Note: This baby weight percentile calculator is the weight-only percentile tool, for checking your baby’s weight against the WHO growth standards, so use the Baby Height and Weight Percentile Calculator instead when you also want to check height, or the Baby Height and Head Circumference Percentile Calculator when you want to check height and head size.
👶 Baby Weight Percentile Calculator
WHO growth standards for babies from birth to 24 months
Growth chart
Saved weigh-ins (on this device)
Baby Weight Percentile Calculator: How It Works
A baby’s weight is one of the easiest ways to see whether growth is on track. This calculator compares your baby’s weight with the WHO Child Growth Standards for babies from birth to 24 months, then shows a percentile, a Z-score and a growth chart.
How to Use the Calculator
- Choose your baby’s gender. Boys and girls have different growth curves.
- Enter the age in months. Use decimals for more accuracy, for example 3.5 for three and a half months.
- Enter the weight and pick kg or lb.
- Add the birth weight (optional) to see how much weight has been gained since birth.
- Press Calculate to see the percentile and the dot on the chart.
- Press Save this weigh-in after each check. Over time the purple line shows your baby’s own growth path. Saved data stays on your own device.
How to Weigh Your Baby at Home
- Use the same scale each time, ideally a baby scale.
- Weigh at a similar time of day, for example before a feed.
- Weigh with no clothes or a clean dry nappy, and subtract the nappy weight if you can.
- Check weight about once a month, or as often as your doctor suggests.
What Does a Percentile Mean?
A percentile compares your baby with other babies of the same age and gender. If your baby is on the 40th percentile, about 40 out of 100 babies weigh less and about 60 weigh more. It is not a score or a grade. A baby on the 10th percentile and a baby on the 90th can both be healthy.
| Percentile | General meaning |
|---|---|
| Below 3rd | Smaller than most babies of the same age. Mention it to your doctor. |
| 3rd to 15th | Lower end of the typical range. |
| 15th to 85th | Middle of the typical range. |
| 85th to 97th | Upper end of the typical range. |
| Above 97th | Larger than most babies of the same age. Mention it to your doctor. |
What matters most is the trend. A baby who follows the same curve over time is usually growing well. A sudden move across several percentile lines is a good reason to speak to a doctor.
Newborns and Early Weight Loss
Many newborns lose a little weight in the first days after birth and then start gaining again, usually regaining birth weight within about two weeks. Because newborn weight changes quickly, ask your midwife or doctor how to read weights in the first weeks.
When to Talk to a Doctor
- Your baby is below the 3rd or above the 97th percentile.
- Your baby’s weight moves across several percentile lines.
- Your baby feeds poorly, has fewer wet nappies than usual, or seems unusually sleepy.
- You are worried for any reason. Trust your instincts.
What Do Baby Weight Percentiles Mean?
A percentile compares a baby with 100 babies of the same age and sex on the WHO growth standards. The 50th percentile is the middle: half of those babies weigh less and half weigh more. For example, a baby at the 25th percentile weighs more than 25 of those 100 babies.
A healthy baby can sit anywhere on the chart, and staying near their own line over time matters more than one single reading. For more detail, see our baby weight percentile guide.
Frequently Asked Questions
Which growth standard does this calculator use?
It uses the WHO Child Growth Standards (2006) for weight-for-age from birth to 24 months, which describe how babies grow in healthy conditions.
Is a low percentile a bad sign?
Not by itself. Healthy babies come in many sizes. Doctors look at the growth pattern over time, feeding, development and the family’s build.
My baby was born early. Can I use this?
This version does not correct for prematurity. Ask your doctor, who will usually use your baby’s corrected age.
Should I weigh my baby every day?
No. Daily weights vary a lot and can cause unnecessary worry. Monthly checks, or the schedule your doctor gives you, are usually enough.
Is my saved data private?
Yes. Saved weigh-ins are stored only in your own browser on your device. They are not sent anywhere. Clearing your browser data will remove them.
What is a Z-score?
A Z-score shows how far a measurement is from the average for the same age and gender. A Z-score of 0 is exactly average, and most healthy babies fall between -2 and +2.
What is a good weight percentile for a baby?
There is no single best percentile. Anywhere between the 3rd and 97th percentile on the WHO chart can be healthy — the pattern over time matters most.
My baby dropped to a lower percentile — should I worry?
Small moves are common. If the weight crosses two or more percentile lines or you are concerned, talk to your baby’s doctor.