diff --git a/batters/creation.py b/batters/creation.py
index a6e81a1..9f81dfc 100644
--- a/batters/creation.py
+++ b/batters/creation.py
@@ -6,7 +6,7 @@ import numpy as np
 from creation_helpers import (
     get_all_pybaseball_ids, sanitize_name, CLUB_LIST, FRANCHISE_LIST, pd_players_df,
     mlbteam_and_franchise, get_hand, NEW_PLAYER_COST, RARITY_BASE_COSTS,
-    should_update_player_description
+    should_update_player_description, calculate_rarity_cost_adjustment
 )
 from db_calls import db_post, db_get, db_put, db_patch
 from . import calcs_batter as cba
@@ -353,80 +353,13 @@ async def post_player_updates(
             ])
 
         elif df_data['rarity'] != df_data['new_rarity_id']:
-            old_rarity = df_data['rarity']
-            new_rarity = df_data['new_rarity_id']
-            old_cost = df_data['cost']
-            new_cost = 0
-
-            if old_rarity == 1:
-                if new_rarity == 2:
-                    new_cost = max(old_cost - 540, 100)
-                elif new_rarity == 3:
-                    new_cost = max(old_cost - 720, 50)
-                elif new_rarity == 4:
-                    new_cost = max(old_cost - 780, 15)
-                elif new_rarity == 5:
-                    new_cost = max(old_cost - 800, 5)
-                elif new_rarity == 99:
-                    new_cost = old_cost + 1600
-            elif old_rarity == 2:
-                if new_rarity == 1:
-                    new_cost = old_cost + 540
-                elif new_rarity == 3:
-                    new_cost = max(old_cost - 180, 50)
-                elif new_rarity == 4:
-                    new_cost = max(old_cost - 240, 15)
-                elif new_rarity == 5:
-                    new_cost = max(old_cost - 260, 5)
-                elif new_rarity == 99:
-                    new_cost = old_cost + 2140
-            elif old_rarity == 3:
-                if new_rarity == 1:
-                    new_cost = old_cost + 720
-                elif new_rarity == 2:
-                    new_cost = old_cost + 180
-                elif new_rarity == 4:
-                    new_cost = max(old_cost - 60, 15)
-                elif new_rarity == 5:
-                    new_cost = max(old_cost - 80, 5)
-                elif new_rarity == 99:
-                    new_cost = old_cost + 2320
-            elif old_rarity == 4:
-                if new_rarity == 1:
-                    new_cost = old_cost + 780
-                elif new_rarity == 2:
-                    new_cost = old_cost + 240
-                elif new_rarity == 3:
-                    new_cost = old_cost + 60
-                elif new_rarity == 5:
-                    new_cost = max(old_cost - 20, 5)
-                elif new_rarity == 99:
-                    new_cost = old_cost + 2380
-            elif old_rarity == 5:
-                if new_rarity == 1:
-                    new_cost = old_cost + 800
-                elif new_rarity == 2:
-                    new_cost = old_cost + 260
-                elif new_rarity == 3:
-                    new_cost = old_cost + 80
-                elif new_rarity == 4:
-                    new_cost = old_cost + 20
-                elif new_rarity == 99:
-                    new_cost = old_cost + 2400
-            elif old_rarity == 99:
-                if new_rarity == 1:
-                    new_cost = max(old_cost - 1600, 800)
-                elif new_rarity == 2:
-                    new_cost = max(old_cost - 2140, 100)
-                elif new_rarity == 3:
-                    new_cost = max(old_cost - 2320, 50)
-                elif new_rarity == 4:
-                    new_cost = max(old_cost - 2380, 15)
-                elif new_rarity == 5:
-                    new_cost = max(old_cost - 2400, 5)
