Answer:
200 additional calories per day
Explanation
Kellymom.com is a great place for breastfeeding information. There is much more then that as well.
https://kellymom.com/nutrition/mothers-diet/mom-calories-fluids/
An exclusively breastfeeding mother, on average, needs to take in 300-500 calories per day above what was needed to maintain pre-pregnancy weight. Since the recommended added calories during the last two trimesters of pregnancy is 300 calories/day, an exclusively breastfeeding mother will typically need either the same amount of calories she was getting at the end of pregnancy, or up to 200 additional calories per day. That’s the equivalent of adding 1-2 healthy snacks per day.
Per Breastfeeding and Human Lactation (Riordan, 2004, p. 438), “The amount of energy needed by lactating mothers continues to be debated. The lactating mother need not maintain a markedly higher caloric intake than that maintained prior to pregnancy: in most cases, 400-500 calories in excess of that which is needed to maintain the mother’s body weight is sufficient.”
