diff --git a/work_helpers/travels.py b/work_helpers/travels.py
index 187afed..9e20106 100644
--- a/work_helpers/travels.py
+++ b/work_helpers/travels.py
@@ -191,11 +191,18 @@ def _read_pre_payments(file_path: Pathlike = None) -> PrePayments:
     mask = raw_data["Werttyp"].isin(("Rechnung", "Umbuchung", "Zahlung"))
     raw_payments = raw_data[mask].copy()
 
-    summary = (
+    aggregate = (
         raw_payments.groupby("BelegNr")
         .agg({"Betrag": "sum", "BuDat": "first"})
         .reset_index()
-        .sort_values("BelegNr")
+        
+    )
+    
+    aggregate["sorting"] = pd.to_datetime(aggregate["BuDat"]).dt.date
+    summary = (
+        aggregate
+        .sort_values("sorting")
+        .drop(columns=["sorting"])
     )
 
     paymments = [