diff --git a/lib/ocaml/baseline/expected.json b/lib/ocaml/baseline/expected.json
index 209ee3f4..03ab6707 100644
--- a/lib/ocaml/baseline/expected.json
+++ b/lib/ocaml/baseline/expected.json
@@ -59,6 +59,7 @@
   "grid_paths.ml": 210,
   "group_consec.ml": 53,
   "hailstone.ml": 111,
+  "harshad.ml": 33,
   "hamming.ml": 4,
   "hanoi.ml": 1023,
   "hist.ml": 75,
diff --git a/lib/ocaml/baseline/harshad.ml b/lib/ocaml/baseline/harshad.ml
new file mode 100644
index 00000000..cff87551
--- /dev/null
+++ b/lib/ocaml/baseline/harshad.ml
@@ -0,0 +1,19 @@
+let digit_sum n =
+  let m = ref n in
+  let s = ref 0 in
+  while !m > 0 do
+    s := !s + !m mod 10;
+    m := !m / 10
+  done;
+  !s
+
+let count_harshad limit =
+  let c = ref 0 in
+  for n = 1 to limit do
+    if n mod (digit_sum n) = 0 then c := !c + 1
+  done;
+  !c
+
+;;
+
+count_harshad 100
diff --git a/plans/ocaml-on-sx.md b/plans/ocaml-on-sx.md
index 993a5dab..e121528e 100644
--- a/plans/ocaml-on-sx.md
+++ b/plans/ocaml-on-sx.md
@@ -407,6 +407,12 @@ _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.
+- 2026-05-10 Phase 5.1 — harshad.ml baseline (count Niven/Harshad
+  numbers ≤ 100 = 33). A Harshad number is divisible by its digit
+  sum. All single-digit numbers qualify trivially (9). Plus 10, 12,
+  18, 20, 21, 24, 27, 30, 36, 40, 42, 45, 48, 50, 54, 60, 63, 70,
+  72, 80, 81, 84, 90, 100 (24 more) = 33 under 100. 133 baseline
+  programs total.
 - 2026-05-10 Phase 5.1 — reverse_int.ml baseline (digit-reverse,
   reverse(12345) + reverse(100) + reverse(7) = 54321 + 1 + 7 =
   54329). Walks digits via mod 10 / div 10, accumulating the