Baby Weight Percentile Calculator

Tracking your baby's growth is one of the most important ways to ensure they are developing healthily. This free baby weight percentile calculator uses WHO (World Health Organization) weight-for-age growth standards to show exactly where your child falls compared to other children of the same age and sex. Whether you just came from a pediatrician visit and want to understand the numbers, or you want to check between appointments, this tool gives you instant, accurate percentile results.

Step 1: Select Your Baby's Sex

Choose whether your baby is a boy or a girl. This matters because boys and girls follow different growth curves — boys tend to be slightly heavier at most ages during the first three years. The WHO publishes separate growth standards for each sex, and this calculator uses the correct dataset based on your selection.

Step 2: Enter Age in Months

Select your baby's age from the dropdown menu, which covers birth (0 months) through 36 months. Use your baby's age at their last weight measurement. If your baby is between months, pick the closest whole month. For the most accurate results, use the age that corresponds to when the weight was measured, not today's age if different.

Step 3: Enter Weight

Enter your baby's weight in either kilograms or pounds using the unit toggle. You can get an accurate weight from your pediatrician's scale, or weigh yourself holding the baby and subtract your own weight for a home estimate. The calculator accepts decimal values for precision — for example, 7.5 kg or 16.5 lbs.

Step 4: Review the Results

After clicking Calculate Percentile, you will see your baby's exact percentile, z-score, and how their weight compares to the median for their age. The visual growth chart shows standard percentile lines (3rd, 15th, 50th, 85th, and 97th) with your baby's position marked as a dot. A percentile of 50 means your baby weighs more than 50% of children that age. Most healthy babies fall anywhere between the 5th and 95th percentile — what matters most is that they follow a consistent curve over time. The reference table below the chart shows the actual weight values at each standard percentile for easy comparison.

Understanding Growth Percentiles

A single weight percentile measurement is just a snapshot. Pediatricians look at the trend across multiple visits to assess whether a baby is growing consistently along their own curve. A baby who has always been at the 25th percentile is perfectly healthy — that is simply their growth pattern. Concern arises when a baby crosses two or more major percentile lines up or down over a short period. Always discuss growth questions with your pediatrician, as they consider weight alongside length, head circumference, feeding patterns, and developmental milestones for a complete picture.