diff --git a/bot/bot.py b/bot/bot.py
index 9dcd742..8b6f1cf 100644
--- a/bot/bot.py
+++ b/bot/bot.py
@@ -200,12 +200,12 @@ async def guess(self, ctx: commands.Context, word: str = "") -> None:
             await ctx.send(f"🎉 The word '{word}' was already found by {found_by}!")
         elif result.already_cited:
             if result.entry.score is not None:
-                pct = round(result.entry.score * 100)
+                pct = math.floor(result.entry.score * 100)
                 await ctx.send(f"'{word}' has already been suggested ({pct}% similarity).")
             else:
                 await ctx.send(f"'{word}' has already been suggested.")
         elif result.entry.score is not None:
-            pct = round(result.entry.score * 100)
+            pct = math.floor(result.entry.score * 100)
             await ctx.send(f"'{word}': {pct}% similarity")
         else:
             await ctx.send(f"'{word}' is not in the vocabulary.")
@@ -276,7 +276,7 @@ async def hint(self, ctx: commands.Context) -> None:
             return
 
         parts = [
-            f"{i + 1}. {e.raw_word} ({round((e.score or 0.0) * 100)}%)"
+            f"{i + 1}. {e.raw_word} ({math.floor((e.score or 0.0) * 100)}%)"
             for i, e in enumerate(top)
         ]
         await ctx.send("Top guesses: " + " | ".join(parts))
@@ -303,7 +303,7 @@ async def status(self, ctx: commands.Context) -> None:
         top = self._game_state.top_guesses(1)
         if top:
             best = top[0]
-            pct = round((best.score or 0.0) * 100)
+            pct = math.floor((best.score or 0.0) * 100)
             await ctx.send(
                 f"Game in progress. {attempts} attempt(s). "
                 f"Best guess: '{best.raw_word}' ({pct}%)."
diff --git a/game/engine.py b/game/engine.py
index bbbe985..b51edb8 100644
--- a/game/engine.py
+++ b/game/engine.py
@@ -79,23 +79,39 @@ def similarity(self, word_a: str, word_b: str) -> float | None:
     def score_guess(self, guess: str, target: str) -> float | None:
         """Score a player's guess against the target word.
 
-        Returns ``1.0`` for an exact (cleaned) match, or the cosine similarity
-        for a non-exact guess.  Returns ``None`` when either word is missing
-        from the vocabulary.
+        Returns ``1.0`` for an exact (cleaned) match, or a **percentile rank**
+        in ``[0, 1)`` for a non-exact guess.  Returns ``None`` when either
+        word is missing from the vocabulary.
+
+        The percentile rank expresses what fraction of the vocabulary is *less
+        similar* to *target* than *guess* is.  For example, a score of
+        ``0.99`` means the guess is closer to the target than 99 % of all
+        words in the model.
 
         Args:
             guess: The word submitted by the player.
             target: The secret target word.
 
         Returns:
-            A float in ``[0, 1]`` (after clamping), or ``None``.
+            A float in ``[0, 1]``, or ``None``.
         """
         if clean_word(guess) == clean_word(target):
             return 1.0
-        sim = self.similarity(guess, target)
-        if sim is None:
+        if self._model is None:
+            raise RuntimeError("Model not loaded. Call load() first.")
+        key_guess = self._cleaned_key_map.get(clean_word(guess))
+        key_target = self._cleaned_key_map.get(clean_word(target))
+        if key_guess is None or key_target is None:
+            return None
+        rank = self._model.rank(key_target, key_guess)
+        # effective_vocab excludes the target word itself, matching how
+        # gensim's closer_than() (used internally by rank()) omits key1.
+        # Guard against degenerate single-word vocabularies where no ranking
+        # is meaningful and division by zero would occur.
+        effective_vocab = len(self._model.key_to_index) - 1
+        if effective_vocab <= 0:
             return None
-        return max(0.0, min(1.0, sim))
+        return max(0.0, min(1.0, (effective_vocab - rank) / effective_vocab))
 
 
 class GameEngine:
diff --git a/overlay/static/index.html b/overlay/static/index.html
index 7d8e69e..a95ee91 100644
--- a/overlay/static/index.html
+++ b/overlay/static/index.html
@@ -192,7 +192,7 @@
     const elAttempts  = document.getElementById('attempt-count');
 
     function pct(score) {
-      return score != null ? Math.round(score * 100) : 0;
+      return score != null ? Math.floor(score * 100) : 0;
     }
 
     function barColor(score) {
diff --git a/tests/test_commands.py b/tests/test_commands.py
index 1a9bb85..ae2df39 100644
--- a/tests/test_commands.py
+++ b/tests/test_commands.py
@@ -383,11 +383,37 @@ async def test_guess_near_match_shows_similarity(self):
         message = ctx.send.call_args[0][0]
         assert "%" in message
 
