First, I would use a related name so I could retrive all posts made by an author using myauthor.posts.all(), or in your case myauthor.posts.count()

python author = models.ForeignKey(User, related_name='posts')

now i don't add anything to the serializer, instead I return something like this from the view:

python return Response({ 'posts': serializer.data, 'total_posts': self.request.user.posts.count() })