diff --git a/accountant/api/models/operations.py b/accountant/api/models/operations.py
index b6ae971..15db841 100644
--- a/accountant/api/models/operations.py
+++ b/accountant/api/models/operations.py
@@ -158,15 +158,18 @@ class Operation(db.Model):
             db.func.sum(cls.value).label("balance")
         ).filter(
             cls.account_id == account_id
-        ).filter(
-            cls.operation_date >= str(begin),
-            cls.operation_date <= str(end)
         ).order_by(
             cls.category
         ).group_by(
             cls.category
         )
 
+        if begin:
+            query = query.filter(cls.operation_date >= str(begin))
+
+        if end:
+            query = query.filter(cls.operation_date <= str(end))
+
         return query
 
     @classmethod