-
-            if new_cost != 0:
-                params.extend([('cost', new_cost), ('rarity_id', new_rarity)])
+            # Calculate adjusted cost for rarity change using lookup table
+            new_cost = calculate_rarity_cost_adjustment(
+                old_rarity=df_data['rarity'],
+                new_rarity=df_data['new_rarity_id'],
+                old_cost=df_data['cost']
+            )
+            params.extend([('cost', new_cost), ('rarity_id', df_data['new_rarity_id'])])
 
         if len(params) > 0:
             if df_data.player_id not in player_updates.keys():
diff --git a/creation_helpers.py b/creation_helpers.py
index 615f05f..9e93081 100644
--- a/creation_helpers.py
+++ b/creation_helpers.py
@@ -25,6 +25,54 @@ RARITY_BASE_COSTS = {
     99: 2400  # Special/Legend
 }
 
+# Rarity Cost Adjustments
+# Maps (old_rarity, new_rarity) -> (cost_adjustment, minimum_cost)
+# When a player's rarity changes, adjust their cost by the specified amount
+# and enforce minimum cost if specified (None = no minimum)
+RARITY_COST_ADJUSTMENTS = {
+    # From Diamond (1)
+    (1, 2): (-540, 100),
+    (1, 3): (-720, 50),
+    (1, 4): (-780, 15),
+    (1, 5): (-800, 5),
+    (1, 99): (1600, None),
+
+    # From Gold (2)
+    (2, 1): (540, None),
+    (2, 3): (-180, 50),
+    (2, 4): (-240, 15),
+    (2, 5): (-260, 5),
+    (2, 99): (2140, None),
+
+    # From Silver (3)
+    (3, 1): (720, None),
+    (3, 2): (180, None),
+    (3, 4): (-60, 15),
+    (3, 5): (-80, 5),
+    (3, 99): (2320, None),
+
+    # From Bronze (4)
+    (4, 1): (780, None),
+    (4, 2): (240, None),
+    (4, 3): (60, None),
+    (4, 5): (-20, 5),
+    (4, 99): (2380, None),
+
+    # From Common (5)
+    (5, 1): (800, None),
+    (5, 2): (260, None),
+    (5, 3): (80, None),
+    (5, 4): (20, None),
+    (5, 99): (2400, None),
+
+    # From Special/Legend (99)
+    (99, 1): (-1600, 800),
+    (99, 2): (-2140, 100),
+    (99, 3): (-2320, 50),
+    (99, 4): (-2380, 15),
+    (99, 5): (-2400, 5),
+}
+
 D20_CHANCES = {
         '2': {
             'chances': 1,
@@ -585,6 +633,61 @@ def should_update_player_description(
         return is_different and not is_potm
 
 
+def calculate_rarity_cost_adjustment(old_rarity: int, new_rarity: int, old_cost: int) -> int:
+    """
+    Calculate new cost when a player's rarity changes.
+
+    Uses the RARITY_COST_ADJUSTMENTS lookup table to determine the cost adjustment
+    and minimum cost when a player moves between rarity tiers.
+
+    Args:
+        old_rarity: Current rarity tier (1-5, 99)
+        new_rarity: New rarity tier (1-5, 99)
+        old_cost: Current player cost
+
+    Returns:
+        New cost after adjustment (with minimum enforced if applicable)
+
+    Examples:
+        >>> calculate_rarity_cost_adjustment(1, 2, 1000)
+        460  # Diamond to Gold: 1000 - 540 = 460, min 100 → 460
+
+        >>> calculate_rarity_cost_adjustment(1, 5, 100)
+        5  # Diamond to Common: 100 - 800 = -700, min 5 → 5
+
+        >>> calculate_rarity_cost_adjustment(5, 1, 50)
+        850  # Common to Diamond: 50 + 800 = 850, no min → 850
+
+        >>> calculate_rarity_cost_adjustment(3, 3, 100)
+        100  # No change: same rarity returns same cost
+    """
+    # No change if rarity stays the same
+    if old_rarity == new_rarity:
+        return old_cost
+
+    # Look up the adjustment and minimum cost
+    adjustment_data = RARITY_COST_ADJUSTMENTS.get((old_rarity, new_rarity))
+
+    if adjustment_data is None:
+        # No defined adjustment for this transition - return old cost
+        logger.warning(
+            f"creation_helpers.calculate_rarity_cost_adjustment - No cost adjustment defined for "
+            f"rarity change {old_rarity} → {new_rarity}. Keeping cost at {old_cost}."
