diff --git a/src/db/migrations/004_sentry_sdk_init.sql b/src/db/migrations/004_sentry_sdk_init.sql
new file mode 100644
index 0000000..785904c
--- /dev/null
+++ b/src/db/migrations/004_sentry_sdk_init.sql
@@ -0,0 +1,11 @@
+-- Sentry SDK init duration, sourced from the test app's User Timing API.
+--
+-- The instrumented apps emit a `performance.measure('sentry-sdk-init-duration')`
+-- spanning SDK initialisation. Lighthouse surfaces it in the `user-timings`
+-- audit, and the worker denormalises the measure's duration here (like the
+-- other scalar metrics) so the publisher can ship it to Sentry.
+--
+-- NULL means the measure was absent from the run (e.g. no-sentry cells, or the
+-- mark fired after Lighthouse's trace window closed).
+
+ALTER TABLE runs ADD COLUMN sentry_sdk_init_ms INTEGER;
diff --git a/src/publisher/runner.js b/src/publisher/runner.js
index b11f9c7..e306dca 100644
--- a/src/publisher/runner.js
+++ b/src/publisher/runner.js
@@ -88,7 +88,7 @@ function pickUnpublishedCells() {
 function loadRunsForCell(cellId) {
   return getDb().prepare(`
     SELECT run_id, run_index, performance_score, lcp_ms, fcp_ms, tbt_ms,
-           cls, total_bytes, collected_at
+           cls, total_bytes, sentry_sdk_init_ms, collected_at
       FROM runs WHERE cell_id = ? ORDER BY run_index
   `).all(cellId);
 }
@@ -147,6 +147,11 @@ function emitRunMetrics(run, baseAttrs) {
   // to a string-typed field and refuse to compute p50/p90 over it. Score
   // and CLS therefore both go through the numeric path below.
 
+  // collect number of runs as a metric (only as attributes doesn't allow for visualization in Sentry)
+  Sentry.metrics.count('lighthouse.run.completed', 1, {
+    attributes: attrs,
+  });
+
   if (run.performance_score != null) {
     // LHR scores are 0..1 floats; Lighthouse's own UI shows them as 0..100.
     // We multiply here so Sentry dashboards render '78%' instead of '0.78'
@@ -188,4 +193,13 @@ function emitRunMetrics(run, baseAttrs) {
       attributes: attrs,
     });
   }
+  if (run.sentry_sdk_init_ms != null) {
+    // `performance.measure('sentry-sdk-init-duration')` from the instrumented
+    // test app, surfaced by Lighthouse's user-timings audit. Null for
+    // no-sentry cells, so the dashboard only sees it where it's meaningful.
+    Sentry.metrics.distribution('lighthouse.sentry_sdk_init', run.sentry_sdk_init_ms, {
+      unit: 'millisecond',
+      attributes: attrs,
+    });
+  }
 }
diff --git a/src/worker/lighthouse.js b/src/worker/lighthouse.js
index f3c34cf..aea2908 100644
--- a/src/worker/lighthouse.js
+++ b/src/worker/lighthouse.js
@@ -109,5 +109,19 @@ export function extractMetrics(lhr) {
     tbtMs: round(audit('total-blocking-time')),
     cls: audit('cumulative-layout-shift'),
     bytes: round(audit('total-byte-weight')),
+    sentrySdkInitMs: round(userTimingMeasure(lhr, 'sentry-sdk-init-duration')),
   };
 }
+
+/**
+ * Pull a single `performance.measure()` duration (ms) out of Lighthouse's
+ * `user-timings` audit by name. Returns null if the measure isn't present —
+ * which happens for no-sentry cells, or if the measure fired after the trace
+ * window closed. Only `timingType: 'Measure'` entries carry a duration; marks
+ * are ignored.
+ */
+function userTimingMeasure(lhr, name) {
+  const items = lhr?.audits?.['user-timings']?.details?.items ?? [];
+  const measure = items.find(i => i.name === name && i.timingType === 'Measure');
+  return measure?.duration ?? null;
+}
diff --git a/src/worker/runner.js b/src/worker/runner.js
index 76d2eab..351607b 100644
--- a/src/worker/runner.js
+++ b/src/worker/runner.js
@@ -226,8 +226,9 @@ function writeRunsToDb({ cell, persisted }) {
     INSERT INTO runs (
       run_id, cell_id, run_index, is_representative,
       performance_score, lcp_ms, fcp_ms, tbt_ms, cls, total_bytes,
+      sentry_sdk_init_ms,
       lhr_json_path, report_html_path, collected_at
-    ) VALUES (?, ?, ?, 0, ?, ?, ?, ?, ?, ?, ?, ?, ?)
+    ) VALUES (?, ?, ?, 0, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)
   `);
   const completedIso = new Date().toISOString();
 
@@ -237,6 +238,7 @@ function writeRunsToDb({ cell, persisted }) {
         r.runId, cell.cell_id, r.runIndex,
         r.metrics.score, r.metrics.lcpMs, r.metrics.fcpMs, r.metrics.tbtMs,
         r.metrics.cls, r.metrics.bytes,
+        r.metrics.sentrySdkInitMs,
         r.jsonPath, r.htmlPath, completedIso,
       );
     }