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Free baby weight percentile estimator for infants 0–24 months: compare weight to smoothed P3–P50–P97 bands by sex and age. Pair planning with our pregnancy weight gain calculator for the prenatal chapter—then bring printed curves to your pediatric visits.
Last updated: April 18, 2026
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Use completed months plus fraction if needed (0–24).
Estimated percentile
50%
z-score ≈ 0
P3
6.4 kg
P50
7.9 kg
P97
9.5 kg
Weight used: 7.9 kg at 6 mo
Not medical advice. Any feeding concern, poor gain, or illness needs your pediatric clinician—not an online chart.
Scope
0–24 months
Matches the window parents most often discuss with routine infant visits.
Charts differ
Separate references
Median and spread shift by sex—pick the right option before reading the percentile.
Not only one number
See the rails
The tool surfaces common outer and middle bands to interpret where weight sits—not just a percentile.
Conversion
Internal kg math
Pick the unit your scale shows; we convert to kilograms for the chart math.
Growth velocity
Plot over visits
A single percentile cannot replace serial measurements on your doctor’s chart.
Special cases
Ask your team
Premature infants and complex conditions need individualized growth plans.
Male, 6 months, 7.9 kg → about 50% in this model (near the median band for that age).
We interpolate smoothed P3, P50, and P97 weight points by age in months, then estimate a z-score assuming a normal distribution whose spread is consistent with the distance between those outer percentiles. The reported percentile is the corresponding area under that bell curve. This mirrors common spreadsheet approaches used for quick screening—not the full LMS pipeline used in official software. Browse more fitness & lifestyle calculators for maternal and family planning tools.
Interpolated P3, P50, P97 at the baby's age (months)
σ ≈ (P97 − P3) / 3.76
z = (weight_kg − P50) / σ
percentile ≈ Φ(z) × 100
Φ is the standard normal CDF. Extreme weights can land outside typical chart ranges—your pediatrician interprets those cases in context.
Tracking your own postpartum weight? Try the postpartum weight loss calculator.
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