diff --git a/crates/ruff_metrics/src/json.rs b/crates/ruff_metrics/src/json.rs
index 2bf589240b..cb6eee4b8e 100644
--- a/crates/ruff_metrics/src/json.rs
+++ b/crates/ruff_metrics/src/json.rs
@@ -43,7 +43,12 @@ impl JsonRecorder {
             .to_str()
             .unwrap()
             .to_string();
-        let storage = PrerenderedAtomicStorage { dest, executable };
+        let start = SystemTime::now();
+        let storage = PrerenderedAtomicStorage {
+            dest,
+            executable,
+            start,
+        };
         let registry = Registry::new(storage);
         JsonRecorder { registry }
     }
@@ -74,6 +79,7 @@ impl Recorder for JsonRecorder {
 struct PrerenderedAtomicStorage {
     dest: Arc<Mutex<dyn Write + Send>>,
     executable: String,
+    start: SystemTime,
 }
 
 impl Storage<Key> for PrerenderedAtomicStorage {
@@ -82,15 +88,30 @@ impl Storage<Key> for PrerenderedAtomicStorage {
     type Histogram = Arc<Metric>;
 
     fn counter(&self, key: &Key) -> Self::Counter {
-        Arc::new(Metric::new(self.executable.clone(), key, self.dest.clone()))
+        Arc::new(Metric::new(
+            self.executable.clone(),
+            self.start,
+            key,
+            self.dest.clone(),
+        ))
     }
 
     fn gauge(&self, key: &Key) -> Self::Gauge {
-        Arc::new(Metric::new(self.executable.clone(), key, self.dest.clone()))
+        Arc::new(Metric::new(
+            self.executable.clone(),
+            self.start,
+            key,
+            self.dest.clone(),
+        ))
     }
 
     fn histogram(&self, key: &Key) -> Self::Histogram {
-        Arc::new(Metric::new(self.executable.clone(), key, self.dest.clone()))
+        Arc::new(Metric::new(
+            self.executable.clone(),
+            self.start,
+            key,
+            self.dest.clone(),
+        ))
     }
 }
 
@@ -100,11 +121,17 @@ struct Metric {
     /// having to re-render the information about the metrics key.)
     name_and_labels: String,
     dest: Arc<Mutex<dyn Write + Send>>,
+    start: SystemTime,
     value: AtomicU64,
 }
 
 impl Metric {
-    fn new(executable: String, key: &Key, dest: Arc<Mutex<dyn Write + Send>>) -> Metric {
+    fn new(
+        executable: String,
+        start: SystemTime,
+        key: &Key,
+        dest: Arc<Mutex<dyn Write + Send>>,
+    ) -> Metric {
         let mut json = Map::default();
         json.insert("executable".to_string(), executable.into());
         json.insert("key".to_string(), key.name().into());
@@ -118,6 +145,7 @@ impl Metric {
         Metric {
             name_and_labels,
             dest,
+            start,
             value: AtomicU64::default(),
         }
     }
@@ -138,6 +166,14 @@ impl Metric {
             if let Ok(timestamp) = SystemTime::now().duration_since(UNIX_EPOCH) {
                 write!(&mut buffer, ",\"timestamp\":{}", timestamp.as_secs_f64()).unwrap();
             }
+            if let Ok(since_start) = SystemTime::now().duration_since(self.start) {
+                write!(
+                    &mut buffer,
+                    ",\"since_start\":{}",
+                    since_start.as_secs_f64()
+                )
+                .unwrap();
+            }
             f(&mut buffer);
             buffer.push_str("}\n");
             let _ = self.dest.lock().unwrap().write(buffer.as_bytes());