diff --git a/src/components/EmailBodyView.tsx b/src/components/EmailBodyView.tsx
index addfc435..bc2068f9 100644
--- a/src/components/EmailBodyView.tsx
+++ b/src/components/EmailBodyView.tsx
@@ -19,7 +19,7 @@ import { useContactsStore } from '../stores/contacts-store';
 import { useLocaleStore } from '../stores/locale-store';
 import { spacing, typography, type ThemePalette } from '../theme/tokens';
 import { useColors, useResolvedTheme } from '../theme/colors';
-import { perfEndAfterPaint } from '../lib/perf-marks';
+import { perfEndAfterPaint, perfLap } from '../lib/perf-marks';
 import type { RootStackParamList } from '../navigation/types';
 
 type Nav = NativeStackNavigationProp<RootStackParamList>;
@@ -684,6 +684,9 @@ export default function EmailBodyView({
     [prepared.isHtml, prepared.applyInversion, quoteLabels],
   );
 
+  // Performance harness: how much of opening a message is the WebView.
+  React.useEffect(() => { perfLap('open-message', 'body-mounted'); }, []);
+
   const onMessage = (e: WebViewMessageEvent) => {
     const data = e.nativeEvent.data;
     // The body reported its size: it is laid out (performance harness).
@@ -791,6 +794,7 @@ export default function EmailBodyView({
           injectedJavaScript={injectedJs}
           onMessage={onMessage}
           onLoadEnd={() => {
+            perfLap('open-message', 'webview-loaded');
             // A (re)load resets the page's zoom state to 1 — drop any host-side
             // scroll locks so they can't go stale (e.g. cid images arriving
             // reload the source mid-zoom).
diff --git a/src/lib/perf-marks.ts b/src/lib/perf-marks.ts
index 3bcbeadd..6fb3cdc4 100644
--- a/src/lib/perf-marks.ts
+++ b/src/lib/perf-marks.ts
@@ -46,6 +46,14 @@ export function perfEnd(name: string, detail?: Record<string, string | number |
   perfMark(name, { ms: Date.now() - t0, ...detail });
 }
 
+/** Log how far into a running span a step got, without ending it. */
+export function perfLap(name: string, lap: string): void {
+  if (!enabled) return;
+  const t0 = started.get(name);
+  if (t0 === undefined) return;
+  perfMark(`${name}:${lap}`, { ms: Date.now() - t0 });
+}
+
 /**
  * End a span once the next frames are drawn: two animation frames after the
  * state change that rendered the result, so the time includes commit and