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diff --git a/src/plant_transaction_data/__pycache__/service.cpython-311.pyc b/src/plant_transaction_data/__pycache__/service.cpython-311.pyc
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diff --git a/src/plant_transaction_data/router.py b/src/plant_transaction_data/router.py
index dd85df6..be7c870 100644
--- a/src/plant_transaction_data/router.py
+++ b/src/plant_transaction_data/router.py
@@ -40,16 +40,15 @@ async def get_transaction_datas(
         message="Data retrieved successfully",
     )
 
-
 @router.get("/charts", response_model=StandardResponse[PlantChartData])
 async def get_chart_data(db_session: DbSession, common: CommonParameters):
     chart_data, bep_year, bep_total_lcc = await get_charts(
         db_session=db_session, common=common
     )
-    if not chart_data or not bep_year:
+    if not chart_data:
         raise HTTPException(
             status_code=status.HTTP_404_NOT_FOUND,
-            detail="A data with this id does not exist.",
+            detail="No chart data found.",
         )
     return StandardResponse(
         data={
@@ -60,7 +59,6 @@ async def get_chart_data(db_session: DbSession, common: CommonParameters):
         message="Data retrieved successfully",
     )
 
-
 @router.get(
     "/{transaction_data_id}", response_model=StandardResponse[PlantTransactionDataRead]
 )
diff --git a/src/plant_transaction_data/service.py b/src/plant_transaction_data/service.py
index c5cded4..26dc898 100644
--- a/src/plant_transaction_data/service.py
+++ b/src/plant_transaction_data/service.py
@@ -60,9 +60,9 @@ async def get_charts(
 
     chart_data = results.scalars().all()
     bep_year = None
-    previous_year = 0
-    previous_total_cost = 0
-    previous_revenue = 0
+    previous_year = None
+    previous_total_cost = None
+    previous_revenue = None
     bep_total_lcc = 0
 
     for idx, item in enumerate(chart_data):
@@ -73,16 +73,36 @@ async def get_charts(
         )
         revenue = item.chart_revenue_annualized
 
-        if previous_total_cost and previous_revenue:
-            if (previous_total_cost > previous_revenue and total_cost < revenue) or (
-                previous_total_cost < previous_revenue and total_cost > revenue
-            ):
-                if total_cost < revenue:
-                    bep_total_lcc = previous_total_cost
-                    bep_year = previous_year
+        if previous_total_cost is not None and previous_revenue is not None:
+            prev_diff = previous_total_cost - previous_revenue
+            curr_diff = total_cost - revenue
+
+            # If signs differ there's a crossing between previous and current point
+            if prev_diff == 0:
+                bep_year = previous_year
+                bep_total_lcc = previous_total_cost
+                break
+
+            if prev_diff * curr_diff < 0:
+                # Interpolate linearly between the two years to estimate BEP year
+                denom = ( (total_cost - previous_total_cost) - (revenue - previous_revenue) )
+                if denom != 0:
+                    t = (previous_revenue - previous_total_cost) / denom
+                    # clamp t to [0,1]
+                    t = max(0.0, min(1.0, t))
+                    try:
+                        bep_year = previous_year + t * (item.tahun - previous_year)
+                    except Exception:
+                        bep_year = previous_year
+                    bep_total_lcc = previous_total_cost + t * (total_cost - previous_total_cost)
                 else:
-                    bep_total_lcc = total_cost
-                    bep_year = item.tahun
+                    # fallback if interpolation is not possible
+                    if total_cost < revenue:
+                        bep_total_lcc = previous_total_cost
+                        bep_year = previous_year
+                    else:
+                        bep_total_lcc = total_cost
+                        bep_year = item.tahun
                 break
 
         previous_total_cost = total_cost