diff --git a/uncloud/uncloud_pay/models.py b/uncloud/uncloud_pay/models.py
index 643361a..c824a00 100644
--- a/uncloud/uncloud_pay/models.py
+++ b/uncloud/uncloud_pay/models.py
@@ -9,8 +9,7 @@ AMOUNT_DECIMALS=2
 
 class Bill(models.Model):
     owner = models.ForeignKey(get_user_model(),
-            on_delete=models.CASCADE,
-            editable=False)
+            on_delete=models.CASCADE)
 
     creation_date = models.DateTimeField()
     starting_date = models.DateTimeField()
@@ -23,7 +22,7 @@ class Bill(models.Model):
     @property
     def amount(self):
         # iterate over all related orders
-        pass
+        return 20
 
 
 class Order(models.Model):
@@ -82,6 +81,9 @@ class PaymentMethod(models.Model):
     description = models.TextField()
     primary = models.BooleanField(default=True)
 
+    def charge(self, amount):
+        pass
+
     class Meta:
         unique_together = [['owner', 'primary']]
 
@@ -89,8 +91,7 @@ class Payment(models.Model):
     uuid = models.UUIDField(primary_key=True, default=uuid.uuid4, editable=False)
 
     owner = models.ForeignKey(get_user_model(),
-            on_delete=models.CASCADE,
-            editable=False)
+            on_delete=models.CASCADE)
 
     amount = models.DecimalField(
             default=0.0,
diff --git a/uncloud/uncloud_pay/serializers.py b/uncloud/uncloud_pay/serializers.py
index 93a3031..040c78a 100644
--- a/uncloud/uncloud_pay/serializers.py
+++ b/uncloud/uncloud_pay/serializers.py
@@ -2,6 +2,8 @@ from django.contrib.auth import get_user_model
 from rest_framework import serializers
 from .models import *
 
+from functools import reduce
+
 class BillSerializer(serializers.ModelSerializer):
     class Meta:
         model = Bill
@@ -26,7 +28,16 @@ class OrderSerializer(serializers.ModelSerializer):
 class UserSerializer(serializers.ModelSerializer):
     class Meta:
         model = get_user_model()
-        fields = ['username', 'email']
+        fields = ['username', 'email', 'balance']
 
-    def get_balance(self, obj):
-        return 666
+    # Display current 'balance'
+    balance = serializers.SerializerMethodField('get_balance')
+    def __sum_balance(self, entries):
+        return reduce(lambda acc, entry: acc + entry.amount, entries, 0)
+
+    def get_balance(self, user):
+        bills = self.__sum_balance(Bill.objects.filter(owner=user))
+        payments = self.__sum_balance(Payment.objects.filter(owner=user))
+        balance = payments - bills
+
+        return balance
diff --git a/uncloud/uncloud_pay/views.py b/uncloud/uncloud_pay/views.py
index 0b39ff3..ea3cca7 100644
--- a/uncloud/uncloud_pay/views.py
+++ b/uncloud/uncloud_pay/views.py
@@ -4,6 +4,8 @@ from rest_framework import viewsets, permissions, status
 from rest_framework.response import Response
 from rest_framework.decorators import action
 
+import json
+
 from .models import *
 from .serializers import *
 from datetime import datetime
@@ -54,10 +56,6 @@ class UserViewSet(viewsets.ReadOnlyModelViewSet):
     def get_queryset(self):
         return get_user_model().objects.all()
 
-    @action(detail=True)
-    def balance(self, request):
-        return Response(status=status.HTTP_204_NO_CONTENT)
-
 class PaymentMethodViewSet(viewsets.ModelViewSet):
     serializer_class = PaymentMethodSerializer
     permission_classes = [permissions.IsAuthenticated]
@@ -104,7 +102,7 @@ class AdminBillViewSet(viewsets.ModelViewSet):
     def create(self, request):
         serializer = self.get_serializer(data=request.data)
         serializer.is_valid(raise_exception=True)
-        serializer.save(created_at=datetime.now())
+        serializer.save(creation_date=datetime.now())
 
         headers = self.get_success_headers(serializer.data)
         return Response(serializer.data, status=status.HTTP_201_CREATED, headers=headers)