Baby weight percentile calculator
Enter your baby's weight in kg or lb and oz with their date of birth. You'll get the weight-for-age percentile and the median weight for their age.
WHO is what US paediatricians use under 2. For premature babies, percentiles use corrected age until 2 years.
Enter weight to see the percentile and where it sits on the WHO curves.
What a percentile actually means
Imagine 100 healthy, breastfed six-month-old girls from the WHO study, lined up from lightest to heaviest. A baby "on the 30th percentile" is heavier than about 30 of them and lighter than about 70. Drag to pick a baby.
- The 50th isn't the "goal". The 10th and the 90th percentile are both perfectly healthy positions. Half of all healthy babies are below the median.
- Percentiles squash at the edges. Moving from the 50th to the 84th takes one standard deviation (0.95 kg here); moving from the 97th to the 99th takes much less than that. So a jump between high percentiles can mean a few grams.
- The curve matters more than the dot. Paediatricians watch whether a baby follows roughly the same line over time. Crossing two major centile lines downwards is what prompts a closer look.
Average baby weight by month (WHO median)
| Age | Boys | Girls |
|---|---|---|
| Birth | 3.3 kg | 3.2 kg |
| 1 mo | 4.5 kg | 4.2 kg |
| 2 mo | 5.6 kg | 5.1 kg |
| 3 mo | 6.4 kg | 5.8 kg |
| 4 mo | 7.0 kg | 6.4 kg |
| 6 mo | 7.9 kg | 7.3 kg |
| 9 mo | 8.9 kg | 8.2 kg |
| 12 mo | 9.6 kg | 8.9 kg |
| 18 mo | 10.9 kg | 10.2 kg |
| 2 yrs | 12.2 kg | 11.5 kg |
Frequently asked questions
How much weight should a baby gain per week?
Roughly 150–200 g (5–7 oz) a week in the first 3 months, 100–150 g a week from 3 to 6 months, and 70–90 g a week from 6 to 12 months. Most babies double their birth weight by about 4–5 months and triple it by their first birthday.
Is it normal for babies to lose weight after birth?
Yes. Newborns commonly lose up to 7–10% of their birth weight in the first few days and usually regain it by 10–14 days. The WHO chart starts at birth, so percentiles in the first two weeks often look low while babies catch up.
Is the 5th percentile for weight too small?
Not by itself. The 5th percentile is within the normal range. What matters is whether your baby keeps growing along a similar line and is feeding, weeing and developing well.
Data: WHO Child Growth Standards (2006) LMS tables, birth to 5 years; CDC 2000 growth charts LMS tables (cdc.gov/growthcharts), birth to 20 years. Percentiles are computed with the LMS method: z = ((X/M)^L − 1) / (L·S). The CDC recommends the WHO standards for all US children under 2.