Baby Percentile Calculator
Enter age as a whole number of months (0–36)
Enter only if baby was born premature (< 37 weeks). Used to calculate corrected age.
Optional — leave blank to skip weight percentile
Optional — use recumbent length (lying down) for babies under 2 years
Optional — measure around the largest part of the head (above eyebrows and ears, over the occipital prominence)
Enter Baby's Measurements to Calculate
Select sex, enter age, and add at least one measurement (weight, length, or head circumference) to see growth percentiles.
How to Use the Baby Percentile Calculator
Select Sex and Enter Age
Start by selecting whether your baby is a boy or a girl — sex matters because WHO and CDC growth charts are sex-specific, with separate reference populations for males and females. Then enter your baby's age. You can type the age directly in whole months (0–36) or switch to date entry mode, where you enter the date of birth and the date of measurement, and the calculator automatically computes the exact age in months. If your baby was born prematurely (before 37 weeks), enter the gestational age at birth to enable automatic corrected-age adjustment.
Enter One or More Measurements
Enter any combination of weight, length, and head circumference. All three are optional — you only need to enter the measurements you have available. Toggle between metric (kg, cm) and imperial (lbs/oz, inches) using the unit switch at the top. Accurate measurements produce accurate results: use a calibrated baby scale for weight, a flat measuring board for recumbent length (baby lying down), and a non-stretchable tape measure placed around the largest part of the head for head circumference.
Review Percentile Results and Z-Scores
Results appear instantly as you type. For each measurement you entered, you will see the percentile rank (e.g., 72nd percentile), the Z-score, an interpretation label (normal, low-normal, very low, etc.), and a visual percentile band chart showing exactly where your baby falls across the five growth zones: below 3rd, 3rd–10th, 10th–90th (normal), 90th–97th, and above 97th. Special warnings appear for head circumference values above the 97th (macrocephaly) or below the 3rd (microcephaly) percentile.
Export or Print Results for Your Pediatrician
Use the Print Results button to generate a clean, printer-friendly summary of all percentile results — ideal for keeping in your baby's health records or sharing with your pediatrician at the next visit. The Export CSV button downloads your measurements and results in a spreadsheet format for easy tracking over time. The data source (WHO or CDC) is clearly labeled in the results, along with a note about corrected age if applicable.
Frequently Asked Questions
What is a normal baby percentile range?
Any percentile between the 3rd and 97th is considered within the typical reference range for baby growth charts. This means that 94% of all healthy babies fall within this range at any given measurement. A baby at the 5th percentile may be perfectly healthy — they are simply naturally smaller than most of their peers. Similarly, a baby at the 95th percentile is not necessarily overweight. What matters most is consistency over time: a baby following the same percentile curve at each checkup is growing normally, regardless of whether that curve is at the 10th percentile or the 90th. Growth percentiles are comparison tools, not diagnostic scores.
My baby is in the 10th percentile — is that unhealthy?
No — the 10th percentile is within the normal range and is entirely consistent with healthy growth. By definition, 10% of all babies of that sex and age weigh less than your baby at this percentile, which means your baby is among the smaller but fully normal range of typical infants. The 10th percentile only becomes a concern if it represents a drop from a previously higher percentile (called crossing percentile lines downward), if other measurements like length and head circumference are also low, or if the baby shows other signs of poor feeding or inadequate weight gain. A single measurement at the 10th percentile, especially in a baby whose parents are naturally small, is rarely concerning on its own.
What is the difference between WHO and CDC growth charts?
The WHO Child Growth Standards (2006) and CDC Growth Reference Charts (2000) differ in both the populations they studied and their intent. WHO charts are prescriptive — they describe how children grow under optimal conditions including breastfeeding, non-smoking households, and no nutritional deprivation — across six geographically and ethnically diverse countries. Because they reflect optimal growth, they are recommended as the international standard for children under 2 years. CDC charts are descriptive — they show how a representative sample of US children grew in the 1980s and 1990s, including formula-fed infants and those from diverse socioeconomic backgrounds. The American Academy of Pediatrics recommends using WHO charts from birth through age 2, then CDC charts from ages 2 through 20. This calculator follows that recommendation automatically.
How do I calculate corrected age for a premature baby?
Corrected age (also called adjusted age) accounts for the fact that premature babies have had less time to develop than full-term babies of the same calendar age. To calculate corrected age, subtract the number of weeks early the baby was born from their chronological age. For example, a baby born at 32 weeks gestation (8 weeks early) who is now 5 months old (20 weeks chronological age) has a corrected age of 12 weeks, or approximately 3 months. The formula is: corrected age in months equals chronological age in months minus the weeks of prematurity divided by 4.33. Most guidelines recommend using corrected age for all growth assessments until 24 months corrected age for weight and length, and until 36 months corrected age for head circumference. This calculator performs this adjustment automatically when you enter gestational age at birth.
What does head circumference percentile tell me?
Head circumference percentile reflects the rate of brain and skull growth. The brain grows most rapidly in the first two years of life, making head circumference one of the most clinically important measurements in early infancy. A normal head circumference tracks between the 3rd and 97th percentile and follows a consistent growth curve. A head circumference consistently below the 3rd percentile is called microcephaly and may indicate reduced brain growth, which can be associated with neurological conditions and warrants pediatric evaluation. A head circumference above the 97th percentile is called macrocephaly and may reflect familial large head size (common and benign), hydrocephalus, or other conditions. A head that is growing too rapidly — crossing multiple percentile lines upward — is more concerning than one that has consistently been large. Always discuss unusual head circumference measurements with your pediatrician.
How often should I track my baby's growth?
The American Academy of Pediatrics recommends well-child visits at specific ages in the first two years: at birth (hospital), 3–5 days, 1 month, 2 months, 4 months, 6 months, 9 months, 12 months, 15 months, 18 months, and 24 months. Growth measurements are taken at every well-child visit. After age 2, annual well-child visits are recommended. Between scheduled visits, growth monitoring at home is reasonable for parents who want to track trends, but remember that a single measurement without the longitudinal context of previous data points is difficult to interpret. Consistent measurement technique is essential — variations in how measurements are taken between sessions can create artificial-looking changes in percentiles. This calculator is most useful when used consistently at each well-child visit so you can build a picture of your baby's growth trajectory over time.