+        )
+        return old_cost
+
+    cost_adjustment, min_cost = adjustment_data
+
+    # Calculate new cost
+    new_cost = old_cost + cost_adjustment
+
+    # Apply minimum cost if specified
+    if min_cost is not None:
+        new_cost = max(new_cost, min_cost)
+
+    return new_cost
+
+
 async def pd_players_df(cardset_id: int):
     p_query = await db_get(
         'players',
diff --git a/pitchers/creation.py b/pitchers/creation.py
index 4678ec2..84b89bf 100644
--- a/pitchers/creation.py
+++ b/pitchers/creation.py
@@ -5,7 +5,7 @@ import pandas as pd
 from creation_helpers import (
     get_all_pybaseball_ids, sanitize_name, CLUB_LIST, FRANCHISE_LIST, pd_players_df,
     mlbteam_and_franchise, NEW_PLAYER_COST, RARITY_BASE_COSTS,
-    should_update_player_description
+    should_update_player_description, calculate_rarity_cost_adjustment
 )
 from db_calls import db_post, db_get, db_put, db_patch
 from defenders import calcs_defense as cde
@@ -435,80 +435,13 @@ async def post_player_updates(
             ])
 
         elif df_data['rarity'] != df_data['new_rarity_id']:
-            old_rarity = df_data['rarity']
-            new_rarity = df_data['new_rarity_id']
-            old_cost = df_data['cost']
-            new_cost = 0
-
-            if old_rarity == 1:
-                if new_rarity == 2:
-                    new_cost = max(old_cost - 540, 100)
-                elif new_rarity == 3:
-                    new_cost = max(old_cost - 720, 50)
-                elif new_rarity == 4:
-                    new_cost = max(old_cost - 780, 15)
-                elif new_rarity == 5:
-                    new_cost = max(old_cost - 800, 5)
-                elif new_rarity == 99:
-                    new_cost = old_cost + 1600
-            elif old_rarity == 2:
-                if new_rarity == 1:
-                    new_cost = old_cost + 540
-                elif new_rarity == 3:
-                    new_cost = max(old_cost - 180, 50)
-                elif new_rarity == 4:
-                    new_cost = max(old_cost - 240, 15)
-                elif new_rarity == 5:
-                    new_cost = max(old_cost - 260, 5)
-                elif new_rarity == 99:
-                    new_cost = old_cost + 2140
-            elif old_rarity == 3:
-                if new_rarity == 1:
-                    new_cost = old_cost + 720
-                elif new_rarity == 2:
-                    new_cost = old_cost + 180
-                elif new_rarity == 4:
-                    new_cost = max(old_cost - 60, 15)
-                elif new_rarity == 5:
-                    new_cost = max(old_cost - 80, 5)
-                elif new_rarity == 99:
-                    new_cost = old_cost + 2320
-            elif old_rarity == 4:
-                if new_rarity == 1:
-                    new_cost = old_cost + 780
-                elif new_rarity == 2:
-                    new_cost = old_cost + 240
-                elif new_rarity == 3:
-                    new_cost = old_cost + 60
-                elif new_rarity == 5:
-                    new_cost = max(old_cost - 20, 5)
-                elif new_rarity == 99:
-                    new_cost = old_cost + 2380
-            elif old_rarity == 5:
-                if new_rarity == 1:
-                    new_cost = old_cost + 800
-                elif new_rarity == 2:
-                    new_cost = old_cost + 260
-                elif new_rarity == 3:
-                    new_cost = old_cost + 80
-                elif new_rarity == 4:
-                    new_cost = old_cost + 20
