diff --git a/Cargo.lock b/Cargo.lock
index e3c5696e..d27868a4 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -4383,6 +4383,7 @@ version = "0.1.0"
 dependencies = [
  "bevy",
  "half",
+ "serde_json",
  "skate-core",
  "skate-data",
 ]
diff --git a/crates/skate-game/Cargo.toml b/crates/skate-game/Cargo.toml
index 709c3d7e..aba17f63 100644
--- a/crates/skate-game/Cargo.toml
+++ b/crates/skate-game/Cargo.toml
@@ -9,3 +9,4 @@ bevy.workspace = true
 skate-core.workspace = true
 skate-data.workspace = true
 half = "=2.7.1"
+serde_json.workspace = true
diff --git a/crates/skate-game/src/app.rs b/crates/skate-game/src/app.rs
index f19c2b3d..64b4106e 100644
--- a/crates/skate-game/src/app.rs
+++ b/crates/skate-game/src/app.rs
@@ -95,6 +95,7 @@ pub(crate) fn build(
         world::WorldPlugin,
         camera::CameraPlugin,
         verification::VerificationPlugin,
+        crate::performance::PerformancePlugin,
     ));
     app
 }
diff --git a/crates/skate-game/src/main.rs b/crates/skate-game/src/main.rs
index 5923cd48..7d4ae50b 100644
--- a/crates/skate-game/src/main.rs
+++ b/crates/skate-game/src/main.rs
@@ -10,6 +10,7 @@ mod input;
 mod physics;
 mod skater_animation;
 mod verification;
+mod performance;
 mod world;
 mod skate_world;
 
diff --git a/crates/skate-game/src/performance.rs b/crates/skate-game/src/performance.rs
new file mode 100644
index 00000000..bbd23e1e
--- /dev/null
+++ b/crates/skate-game/src/performance.rs
@@ -0,0 +1,103 @@
+//! Opt-in repeatable frame/physics timing: SKATE_PERF_REPORT=path.json.
+use bevy::prelude::*;
+use std::{path::PathBuf, time::Instant};
+use std::sync::{Arc, Mutex};
+use bevy::render::{Render, RenderApp, RenderSystems};
+
+#[derive(Resource)]
+pub(crate) struct Performance {
+    path: PathBuf,
+    start: Option<Instant>,
+    frame_start: Instant,
+    previous: Instant,
+    physics_ms: f64,
+    ticks: u32,
+    samples: Vec<[f64; 4]>,
+    render: Arc<Mutex<Vec<[f64; 2]>>>,
+}
+impl Performance {
+    pub(crate) fn physics(&mut self, elapsed: std::time::Duration) {
+        self.physics_ms += elapsed.as_secs_f64() * 1000.;
+        self.ticks += 1;
+    }
+}
+
+pub(crate) struct PerformancePlugin;
+impl Plugin for PerformancePlugin {
+    fn build(&self, app: &mut App) {
+        let Some(path) = std::env::var_os("SKATE_PERF_REPORT") else { return; };
+        let now = Instant::now();
+        let render = Arc::new(Mutex::new(Vec::new()));
+        if let Some(render_app) = app.get_sub_app_mut(RenderApp) {
+            render_app.insert_resource(RenderPerformance { start: None, frame: now, prepared: now, samples: render.clone() })
+                .add_systems(Render, render_begin.before(RenderSystems::ExtractCommands))
+                .add_systems(Render, render_prepared.after(RenderSystems::Prepare).before(RenderSystems::Render))
+                .add_systems(Render, render_finish.after(RenderSystems::PostCleanup));
+        }
+        // Benchmark measurements must not depend on whether the window has focus.
+        app.insert_resource(bevy::winit::WinitSettings::continuous());
+        app.insert_resource(Performance {
+            path: path.into(), start: None, frame_start: now, previous: now,
+            physics_ms: 0., ticks: 0, samples: Vec::new(), render,
+        }).add_systems(First, begin).add_systems(Last, finish);
+    }
+}
+fn begin(mut p: ResMut<Performance>) {
+    p.frame_start = Instant::now();
+    p.physics_ms = 0.;
+    p.ticks = 0;
+}
+fn finish(mut p: ResMut<Performance>, mut exit: MessageWriter<AppExit>) {
+    let now = Instant::now();
+    let elapsed = now.duration_since(*p.start.get_or_insert(now)).as_secs_f64();
+    let frame = now.duration_since(p.previous).as_secs_f64() * 1000.;
+    p.previous = now;
+    // Exclude initialization and shader warmup. Frame interval includes render
+    // synchronization; CPU schedule time is First..Last of the main world.
