue ArgumentError
+      nil
+    end
+    private_class_method :parse_time
+
     def self.coordinate(point_el)
       lat = point_el.attributes["lat"].to_f
       lon = point_el.attributes["lon"].to_f
diff --git a/lib/maptool/track_stats.rb b/lib/maptool/track_stats.rb
new file mode 100644
index 0000000..6c70b74
--- /dev/null
+++ b/lib/maptool/track_stats.rb
@@ -0,0 +1,66 @@
+module Maptool
+  # Distance/elevation-gain/duration for a track, shared by Gpx and Fit so
+  # neither has its own copy of the haversine formula.
+  module TrackStats
+    EARTH_RADIUS_METERS = 6_371_000
+
+    # `coordinates`: array of [lon, lat] or [lon, lat, ele]. `times`: a
+    # parallel array of Time (or nil where unknown) — only its first and
+    # last non-nil entries matter, so gaps in the middle are fine.
+    def self.compute(coordinates, times: [])
+      distance = 0.0
+      elevation_gain = 0.0
+
+      coordinates.each_cons(2) do |(lon1, lat1, ele1), (lon2, lat2, ele2)|
+        distance += haversine(lat1, lon1, lat2, lon2)
+        elevation_gain += ele2 - ele1 if ele1 && ele2 && ele2 > ele1
+      end
+
+      known_times = times.compact
+      duration = known_times.size >= 2 ? (known_times.last - known_times.first).to_i : nil
+
+      {
+        "distance_meters" => distance.round(1),
+        "elevation_gain_meters" => elevation_gain.positive? ? elevation_gain.round(1) : nil,
+        "duration_secs" => duration,
+        "point_count" => coordinates.size,
+      }
+    end
+
+    def self.haversine(lat1, lon1, lat2, lon2)
+      rad = Math::PI / 180
+      dlat = (lat2 - lat1) * rad
+      dlon = (lon2 - lon1) * rad
+      a = (Math.sin(dlat / 2)**2) + (Math.cos(lat1 * rad) * Math.cos(lat2 * rad) * (Math.sin(dlon / 2)**2))
+      2 * EARTH_RADIUS_METERS * Math.asin(Math.sqrt(a))
+    end
+    private_class_method :haversine
+  end
+end
+
+if __FILE__ == $0
+  # A right-angle path with a known leg length (via the equirectangular
+  # approximation, accurate at small scale) plus a climb-then-descend
+  # elevation profile, so both distance and elevation-gain have a value to
+  # check against instead of just "did it run".
+  square = [
+    [17.0, 48.0, 100],
+    [17.001, 48.0, 150], # +50m gain
+    [17.001, 48.001, 120], # descent, no gain added
+  ]
+  stats = Maptool::TrackStats.compute(square, times: [Time.utc(2026, 1, 1, 0, 0, 0), nil, Time.utc(2026, 1, 1, 0, 10, 0)])
+
+  raise "expected nonzero distance" unless stats["distance_meters"] > 100
+  raise "expected elevation gain 50" unless stats["elevation_gain_meters"] == 50.0
+  raise "expected duration 600s" unless stats["duration_secs"] == 600
+  raise "expected point count 3" unless stats["point_count"] == 3
+
+  flat = Maptool::TrackStats.compute([[17.0, 48.0], [17.0, 48.0]], times: [])
+  raise "expected nil elevation gain without elevation data" unless flat["elevation_gain_meters"].nil?
+  raise "expected nil duration without times" unless flat["duration_secs"].nil?
+
+  single = Maptool::TrackStats.compute([[17.0, 48.0]])
+  raise "expected zero distance for a single point" unless single["distance_meters"] == 0.0
+
+  puts "ok"
+end
diff --git a/public/js/gpx.js b/public/js/gpx.js
index 2e9827f..d98c55a 100644
--- a/public/js/gpx.js
+++ b/public/js/gpx.js
@@ -304,6 +304,7 @@ export class GpxPanelControl {
     });
 
     this._registerPointInteractivity(`${id}-points`);
+    this._registerLineInteractivity(`${id}-line`);
   }
 
   // Registered once per layer id, ever — map.on(type, layerId, fn) is a
@@ -330,6 +331,30 @@ export class GpxPanelControl {
     });
   }
 
+  // Hover rather than click: unlike a waypoint, a track's properties
+  // (distance, elevation gain, duration) describe the whole line, not
+  // whatever point along it happens to get clicked.
+  _registerLineInteractivity(layerId) {
+    if (this._interactiveLayers.has(layerId)) return;
+    this._interactiveLayers.add(layerId);
+
+    let popup = null;
+    this._map.on("mouseenter", layerId, (event) => {
+      this._map.getCanvas().style.cursor = "pointer";
+      const feature = event.features[0];
+      if (!feature) return;
+      popup = new Popup({ closeButton: false, closeOnClick: false, maxWidth: "260px" })
+        .setLngLat(event.lngLat)
+        .setHTML(trackPopupHtml(feature.properties))
+        .addTo(this._map);
+    });
+    this._map.on("mouseleave", layerId, () => {
+      this._map.getCanvas().style.cursor = "";
+      popup?.remove();
+      popup = null;
+    });
+  }
+
   _removeLayers(path) {
     const id = sourceId(path);
     [`${id}-line`, `${id}-points`].forEach((layerId) => {
@@ -462,6 +487,26 @@ function popupHtml({ name, description, time }) {
   return parts.length > 0 ? parts.join("") : "<em>No details</em>";
 }
 
+// properties come straight from an uploaded GPX/FIT file — untrusted input.
+function trackPopupHtml({ name, distance_meters, elevation_gain_meters, duration_secs }) {
+  const parts = [];
+  if (name) parts.push(`<strong>${escapeHtml(name)}</strong>`);
+
+  const stats = [];
+  if (typeof distance_meters === "number") stats.push(`${(distance_meters / 1000).toFixed(1)} km`);
+  if (typeof elevation_gain_meters === "number") stats.push(`↑ ${Math.round(elevation_gain_meters)} m`);
+  if (typeof duration_secs === "number") stats.push(formatDuration(duration_secs));
+  if (stats.length > 0) parts.push(`<p>${stats.join(" · ")}</p>`);
+
+  return parts.length > 0 ? parts.join("") : "<em>No details</em>";
+}
+
+function formatDuration(totalSeconds) {
+  const hours = Math.floor(totalSeconds / 3600);
+  const minutes = Math.floor((totalSeconds % 3600) / 60);
+  return hours > 0 ? `${hours}h ${minutes}m` : `${minutes}m`;
+}
+
 function escapeHtml(text) {
   const div = document.createElement("div");
   div.textContent = text;