The standard figure cited for breastfeeding is that it uses an extra 500 calories per day; an incentive to loose the pregnancy weight.
The English National Health Service (their agent of evil socialism), reports something even better. Sex will use up 300 calories per hour. Giving you a whole-body cardiovascular work-out and reducing the risk of heart disease. I suppose this figure depends upon how ... enthusiastic ... you are.
And, yet again even better:
If you're worried about wrinkles - orgasms even help prevent frown lines from deepening
22 hours ago