Baby Growth Percentile Calculator
Plot your baby on WHO growth charts. Enter age, weight, and length to see their percentile for 0-24 months — with visual growth chart and friendly explanations.
Baby's Measurements
Important Disclaimer:
This calculator is for informational purposes only and uses WHO growth standards. It is NOT a substitute for professional medical advice. Always consult your health visitor, GP, or paediatrician if you have concerns about your baby's growth, development, or health. Every baby grows at their own pace, and small variations are normal.
What Does a Growth Percentile Actually Mean?
If your baby is on the 50th percentile for weight, it means that out of 100 babies of the same age and sex, your baby would weigh more than 50 of them and less than the other 50. The 50th is the median, not a target. Babies on the 3rd percentile and the 97th are both perfectly normal; what matters is whether they stay roughly on their own line over time, not which line they happen to be on.
Health visitors and paediatricians worry about percentile crossing, not percentile rank. A baby tracking steadily along the 9th percentile is healthier than one who has dropped from the 75th to the 25th in three months. WHO charts (used in the UK from 2009) are based on breastfed babies from six countries who were raised in optimal conditions, so they describe how children grow when nothing is going wrong, not how the average child happens to grow.
When Centiles Are Worth a Real Look
Three situations are worth raising with your health visitor or GP: dropping more than two centile spaces (e.g. 75th down to the 9th), staying flat in weight for more than a month after the early weeks, or a sudden mismatch between weight and length percentiles where one is far higher than the other. None of these mean something is definitely wrong. They just mean it deserves a proper look.
Worked example: a 4-month-old boy weighing 6.8 kg sits around the 25th percentile. If he was born on the 75th and has dropped steadily ever since, the health visitor will probably ask about feeding frequency, wet nappies and milestones. If he has been on the 25th since birth and is alert, peeing, pooing and meeting milestones, that is just his line. Babies are not supposed to all be average.
WHO 50th Percentile Reference (Approximate)
| Age | Boys weight | Boys length | Girls weight | Girls length |
|---|---|---|---|---|
| Birth | 3.3 kg | 49.9 cm | 3.2 kg | 49.1 cm |
| 1 month | 4.5 kg | 54.7 cm | 4.2 kg | 53.7 cm |
| 3 months | 6.4 kg | 61.4 cm | 5.8 kg | 59.8 cm |
| 6 months | 7.9 kg | 67.6 cm | 7.3 kg | 65.7 cm |
| 12 months | 9.6 kg | 75.7 cm | 8.9 kg | 73.7 cm |
| 24 months | 12.2 kg | 87.8 cm | 11.5 kg | 85.7 cm |
Things This Calculator Cannot Do
It cannot diagnose anything. It cannot replace the red book, your health visitor's plotted curve, or a GP appointment. It uses a single 50th-percentile WHO dataset for ages 0 to 24 months and estimates other percentiles from that, which is fine for a quick sanity check but not the same as a proper longitudinal chart with your baby's actual measurements over time.
If you want a fuller picture, weigh your baby on the same scales each time, ideally naked or in a clean nappy, and plot at the same time of day where possible. The personal child health record (red book in England) is still the canonical tool for tracking. If something feels off, even if numbers say otherwise, ring your health visitor; they would rather see you for a non-issue than miss a real one. The [pregnancy due date calculator](/pregnancy-due-date-calculator) and [age calculator](/age-calculator) help you keep track of corrected age, which matters a lot if your baby was born early.
Frequently Asked Questions
My baby is on the 9th percentile. Should I worry?
Almost certainly not on its own. The 9th percentile means 9 out of 100 babies the same age and sex weigh less, and 91 weigh more, but every one of those 9 is normal. Health professionals look at the trend across several measurements rather than a single number. If your baby is alert, feeding well, producing wet nappies and meeting milestones, the line they sit on is just their line.
Why does the UK use WHO charts and not US CDC charts?
WHO charts have been the UK standard since 2009 because they are built from babies raised in optimal conditions across six countries (including breastfed infants), so they show how a child should grow rather than how the average child does grow. CDC charts are descriptive of US children, where formula feeding has historically been more common and so weight gain runs slightly higher. The two charts diverge most noticeably between 3 and 12 months.
What is corrected age and when do I use it?
Corrected age is your baby's age minus the number of weeks they were premature. If your baby was born 8 weeks early and is now 6 months old, their corrected age is 4 months and you plot them at 4 months on the chart. Most paediatricians use corrected age for growth and development until at least 2 years old, sometimes longer for very preterm babies.
Should I weigh my baby every week?
No. After the first six weeks, NHS guidance is to weigh no more than once a month up to 6 months, then every two months until age 1, and every three months in the second year. Weighing too often picks up natural fluctuations that look like problems and aren't. The exception is if a health professional has specifically asked you to monitor more closely.
Why did my baby's weight drop in the first week?
Newborns commonly lose 5 to 10% of their birth weight in the first 3 to 5 days as fluid balance settles and feeding establishes. Most babies are back to birth weight by 10 to 14 days. A loss of more than 10%, or failure to regain birth weight by day 14, is when health visitors will want to investigate feeding properly.
Related Tools
BMI Calculator
Calculate your Body Mass Index with our free BMI calculator. Supports metric and imperial units with a visual scale showing your healthy weight range.
Pregnancy Due Date Calculator
Calculate your estimated due date from your last period or conception date. Track trimester milestones, weeks pregnant and days remaining
Age Calculator
Calculate your exact age in years, months and days. Plus total days alive, zodiac sign, Chinese zodiac, generation and next birthday countdown
Baby Name Generator
Discover the perfect baby name. Filter by gender, style (classic/modern/unique), and starting letter. Build a shortlist of your favorites with meanings.