GROWTH PERCENTILE
What percentile is my baby?
Enter your baby's sex, age, weight and length. The calculator applies the WHO Child Growth Standards and shows the percentile behind every number.
Last reviewed:
Guidance only: A percentile is not a grade and not a diagnosis. Most healthy babies fall between the 3rd and 97th percentiles, and crossing lines matters more than any single point. If growth is below the 3rd, above the 97th, or drops across lines, talk to your pediatrician.
Your result
For a boy, 6 months old, 7.9 kg, 67.6 cm
- Weight-for-age
- p48.4
- Between the 3rd and 97th percentiles — the typical range.
- Length-for-age
- p49.6
- Between the 3rd and 97th percentiles — the typical range.
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WHO medians (50th percentile) by age
| Age | Boys weight | Girls weight | Boys length | Girls length |
|---|---|---|---|---|
| 0 mo | 3.3464 kg | 3.2322 kg | 49.8842 cm | 49.1477 cm |
| 6 mo | 7.934 kg | 7.297 kg | 67.6236 cm | 65.7311 cm |
| 12 mo | 9.6479 kg | 8.9481 kg | 75.7488 cm | 74.015 cm |
| 18 mo | 10.9385 kg | 10.2315 kg | 82.2587 cm | 80.7079 cm |
| 24 mo | 12.1515 kg | 11.4775 kg | 87.8161 cm | 86.4153 cm |
How this is calculated
The tool takes completed months (floor of the age you enter), looks up the WHO [L, M, S] values for that month and sex, computes z = ((x/M)^L − 1) / (L·S), and converts z to a percentile with the standard normal curve. Displayed percentiles clamp to 0.1–99.9; nothing is extrapolated past 24 months.
The LMS method. WHO standards are skew-corrected: L adjusts for skew, M is the median, S is variation. A z of 0 is exactly the median (50th percentile); ±2 is roughly the 2nd and 98th.
One point is not a curve. Pediatricians read the line across visits, not one dot. Log weight and length in the app after each checkup and the curve draws itself.
When to ask your pediatrician. Below the 3rd or above the 97th percentile, a drop across two percentile lines, or weight and length telling very different stories — bring the log and ask.
Questions
- What percentile should my baby be in?
- There is no target percentile. By definition half of healthy babies are below the 50th and half above. The typical range spans the 3rd to the 97th; where a baby sits inside it matters less than staying roughly on their curve.
- My baby dropped from the 60th to the 40th percentile. Is that bad?
- A single move inside the typical range is usually normal variation or measurement noise. Pediatricians watch for drops across two or more percentile lines, or a steady downward trend across visits — bring the history and ask.
- Are boys and girls measured on different charts?
- Yes. WHO publishes separate boys and girls tables for every indicator, because growth patterns differ by sex from birth. This calculator switches tables automatically when you pick a sex.
- Why completed months and not exact age?
- WHO standards are tabulated by completed month (a 4-month-and-3-week-old counts as 4 months). That is the convention clinics use, so the calculator follows it for comparable numbers.
- Do I need the weight-for-length chart too?
- Weight-for-length answers a different question (proportionality) and needs same-day weight and length. This tool covers weight-for-age and length-for-age, the two age-tracking charts; ask your pediatrician about proportionality at checkups.
- Is BMI a thing for babies?
- No. BMI-for-age starts at 2 years in the WHO standards. Under 2, clinicians use weight-for-age, length-for-age, and weight-for-length — never BMI.
- How often should I measure?
- At each well-child visit is enough; weekly home weigh-ins mostly capture scale and time-of-day noise. If you track at home, same scale, same time of day, and look at the trend.
Track it in the app, not on a calculator
This is a planning range. The number that matters is what your baby actually takes. Log a feed in one tap and see today's total without adding anything up.
- ✓One tap to log a feed
- ✓Today's total, automatic
- ✓Share with the other caregiver
Sources
- [1]WHO Multicentre Growth Reference Study, "Weight-for-age: Birth to 5 years (z-scores)," reviewed 2006. who.int ↗
- [2]WHO Multicentre Growth Reference Study, "Length-for-age: Birth to 2 years (z-scores)," reviewed 2006. who.int ↗
Accessed: 2026-10-15.
A planning estimate, not medical advice
This tool applies published guidance to the numbers you enter. Every baby is different. Use the result as a starting point and follow your pediatrician's advice for your baby.