Have you tried my Healthy Kid Calculator®? If you would send your son’s length and weight and approximate wake and sleep hours, I will provide you the calorie amount for a 5-month-old. However, this amount will increase each month as he gets older. So this calorie amount would only be a snapshot for a 5-month-old. It would not be enough for a 6-month-old.
The focus is not just calories for infants, but rather to provide adequate food (breast milk or formula) to support increases in length and weight and head circumference which show growth. Generally, babies will eat until they are full and stop. So I would recommend feeding your 5-month-old at least 3 meals and 3 – 4 bottles (8 ounces each bottle) during the day. Babies only need 1 or 2 Tbsp of food at a meal though.
Generally speaking breast milk or formula is sufficient for the first 4 – 6 months of life. Usually, 1 quart of milk or formula per day is adequate, but this does vary from infant to infant. Solids like pablum and fruit are started around 4 – 6 months of age, vegetables around 6 – 7 months and egg yolks or meat around 8 – 9 months. Recent recommendations from the American Academy of Pediatrics has delayed the introduction of solid food to about 6 months of age, but this guideline is for an average infant and should not be generalized for every infant. Some low birth weight infants need more food sooner to catch up their weight.
If this is your first child, perhaps it would be helpful to talk to a Registered Dietitian about what to feed your baby for optimal brain and physical development. Babies are tough to figure out because they don’t come with a manual or instruction booklet and each baby is different with regards to their nutrition needs.