-                elif new_rarity == 99:
-                    new_cost = old_cost + 2400
-            elif old_rarity == 99:
-                if new_rarity == 1:
-                    new_cost = max(old_cost - 1600, 800)
-                elif new_rarity == 2:
-                    new_cost = max(old_cost - 2140, 100)
-                elif new_rarity == 3:
-                    new_cost = max(old_cost - 2320, 50)
-                elif new_rarity == 4:
-                    new_cost = max(old_cost - 2380, 15)
-                elif new_rarity == 5:
-                    new_cost = max(old_cost - 2400, 5)
-
-            if new_cost != 0:
-                params.extend([('cost', new_cost), ('rarity_id', new_rarity)])
+            # Calculate adjusted cost for rarity change using lookup table
+            new_cost = calculate_rarity_cost_adjustment(
+                old_rarity=df_data['rarity'],
+                new_rarity=df_data['new_rarity_id'],
+                old_cost=df_data['cost']
+            )
+            params.extend([('cost', new_cost), ('rarity_id', df_data['new_rarity_id'])])
 
         if len(params) > 0:
             if df_data.player_id not in player_updates.keys():
diff --git a/tests/test_rarity_cost_adjustments.py b/tests/test_rarity_cost_adjustments.py
new file mode 100644
index 0000000..fa4d51e
--- /dev/null
+++ b/tests/test_rarity_cost_adjustments.py
@@ -0,0 +1,184 @@
+"""
+Tests for rarity cost adjustment logic.
+
+This test verifies that calculate_rarity_cost_adjustment() correctly:
+1. Adjusts costs when rarity changes
+2. Enforces minimum costs where specified
+3. Handles all rarity transitions (1-5, 99)
+4. Returns original cost when rarity doesn't change
+"""
+import pytest
+from creation_helpers import calculate_rarity_cost_adjustment
+
+
+class TestRarityCostAdjustments:
+    """Test suite for rarity cost adjustment calculations."""
+
+    def test_no_change_same_rarity(self):
+        """Cost should not change if rarity stays the same."""
+        assert calculate_rarity_cost_adjustment(1, 1, 1000) == 1000
+        assert calculate_rarity_cost_adjustment(5, 5, 50) == 50
+        assert calculate_rarity_cost_adjustment(99, 99, 2400) == 2400
+
+    def test_diamond_to_gold(self):
+        """Diamond (1) to Gold (2): -540, min 100."""
+        assert calculate_rarity_cost_adjustment(1, 2, 1000) == 460
+        assert calculate_rarity_cost_adjustment(1, 2, 500) == 100  # min enforced
+        assert calculate_rarity_cost_adjustment(1, 2, 50) == 100  # min enforced
+
+    def test_diamond_to_silver(self):
+        """Diamond (1) to Silver (3): -720, min 50."""
+        assert calculate_rarity_cost_adjustment(1, 3, 1000) == 280
+        assert calculate_rarity_cost_adjustment(1, 3, 500) == 50  # min enforced
+        assert calculate_rarity_cost_adjustment(1, 3, 100) == 50  # min enforced
+
+    def test_diamond_to_bronze(self):
+        """Diamond (1) to Bronze (4): -780, min 15."""
+        assert calculate_rarity_cost_adjustment(1, 4, 1000) == 220
+        assert calculate_rarity_cost_adjustment(1, 4, 500) == 15  # min enforced
+        assert calculate_rarity_cost_adjustment(1, 4, 50) == 15  # min enforced
+
+    def test_diamond_to_common(self):
+        """Diamond (1) to Common (5): -800, min 5."""
+        assert calculate_rarity_cost_adjustment(1, 5, 1000) == 200
+        assert calculate_rarity_cost_adjustment(1, 5, 500) == 5  # min enforced
+        assert calculate_rarity_cost_adjustment(1, 5, 100) == 5  # min enforced
+
+    def test_diamond_to_special(self):
+        """Diamond (1) to Special (99): +1600, no min."""
