diff --git a/src/calculation_time_constrains/service.py b/src/calculation_time_constrains/service.py
index 3c17bba..5859ce7 100644
--- a/src/calculation_time_constrains/service.py
+++ b/src/calculation_time_constrains/service.py
@@ -25,7 +25,7 @@ from .schema import (CalculationResultsRead,
 
 from .utils import get_months_between
 from src.scope_equipment_part.model import ScopeEquipmentPart
-
+import copy
 
 class ReliabilityService:
     """Service class for handling reliability API calls"""
@@ -500,7 +500,7 @@ async def run_simulation(*, db_session: DbSession, calculation: CalculationData,
     spareparts = {
         sparepart.id: {
             'data': sparepart,
-            'stock': sparepart.stock
+            'stock': copy.copy(sparepart.stock)
         } for sparepart in sparepars_query.scalars().all()
     }