diff --git a/lib/ocaml/baseline/count_palindromes.ml b/lib/ocaml/baseline/count_palindromes.ml
new file mode 100644
index 00000000..ac02792c
--- /dev/null
+++ b/lib/ocaml/baseline/count_palindromes.ml
@@ -0,0 +1,17 @@
+let count_pal s =
+  let n = String.length s in
+  let count = ref 0 in
+  for c = 0 to 2 * n - 2 do
+    let l = ref (c / 2) in
+    let r = ref ((c + 1) / 2) in
+    while !l >= 0 && !r < n && s.[!l] = s.[!r] do
+      count := !count + 1;
+      l := !l - 1;
+      r := !r + 1
+    done
+  done;
+  !count
+
+;;
+
+count_pal "aabaa"
diff --git a/lib/ocaml/baseline/expected.json b/lib/ocaml/baseline/expected.json
index 76cc379e..81064fe6 100644
--- a/lib/ocaml/baseline/expected.json
+++ b/lib/ocaml/baseline/expected.json
@@ -32,6 +32,7 @@
   "coin_min.ml": 6,
   "count_change.ml": 406,
   "count_inversions.ml": 12,
+  "count_palindromes.ml": 9,
   "count_subarrays_k.ml": 7,
   "csv.ml": 10,
   "egg_drop.ml": 8,
diff --git a/plans/ocaml-on-sx.md b/plans/ocaml-on-sx.md
index 4ead3913..d2902e4d 100644
--- a/plans/ocaml-on-sx.md
+++ b/plans/ocaml-on-sx.md
@@ -407,6 +407,15 @@ _Newest first._
   binary search tree (`type 'a tree = Leaf | Node of 'a * 'a tree *
   'a tree`) with insert + in-order traversal. Tests parametric ADT,
   recursive match, List.append, List.fold_left.
+- 2026-05-11 Phase 5.1 — count_palindromes.ml baseline (count
+  palindromic substrings of "aabaa" = 9). Expand-around-center
+  with 2n−1 centers (n odd-length, n−1 even-length); for each,
+  walk outward while characters match and both indices in range.
+  Decomposition: c/2 and (c+1)/2 gives both odd (c even) and even
+  (c odd) starting pairs. Palindromes in "aabaa": 5 singletons
+  + 2 "aa"s + 1 "aba" + 1 "aabaa" = 9. Complements lps_dp.ml
+  (longest subsequence) and manacher.ml (longest substring); this
+  one counts ALL palindromic substrings. 187 baseline programs total.
 - 2026-05-11 Phase 5.1 — count_subarrays_k.ml baseline (count
   contiguous subarrays of [1;1;1;2;-1;3;1;-2;4] summing to k=3
   = 7). Prefix-sum brute force in O(n²): build cumulative array,