Baby Percentile Calculator
Compare your baby's weight, length, and head circumference with WHO growth standards (0–24 months).
Enter completed months (e.g., 6.5 for 6 months + 2 weeks).
Weight
Length & head circumference
Optional but recommended.
How to Use This Calculator
Measure carefully
Weigh your baby without clothing or diaper for the most accurate result. Measure length lying flat using a firm surface and a measuring tape.
Select age and sex
Percentiles differ for boys and girls. Enter age in completed months; you can use decimals for extra weeks (e.g., 6.5).
Review results with your pediatrician
Percentiles show how your baby compares with peers. Any concerns about rapid changes or extreme percentiles should be discussed with a healthcare professional.
Formula
Percentile = Φ((measurement − reference mean) / standard deviation) × 100
Example: 6-month-old boy weighing 8.0 kg. WHO average ≈ 7.9 kg. Estimated SD ≈ 1.0 kg. Z-score = (8.0 − 7.9) / 1.0 = 0.1. Z = 0.1 corresponds to the 53rd percentile → slightly above average weight for age.
About the Baby Percentile Calculator
This tool uses World Health Organization (WHO) growth standards to estimate how your baby's measurements compare with healthy peers worldwide. These standards are based on babies who were predominantly breastfed and raised in ideal conditions, making them suitable for most infants regardless of geography or ethnicity.
Monitoring weight, length, and head circumference together gives the best picture of nutritional status and brain growth. Percentiles help you understand trends over time, not just single readings. Staying on a consistent curve usually indicates healthy growth.
Why track baby percentiles?
- Spot early signs of feeding issues or growth faltering.
- Ensure catch-up growth for preterm infants is on track.
- Support discussions with pediatricians about nutrition and development.
- Document progress for well-child visits and medical records.
Limitations
- Percentiles are statistical comparisons, not health diagnoses.
- Babies born premature should use corrected age until 24 months.
- Large shifts in percentile bands matter more than single data points.
Frequently Asked Questions
Is the 50th percentile the “ideal”?
No. The 50th percentile represents the statistical middle. Healthy babies regularly fall anywhere between the 5th and 95th percentiles.
My baby was premature. How do I use this calculator?
Subtract the number of weeks born early from your baby's age to get the corrected age (until 24 months). Enter that corrected age to compare with term-born peers.
What if one measurement is much higher than the others?
Imbalances (e.g., very high weight but low length percentile) may signal the need for further evaluation. Track trends and discuss concerns with your pediatrician.
How often should I measure at home?
Routine well-child visits provide trustworthy measurements. Monthly home checks are fine, but daily weighing can be misleading due to natural fluctuations.
Do formula-fed babies follow different charts?
WHO standards are suitable for all infants. Formula-fed babies may track slightly differently, but trends over time are more important than exact percentile.