-    async def test_guess_percentage_uses_rounding_not_truncation(self):
-        """Chat must show the same rounded percentage as the overlay (Math.round)."""
+    async def test_guess_percentage_uses_floor_not_round(self):
+        """Chat must use floor() so that near-100% percentiles never display as 100%.
 
-        class _RoundingScorer:
-            """Returns 0.475 so that truncation gives 47% but rounding gives 48%."""
+        A scorer returning 0.998 gives round()=100 but floor()=99; floor must be used
+        so that 100% is reserved exclusively for the exact-match win message.
+        """
+
+        class _NearHundredScorer:
+            """Returns 0.998 so that round() gives 100% but floor() gives 99%."""
+
+            def score_guess(self, guess: str, target: str) -> float | None:
+                from game.word_utils import clean_word
+                if clean_word(guess) == clean_word(target):
+                    return 1.0
+                return 0.998
+
+        bot = _make_bot(cooldown=0)
+        bot._game_state = GameState(scorer=_NearHundredScorer())
+        bot._game_state.start_new_game("chat", Difficulty.EASY)
+        ctx = _make_ctx()
+        ctx.author.name = "alice"
+        await _guess_fn(bot, ctx, "chien")
+        message = ctx.send.call_args[0][0]
+        assert "99%" in message, f"Expected 99% (floor), got: {message}"
+        assert "100%" not in message, f"100% must be reserved for exact matches, got: {message}"
+
+    async def test_guess_percentage_uses_floor_truncation(self):
+        """Floor truncates toward zero: 0.475 * 100 = 47, not 48."""
+
+        class _FloorScorer:
+            """Returns 0.475 so that floor gives 47% but round gives 48%."""
 
             def score_guess(self, guess: str, target: str) -> float | None:
                 from game.word_utils import clean_word
@@ -396,13 +422,13 @@ def score_guess(self, guess: str, target: str) -> float | None:
                 return 0.475
 
         bot = _make_bot(cooldown=0)
-        bot._game_state = GameState(scorer=_RoundingScorer())
+        bot._game_state = GameState(scorer=_FloorScorer())
         bot._game_state.start_new_game("chat", Difficulty.EASY)
         ctx = _make_ctx()
         ctx.author.name = "alice"
         await _guess_fn(bot, ctx, "chien")
         message = ctx.send.call_args[0][0]
-        assert "48%" in message, f"Expected 48% (rounded), got: {message}"
+        assert "47%" in message, f"Expected 47% (floor), got: {message}"
 
     async def test_guess_unknown_word_reports_vocabulary_miss(self):
         bot = _make_bot(cooldown=0)
diff --git a/tests/test_engine.py b/tests/test_engine.py
index fe1ca0a..13e7d8f 100644
--- a/tests/test_engine.py
+++ b/tests/test_engine.py
@@ -82,6 +82,21 @@ def test_score_is_between_zero_and_one(self):
             assert score is not None
             assert 0.0 <= score <= 1.0
 
+    def test_score_is_percentile_rank(self):
+        """score_guess returns a percentile rank, not raw cosine similarity.
+
+        With 4 words in the test vocabulary (chat, chien, maison, voiture),
+        effective_vocab = 3 (excluding the target 'chat' itself).  chien is
+        the closest non-target word (rank 1/3 → score 2/3) and maison is
+        less similar (rank 2/3 → score 1/3), so chien must outrank maison.
+        """
+        engine = _make_engine()
+        score_chien = engine.score_guess("chien", "chat")   # rank 1/3 → 2/3
+        score_maison = engine.score_guess("maison", "chat") # rank 2/3 → 1/3
+        assert score_chien is not None
+        assert score_maison is not None
+        assert score_chien > score_maison
+
     def test_unknown_word_returns_none(self):
         engine = _make_engine()
         assert engine.score_guess("inconnu", "chat") is None