Baby Weight Gain by Month: How Much Should My Baby Weigh?
Month-by-month average weight gain for babies 0–12 months, WHO growth chart reference, and what to do if your baby is gaining slowly.
Every pediatric visit comes with a weigh-in that feels high-stakes. But here's the most important thing to know: there's no single "correct" weight for your baby's age. What matters is that they're tracking along their own growth curve consistently over time.
Average Weight Gain by Age (WHO Reference)
- 0–3 months: ~150–200g/week (about 20–30g/day)
- 3–6 months: ~100–150g/week
- 6–9 months: ~70–100g/week
- 9–12 months: ~50–70g/week
Average Weight at Each Month (Reference Only)
- Birth: 3.3 kg / 7.3 lbs (average)
- 3 months: 6.0 kg / 13.2 lbs (boys); 5.5 kg / 12.1 lbs (girls)
- 6 months: 7.9 kg / 17.4 lbs (boys); 7.3 kg / 16.1 lbs (girls)
- 9 months: 9.2 kg / 20.3 lbs (boys); 8.6 kg / 19.0 lbs (girls)
- 12 months: 10.2 kg / 22.5 lbs (boys); 9.5 kg / 20.9 lbs (girls)
💡 Log every pediatric visit in BabySync — height, weight, and head circumference. Over time you'll build a complete growth history that you can ask ChatGPT to analyze: "Is my baby's growth rate consistent with their curve?" or "Have there been any unexpected drops?" Data-backed conversations with your pediatrician start here.
If Your Baby Is Gaining Slowly: Possible Causes
- Insufficient milk intake — consider increasing feed frequency or offering formula top-ups
- Latch issues — consult a certified lactation consultant (IBCLC)
- Frequent vomiting or reflux — ask your pediatrician about GERD
- Dairy allergy or lactose intolerance — requires testing
- Underlying medical condition — requires pediatric evaluation
Understanding Growth Percentiles
The WHO and CDC growth charts plot your baby's measurements against all babies of the same age and sex. Any percentile between 3 and 97 is considered normal. A baby at the 10th percentile is not "too small" — they may simply be built small. What concerns pediatricians is a baby who crosses two major percentile lines downward or who actually loses weight.
⚠️ If your baby drops across two major percentile lines (e.g., 75th to 25th) or actually loses weight after the first 2 weeks, contact your pediatrician promptly.