diff --git a/.jules/bolt.md b/.jules/bolt.md
index d54cf10f..c9e5b63e 100644
--- a/.jules/bolt.md
+++ b/.jules/bolt.md
@@ -61,3 +61,7 @@
 ## 2026-07-13 - Array.from mapping optimization
 **Learning:** Using `Array.from({ length: N }).map(...)` creates an intermediate array of `undefined` values which requires memory allocation and garbage collection, adding O(N) unnecessary overhead in frequently re-rendered UI components.
 **Action:** Use `Array.from({ length: N }, (_, index) => ...)` to map elements directly during array creation, avoiding intermediate allocations.
+
+## 2026-07-14 - O(N) iteration with reduced function overhead for finding maximum values
+**Learning:** Using `Array.prototype.reduce()` coupled with `Math.max()` to find the maximum value in a large array (like transcription notes) introduces significant function call overhead, allocating intermediate closures for each item.
+**Action:** Prefer standard `for` loops with simple reassignment over `.reduce()` for finding extreme values in performance-critical paths, especially for arrays that can grow very large.
diff --git a/apps/desktop/src/features/workspace/GrooveMap.tsx b/apps/desktop/src/features/workspace/GrooveMap.tsx
index 2745d4d7..2defcdd0 100644
--- a/apps/desktop/src/features/workspace/GrooveMap.tsx
+++ b/apps/desktop/src/features/workspace/GrooveMap.tsx
@@ -17,7 +17,14 @@ function GrooveMapComponent({ notes, isLoading }: GrooveMapProps) {
 
   // Find max offset to determine timeline width
   const maxTime = useMemo(() => {
-    return renderedNotes.reduce((max, n) => Math.max(max, n.offset), 10);
+    // Performance: Avoid function call overhead of .reduce() and Math.max for large arrays
+    let max = 10;
+    for (let i = 0; i < renderedNotes.length; i++) {
+      if (renderedNotes[i].offset > max) {
+        max = renderedNotes[i].offset;
+      }
+    }
+    return max;
   }, [renderedNotes]);
 
   // Unique pitches to determine vertical lanes (avoiding 88-key piano roll)