+        assert calculate_rarity_cost_adjustment(1, 99, 1000) == 2600
+        assert calculate_rarity_cost_adjustment(1, 99, 100) == 1700
+
+    def test_gold_to_diamond(self):
+        """Gold (2) to Diamond (1): +540, no min."""
+        assert calculate_rarity_cost_adjustment(2, 1, 200) == 740
+        assert calculate_rarity_cost_adjustment(2, 1, 100) == 640
+
+    def test_gold_to_silver(self):
+        """Gold (2) to Silver (3): -180, min 50."""
+        assert calculate_rarity_cost_adjustment(2, 3, 300) == 120
+        assert calculate_rarity_cost_adjustment(2, 3, 100) == 50  # min enforced
+
+    def test_silver_to_gold(self):
+        """Silver (3) to Gold (2): +180, no min."""
+        assert calculate_rarity_cost_adjustment(3, 2, 100) == 280
+        assert calculate_rarity_cost_adjustment(3, 2, 50) == 230
+
+    def test_silver_to_bronze(self):
+        """Silver (3) to Bronze (4): -60, min 15."""
+        assert calculate_rarity_cost_adjustment(3, 4, 100) == 40
+        assert calculate_rarity_cost_adjustment(3, 4, 50) == 15  # min enforced
+
+    def test_bronze_to_common(self):
+        """Bronze (4) to Common (5): -20, min 5."""
+        assert calculate_rarity_cost_adjustment(4, 5, 50) == 30
+        assert calculate_rarity_cost_adjustment(4, 5, 20) == 5  # min enforced
+
+    def test_common_to_bronze(self):
+        """Common (5) to Bronze (4): +20, no min."""
+        assert calculate_rarity_cost_adjustment(5, 4, 10) == 30
+        assert calculate_rarity_cost_adjustment(5, 4, 50) == 70
+
+    def test_common_to_diamond(self):
+        """Common (5) to Diamond (1): +800, no min."""
+        assert calculate_rarity_cost_adjustment(5, 1, 10) == 810
+        assert calculate_rarity_cost_adjustment(5, 1, 50) == 850
+
+    def test_special_to_diamond(self):
+        """Special (99) to Diamond (1): -1600, min 800."""
+        assert calculate_rarity_cost_adjustment(99, 1, 2400) == 800
+        assert calculate_rarity_cost_adjustment(99, 1, 2000) == 800  # min enforced
+        assert calculate_rarity_cost_adjustment(99, 1, 3000) == 1400
+
+    def test_special_to_gold(self):
+        """Special (99) to Gold (2): -2140, min 100."""
+        assert calculate_rarity_cost_adjustment(99, 2, 2400) == 260
+        assert calculate_rarity_cost_adjustment(99, 2, 2000) == 100  # min enforced
+
+    def test_special_to_common(self):
+        """Special (99) to Common (5): -2400, min 5."""
+        assert calculate_rarity_cost_adjustment(99, 5, 2400) == 5  # min enforced
+        assert calculate_rarity_cost_adjustment(99, 5, 3000) == 600
+
+    def test_all_upward_transitions(self):
+        """Test all transitions that increase rarity (decrease number)."""
