diff --git a/apps/web/src/routes/internal.ts b/apps/web/src/routes/internal.ts
index 2834e31..0b150c0 100644
--- a/apps/web/src/routes/internal.ts
+++ b/apps/web/src/routes/internal.ts
@@ -22,11 +22,15 @@ export const internal = new Elysia({ prefix: "/internal", detail: { hide: true }
     return {};
   })
 
-  // Returns monitors that are due for a check, with scheduled_at = now()
+  // Returns monitors that are due for a check.
+  // scheduled_at = last_checked_at + interval_s (ideal fire time), so jitter = actual_start - scheduled_at
   .get("/due", async () => {
-    const scheduled_at = new Date().toISOString();
     const monitors = await sql`
-      SELECT m.id, m.url, m.method, m.request_headers, m.request_body, m.timeout_ms, m.interval_s, m.query
+      SELECT m.id, m.url, m.method, m.request_headers, m.request_body, m.timeout_ms, m.interval_s, m.query,
+             CASE
+               WHEN last.checked_at IS NULL THEN now()
+               ELSE last.checked_at + (m.interval_s || ' seconds')::interval
+             END AS scheduled_at
       FROM monitors m
       LEFT JOIN LATERAL (
         SELECT checked_at FROM pings
@@ -37,8 +41,7 @@ export const internal = new Elysia({ prefix: "/internal", detail: { hide: true }
         AND (last.checked_at IS NULL
           OR last.checked_at < now() - (m.interval_s || ' seconds')::interval)
     `;
-    // Attach scheduled_at to each monitor so the runner can report jitter
-    return monitors.map((m: any) => ({ ...m, scheduled_at }));
+    return monitors;
   })
 
   // Manual retention cleanup trigger