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Free baby weight percentile calculator for infants 0–24 months. Enter sex, age, and weight (kg or lb) to estimate weight-for-age percentile, z-score, and P3 / P50 / P97 reference weights. Educational — not a replacement for your pediatric growth chart.
Last updated: May 24, 2026
Prenatal planning? Pregnancy weight gain calculator
Use completed months plus fraction if needed (0–24).
Estimated percentile
50%
Middle range
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.
Estimated percentile from weight vs interpolated P3–P50–P97 at your baby's age.
50%
Middle range
P3: 6.4 kg
P50: 7.9 kg
P97: 9.5 kg
0
0 = median; negative = below median in this model
Percentile
50%
Median (P50)
7.9 kg
z-score
0
Band
Middle range
| Age (mo) | P3 | P50 (median) | P97 |
|---|---|---|---|
| 0 | 2.50 | 3.30 | 4.40 |
| 3 | 5.00 | 6.40 | 7.70 |
| 6 | 6.40 | 7.90 | 9.50 |
| 12 | 7.80 | 9.60 | 11.30 |
| 18 | 8.90 | 10.90 | 12.90 |
| 24 | 9.90 | 12.20 | 14.30 |
| Age (mo) | P3 | P50 (median) | P97 |
|---|---|---|---|
| 0 | 2.40 | 3.20 | 4.20 |
| 3 | 4.50 | 5.80 | 7.40 |
| 6 | 5.70 | 7.30 | 9.20 |
| 12 | 7.00 | 8.90 | 11.40 |
| 18 | 8.10 | 10.20 | 13.10 |
| 24 | 9.00 | 11.50 | 14.80 |
| Range | Meaning | Typical action |
|---|---|---|
| Below P3 (~3rd percentile) | Only ~3% of reference babies weigh less — may warrant clinical review if persistent or with poor feeding | Discuss with pediatrician; do not panic from one reading |
| P3–P15 | Lower end of typical range; many healthy infants track here | Plot trend over 2–3 visits |
| P15–P85 | Middle of the distribution — most healthy babies | Routine care unless other concerns |
| P85–P97 | Heavier than average for age; often normal with tall parents | Watch for rapid jumps crossing multiple percentile lines |
| Above P97 (~97th) | Only ~3% weigh more — can be constitutional or need context | Clinician may assess length, feeding, and family pattern |
Interpolate P3, P50, P97 at age (months)
σ ≈ (P97 − P3) / 3.76
z = (weight_kg − P50) / σ
percentile ≈ Φ(z) × 100
Based on breastfed infants in optimal conditions; common globally and in many US practices for infancy
US reference including older children; some clinics use WHO for under 2 and CDC after
Smoothed P3/P50/P97 anchors inspired by WHO weight-for-age — not byte-identical to official LMS plots
Percentile: 65.4% · P50 3.3 kg
Middle range
21.8% at 5.2 kg (P50 5.8 kg) · 4.5 kg → 4.6%
58.5% · band P3–P97: 7.8–11.3 kg
11.79 kg → 57.5% · P50 11.5 kg
Share with new parents tracking growth between visits
Suggested hashtags: #Baby #Parenting #WHO #GrowthChart #Calculator