+    if elapsed > 10. {
+        let sample = [frame, now.duration_since(p.frame_start).as_secs_f64() * 1000., p.physics_ms, f64::from(p.ticks)];
+        p.samples.push(sample);
+    }
+    if elapsed > 25. && !p.samples.is_empty() {
+        let mean = |column: usize| p.samples.iter().map(|s| s[column]).sum::<f64>() / p.samples.len() as f64;
+        let mut frames: Vec<_> = p.samples.iter().map(|s| s[0]).collect();
+        frames.sort_by(f64::total_cmp);
+        let render = p.render.lock().unwrap();
+        let render_mean = |column: usize| render.iter().map(|s| s[column]).sum::<f64>() / render.len().max(1) as f64;
+        let report = serde_json::json!({
+            "frames": frames.len(), "fps": 1000. / mean(0),
+            "frame_ms_mean": mean(0), "frame_ms_median": frames[frames.len()/2],
+            "frame_ms_p95": frames[(frames.len()-1)*95/100],
+            "main_schedule_ms_mean": mean(1), "physics_ms_per_frame": mean(2),
+            "physics_ticks_per_frame": mean(3),
+            "physics_ms_per_tick": mean(2) / mean(3).max(f64::EPSILON),
+            "render_prepare_ms_mean": render_mean(0), "render_submit_ms_mean": render_mean(1),
+            "samples": p.samples,
+        });
+        match std::fs::write(&p.path, serde_json::to_vec_pretty(&report).unwrap()) {
+            Ok(()) => { eprintln!("SKATE_PERF_REPORT {}", p.path.display()); exit.write(AppExit::Success); }
+            Err(e) => { eprintln!("Performance report: {e}"); exit.write(AppExit::error()); }
+        }
+    }
+}
+
+#[derive(Resource)]
+struct RenderPerformance {
+    start: Option<Instant>, frame: Instant, prepared: Instant,
+    samples: Arc<Mutex<Vec<[f64; 2]>>>,
+}
+fn render_begin(mut p: ResMut<RenderPerformance>) {
+    p.frame = Instant::now();
+}
+fn render_prepared(mut p: ResMut<RenderPerformance>) {
+    p.prepared = Instant::now();
+}
+fn render_finish(mut p: ResMut<RenderPerformance>) {
+    let now = Instant::now();
+    if now.duration_since(*p.start.get_or_insert(now)).as_secs_f64() > 10. {
+        p.samples.lock().unwrap().push([
+            p.prepared.duration_since(p.frame).as_secs_f64() * 1000.,
+            now.duration_since(p.prepared).as_secs_f64() * 1000.,
+        ]);
+    }
+}
diff --git a/crates/skate-game/src/physics.rs b/crates/skate-game/src/physics.rs
index ec6a6b28..8a395b63 100644
--- a/crates/skate-game/src/physics.rs
+++ b/crates/skate-game/src/physics.rs
@@ -205,10 +205,12 @@ fn advance(
     mut camera: ResMut<crate::camera::CameraRuntime>,
     mut cadence: ResMut<Time<Fixed>>,
     mut exit: MessageWriter<AppExit>,
+    mut performance: Option<ResMut<crate::performance::Performance>>,
 ) {
     if physics.failed {
         return;
     }
+    let timer = performance.as_ref().map(|_| std::time::Instant::now());
     let mut actions = input.player_actions();
     let input_available = input
         .status
@@ -239,6 +241,9 @@ fn advance(
         exit.write(AppExit::error());
     }
     cadence.set_timestep(physics.clock.period());
+    if let (Some(performance), Some(timer)) = (performance.as_mut(), timer) {
+        performance.physics(timer.elapsed());
+    }
 }
 
 impl GamePhysics {