Question: how many calories does a baby need to gain weight?
Answer: Once you know that, you can calculate the average amount of calories needed to grow this way: Age newborn to 3 months: 100 calories per kilogram per day. Age 3 months to 3 years : 90-100 calories per kilogram per day. Age 3 years to 8 years: 80-90 calories per kilogram per day.