diff --git a/src/features/greeks.py b/src/features/greeks.py
index e7cf6c5..ae7adfa 100644
--- a/src/features/greeks.py
+++ b/src/features/greeks.py
@@ -236,31 +236,33 @@ def estimate_iv(self, symbol: str, days: int = 30) -> float:
             else:
                 base_vol = 0.30  # General stocks
 
-            # Add some randomness to simulate market conditions
-            import time
-            import random
-            random.seed(int(time.time()) % 100)
-            adjustment = random.uniform(0.8, 1.2)
-
-            return base_vol * adjustment
+            # Deterministic estimate: return the per-category base volatility.
+            # Previously this was multiplied by a wall-clock-seeded random factor
+            # (random.seed(int(time.time()) % 100)), so the same symbol returned
+            # different IVs on consecutive calls and no Greek or POP derived from
+            # it was reproducible.
+            return base_vol
 
         except Exception:
             # Fallback to 30% volatility
             return 0.30
 
-    def get_iv_for_position(self, position: Position) -> List[float]:
+    def get_iv_for_position(self, position: Position, symbol: Optional[str] = None) -> List[float]:
         """
         Get IV estimates for all legs of a position.
 
         Args:
             position: Position to estimate IV for
+            symbol: Underlying symbol, when known, used to pick the base IV
 
         Returns:
             List of IV estimates for each leg
         """
-        # In a real implementation, this would fetch option chain data
-        # For now, use the same IV for all legs with slight variations
-        base_iv = self.estimate_iv("SPY")  # Use SPY as base
+        # In a real implementation, this would fetch option chain data.
+        # Use the underlying symbol when the caller knows it. Without it, assume
+        # a general single-stock volatility rather than SPY (a low-vol ETF),
+        # which previously underestimated IV for every individual name.
+        base_iv = self.estimate_iv(symbol) if symbol else self.estimate_iv("UNKNOWN")
 
         iv_estimates = []
         for i, (strike, option_type) in enumerate(zip(position.strikes, position.option_types)):
diff --git a/tests/test_greeks.py b/tests/test_greeks.py
index 860460c..42585ce 100644
--- a/tests/test_greeks.py
+++ b/tests/test_greeks.py
@@ -135,6 +135,16 @@ def test_iv_estimation(self):
         self.assertGreater(iv, 0.05)
         self.assertLess(iv, 1.0)
 
+    def test_iv_estimation_is_deterministic(self):
+        """estimate_iv must return the same value on repeated calls (issue #9)."""
+        first = self.iv_estimator.estimate_iv('AAPL')
+        second = self.iv_estimator.estimate_iv('AAPL')
+        self.assertEqual(first, second)
+        # And distinct symbol categories get distinct, stable bases.
+        self.assertEqual(self.iv_estimator.estimate_iv('SPY'), 0.15)
+        self.assertEqual(self.iv_estimator.estimate_iv('AAPL'), 0.25)
+        self.assertEqual(self.iv_estimator.estimate_iv('XYZ'), 0.30)
+
     def test_position_iv_estimation(self):
         """Test position-level IV estimation."""
         position = Position(