Baby Weight Gain Since Birth Calculator

In the first 4 weeks, the American Academy of Pediatrics considers 20–35 g/day (0.7–1.2 oz/day) normal. From 1–3 months, expect 20–30 g/day. Gain slows to 10–20 g/day at 3–6 months, then 5–15 g/day from 6–12 months. After age 1, typical gain is just 2–8 g/day.

Most healthy newborns lose 5–10% of birth weight in the first few days. The AAP expects babies to return to birth weight by day 10–14. Breastfed babies may take a day or two longer than formula-fed. If your baby hasn't regained birth weight by 2 weeks, contact your pediatrician.

Rapid weight gain in infancy is generally not a concern and does not predict obesity later in life for breastfed babies. For formula-fed babies, very rapid gain may prompt a conversation about feeding volumes. Discuss patterns with your pediatrician rather than trying to adjust feeds on your own.

Poor weight gain (failure to thrive) can have many causes including inadequate milk supply, latching difficulty, formula preparation errors, or underlying medical conditions. Contact your pediatrician or a lactation consultant — weight trends of 2+ weeks give more insight than a single measurement.

Total weight gained (current weight minus birth weight) is divided by the number of days since birth to get grams per day. This calculator also shows ounces per week for parents who prefer imperial units. Both metrics help you compare against AAP age-specific ranges.