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Baby Growth Percentile Calculator
Your baby
An estimate based on the WHO Child Growth Standards, using the LMS method. It is not medical advice and cannot diagnose a growth problem. If you are concerned about your baby’s growth, ask your pediatrician.
Example: a 6-month-old boy weighing 8.0 kg, 68 cm long, with a 43 cm head circumference is at the 53rd percentile for weight, the 57th for length and the 39th for head circumference.
Behind the numbers
How the percentiles are calculated
The calculator compares your baby’s measurements with the WHO Child Growth Standards for babies of the same age in months and sex. For each measurement it takes the published L, M and S values for that age — M is the median, S is the spread, and L adjusts for skew — and turns the measurement into a z-score, which is then converted to a percentile. Ages between whole months are interpolated between the published monthly values.
Worked example: for a 6-month-old boy, the WHO values for weight are L = 0.126, M = 7.93 kg and S = 0.110. At 8.0 kg: z = ((8.0 ÷ 7.93)^0.126 − 1) ÷ (0.126 × 0.110) = +0.08, which is the 53rd percentile. Length: the WHO median for a 6-month-old boy is 67.6 cm, so 68 cm gives z = +0.18, the 57th percentile. Head circumference: the median is 43.3 cm, so 43 cm gives z = −0.27, the 39th percentile.
How to read the result
| Percentile | What it means |
|---|---|
| Below 5th | Smaller than 95 out of 100 peers — worth a check with your pediatrician |
| 5th to 25th | Lower than average, usually still healthy |
| 25th to 75th | Average range |
| 75th to 95th | Above average, usually still healthy |
| Above 95th | Larger than 95 out of 100 peers — worth a check if growth jumped suddenly |
A few comparisons
Example percentiles
| Baby | Weight | Weight percentile | Length | Length percentile | Head | Head percentile |
|---|---|---|---|---|---|---|
| 6-month-old boy | 8.0 kg | 53rd | 68 cm | 57th | 43 cm | 39th |
| 12-month-old girl | 9.0 kg | 52nd | 74 cm | 50th | 45 cm | 53rd |
| 3-month-old boy | 6.0 kg | 30th | 60 cm | 24th | 40 cm | 33rd |
| 24-month-old boy | 12.0 kg | 46th | 88 cm | 52nd | 48 cm | 43rd |
| 6-month-old girl | 7.0 kg | 37th | 66 cm | 55th | 42 cm | 44th |
Tracking growth, not chasing a number.
Measure the same way each time — same scale, baby undressed, length measured lying down — so changes over months are real, not measurement noise.
A baby who follows their own percentile curve steadily is usually growing well, even if that curve sits at the 10th or the 90th percentile.
Babies grow in spurts, so a percentile that dips for one checkup and recovers at the next is common and usually nothing to worry about.
If a percentile drops sharply across two or more checkups, or your baby falls below the 5th percentile, bring the numbers to your pediatrician and ask about it.
Good to know
Your baby growth questions, answered.
What does a growth percentile mean?
A percentile compares your baby with other babies of the same age and sex on the WHO growth standards. A 53rd percentile for weight, like the example on this page, means your baby weighs more than about 53 out of 100 babies their age and sex, and less than about 47.
Is this calculator medical advice?
No. This is an estimate and a screening tool only, based on the WHO Child Growth Standards. It cannot diagnose a growth problem. If you are concerned about your baby’s growth, ask your pediatrician, who can track measurements over time and check for underlying causes.
What percentile is considered normal?
Most healthy babies fall between the 5th and 95th percentiles, and a baby who follows their own steady curve over time is usually fine, even at the 10th or 90th percentile. A sudden drop or jump across percentile lines is more of a reason to talk to a doctor than any single number.
Why WHO standards, and how is this different from the child height percentile page?
The CDC recommends the WHO standards for children under 2, because they describe how healthy breastfed babies grow. This page covers birth to 24 months and all three measurements — weight, length and head circumference. The child height percentile page uses the CDC charts for ages 2 to 20 and height only.