+        # Common (5) moving up
+        assert calculate_rarity_cost_adjustment(5, 4, 10) == 30   # +20
+        assert calculate_rarity_cost_adjustment(5, 3, 10) == 90   # +80
+        assert calculate_rarity_cost_adjustment(5, 2, 10) == 270  # +260
+        assert calculate_rarity_cost_adjustment(5, 1, 10) == 810  # +800
+
+        # Bronze (4) moving up
+        assert calculate_rarity_cost_adjustment(4, 3, 30) == 90   # +60
+        assert calculate_rarity_cost_adjustment(4, 2, 30) == 270  # +240
+        assert calculate_rarity_cost_adjustment(4, 1, 30) == 810  # +780
+
+        # Silver (3) moving up
+        assert calculate_rarity_cost_adjustment(3, 2, 90) == 270  # +180
+        assert calculate_rarity_cost_adjustment(3, 1, 90) == 810  # +720
+
+        # Gold (2) moving up
+        assert calculate_rarity_cost_adjustment(2, 1, 270) == 810  # +540
+
+    def test_all_downward_transitions_with_minimums(self):
+        """Test all transitions that decrease rarity (increase number) with minimum enforcement."""
+        # Diamond (1) moving down - all have minimums
+        assert calculate_rarity_cost_adjustment(1, 2, 100) == 100  # would be -440, min 100
+        assert calculate_rarity_cost_adjustment(1, 3, 100) == 50   # would be -620, min 50
+        assert calculate_rarity_cost_adjustment(1, 4, 100) == 15   # would be -680, min 15
+        assert calculate_rarity_cost_adjustment(1, 5, 100) == 5    # would be -700, min 5
+
+        # Gold (2) moving down - all have minimums
+        assert calculate_rarity_cost_adjustment(2, 3, 100) == 50   # would be -80, min 50
+        assert calculate_rarity_cost_adjustment(2, 4, 100) == 15   # would be -140, min 15
+        assert calculate_rarity_cost_adjustment(2, 5, 100) == 5    # would be -160, min 5
+
+        # Silver (3) moving down - all have minimums
+        assert calculate_rarity_cost_adjustment(3, 4, 50) == 15    # would be -10, min 15
+        assert calculate_rarity_cost_adjustment(3, 5, 50) == 5     # would be -30, min 5
+
+    def test_edge_cases(self):
+        """Test edge cases: zero cost, very high cost, etc."""
+        # Zero cost
+        assert calculate_rarity_cost_adjustment(5, 1, 0) == 800
+        assert calculate_rarity_cost_adjustment(1, 5, 0) == 5  # min enforced
+
+        # Very high cost
+        assert calculate_rarity_cost_adjustment(5, 1, 10000) == 10800
+        assert calculate_rarity_cost_adjustment(99, 1, 10000) == 8400
+
+    def test_symmetry(self):
+        """Test that adjustments are symmetric (up then down returns close to original)."""
+        # Diamond to Common and back (won't be exact due to minimums, but should be logical)
+        original = 810
+        after_down = calculate_rarity_cost_adjustment(1, 5, original)  # 810 - 800 = 10, min 5 → 5
+        after_up = calculate_rarity_cost_adjustment(5, 1, after_down)  # 5 + 800 = 805
+        assert after_down == 10
+        assert after_up == 810
+
+        # Gold to Bronze and back
+        original = 270
+        after_down = calculate_rarity_cost_adjustment(2, 4, original)  # 270 - 240 = 30
+        after_up = calculate_rarity_cost_adjustment(4, 2, after_down)  # 30 + 240 = 270
+        assert after_down == 30
+        assert after_up == 270
+
+
+class TestRarityCostAdjustmentEdgeCases:
+    """Test edge cases and error handling."""
+
+    def test_undefined_transition(self):
+        """Test that undefined transitions are handled gracefully."""
+        # There's no transition from 1 to 1 (same), but it's handled
+        result = calculate_rarity_cost_adjustment(1, 1, 500)
+        assert result == 500
+
+        # There's no transition from rarity 10 (doesn't exist) but should return old cost
+        result = calculate_rarity_cost_adjustment(10, 5, 500)
+        assert result == 500  # Falls back to old cost
+
+    def test_negative_costs(self):
+        """Test behavior with negative costs (shouldn't happen, but test it)."""
+        # Negative costs should still get adjusted
+        result = calculate_rarity_cost_adjustment(5, 1, -100)
+        assert result == 700  # -100 + 800 = 700