Baby Growth Reference Calculator
Compare an infant’s weight and length with WHO median reference values for age and sex, from birth to 24 months.
Formula and sources updated · Data sources · 2View algorithm, constants and default inputs (JSON)
Results
About this calculator
This page shows the WHO 50th-percentile reference for weight-for-age and length-for-age, with linear interpolation between whole months. It does not calculate a percentile or assess growth over time. Use accurate measurements and ask a child’s clinician to interpret the pattern; growth charts are not a diagnosis on their own.
Worked example
calculated with the default values below
Age 6 months · Sex used by the reference chart Boy · Current weight 8.2 kg · Current recumbent length 68 cm WHO median weight for age 7.90 kg · WHO median length for age 67.6 cm · Weight difference from median 0.30 kg · Length difference from median 0.4 cm
Data sources
Disclaimer
These calculators are for general information only and are not a medical device, a diagnosis or a treatment plan. Reference ranges describe populations, not individuals, and do not account for pregnancy, medication, disability or athletic training. Discuss your own situation with a qualified healthcare professional.
Implementation source
This record describes the implementation used by this page. It is not independent validation. External references, when available, support only the stated formula or definition; estimates and custom rules retain their own assumptions.
Formula and variables
M(a) = T⌊a⌋ + (T⌊a⌋₊₁ − T⌊a⌋) × frac(a)
- Tᵢ
- WHO 50th-percentile reference at whole month i
- a
- Age in months, limited to 0–24
- frac(a)
- Fractional part of age in months
- M(a)
- Interpolated median reference value
Tᵢ is the WHO 50th-percentile reference value for the selected sex at whole-month age i. Values between months are linearly interpolated. This page shows a reference median; it does not calculate a child’s percentile, z-score, weight-for-length, prematurity correction, or growth trend.
Frequently asked questions
Does this calculate my baby’s percentile?
No. The table contains the WHO 50th-percentile (median) values for weight-for-age and length-for-age from birth to 24 months; half-month ages are linearly interpolated. The page does not calculate an individual percentile or z-score, compare weight with length, account for prematurity, or evaluate a series of measurements. CDC says growth charts contribute to an overall assessment and are not a stand-alone diagnostic tool. Ask your child’s clinician to interpret accurate measurements over time.