Parents may report lower happiness due to less income for self-focused activities, less sleep, and less time for exercise.

“We could imagine, for instance, that people who opt not to have children have more income to devote to things more focused on themselves or their partner or other aspects of their life. We don't know if that's the underlying reason. We could perhaps conclude that people who opt not to have children are getting more sleep on a regular basis or have more time for exercise or the other sorts of things that elevate states of mood and well-being. Again we do not know what the underlying reasons are for this finding.”