Baby Percentile Calculator
Calculate weight and length percentiles for babies aged 0–24 months using WHO/CDC-derived reference values.
What is Baby Percentile?
Baby percentile charts compare your child's measurements to a large reference population of the same age and sex. A percentile of 50 means a baby is right in the middle; 90 means heavier or longer than 90% of peers; 10 means lighter or shorter than 90% of peers. Healthy babies grow along their own curve — what matters most is the trend, not a single point.
Pediatricians use the WHO standards for ages 0–2 (which describe optimal growth of breastfed babies under ideal conditions) and the CDC charts thereafter. This calculator uses simplified mean-and-SD approximations of those datasets and is intended for everyday parental insight rather than clinical diagnosis.
How is it calculated?
The percentile is computed from a z-score: z = (your value − reference mean) / reference SD. The z-score is converted to a percentile via the standard normal cumulative distribution. Reference values used are age- and sex-specific approximations of the published WHO/CDC LMS tables.
Frequently Asked Questions
- Should I worry about a low percentile?
- Steady growth along any percentile is usually fine; sudden drops warrant a paediatric review.
- Why does my baby's percentile differ from clinic?
- Clinic charts use full LMS curves; this calculator uses approximations. Always trust the clinic chart.
- Are formula-fed and breastfed babies on the same chart?
- WHO charts (used here for under-2) are based on breastfed infants; CDC charts apply mixed feeding.
- How often should percentiles be checked?
- At every well-baby visit (about every 2–3 months in the first year).