diff --git a/accountant/api/models/entries.py b/accountant/api/models/entries.py
index cd8e052..bb71687 100644
--- a/accountant/api/models/entries.py
+++ b/accountant/api/models/entries.py
@@ -15,7 +15,8 @@
     along with Accountant.  If not, see <http://www.gnu.org/licenses/>.
 """
 
-from sqlalchemy import distinct, func, cast, extract
+from sqlalchemy import distinct, func, case, cast, extract
+
 from accountant import db
 
 
diff --git a/accountant/api/models/operations.py b/accountant/api/models/operations.py
index d0dda60..d1d3c58 100644
--- a/accountant/api/models/operations.py
+++ b/accountant/api/models/operations.py
@@ -107,3 +107,32 @@ class Operation(db.Model):
     @classmethod
     def get(cls, session, id):
         return session.query(cls).filter(cls.id == id).one()
+
+    @classmethod
+    def get_categories_for_range(cls, session, account, begin, end):
+        if isinstance(account, int) or isinstance(account, str):
+            account_id = account
+        else:
+            account_id = account.id
+
+        query = session.query(
+            cls.category,
+            func.sum(
+                case([(func.sign(cls.value) == -1, cls.value)], else_=0)
+            ).label("expenses"),
+            func.sum(
+                case([(func.sign(cls.value) == 1, cls.value)], else_=0)
+            ).label("revenues"),
+            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
+        )
+
+        return query