Baby weight chart by month: birth to 24 months, in kg

Most newborns weigh between 2.5 kg and 4.3 kg at birth if they are boys, and between 2.4 kg and 4.2 kg if they are girls. Those figures are infant weight-for-age from the World Health Organization (WHO) Child Growth Standards, released in 2006, which compares a baby’s weight with other babies of the same age and sex. The range runs from the 3rd to the 97th percentile.

A percentile is a place in a line-up of 100 babies of the same age and sex. A baby on the 3rd percentile is as heavy as or heavier than 3 of them, and a baby on the 97th is as heavy as or heavier than 97, so about 94 in every 100 babies sit between the two. The middle of the range, the median or 50th percentile, is 3.3 kg for a boy and 3.2 kg for a girl.

WHO counts a baby who weighs less than 2.5 kg (2,500 grams) at birth as low birth weight. The full infant weight-for-age chart, in kilogrammes for every month from birth to 24 months, is below, with what each column means and when a number is worth a call to your doctor.

Singapore’s own birth records sit in the same range. These are the single births, babies born one at a time rather than as twins, registered in 2023, from the Immigration & Checkpoints Authority (ICA) yearly report.

Twins are a separate story. ICA’s report notes that twin births “were generally lighter in weight than single births”, and in the same 2023 chart, more than half of the twin babies weighed under 2,500 g.

Baby weight chart by month, birth to 24 months

Find your baby’s age in the first column, then read across to the boys’ or the girls’ columns. Age is in completed months: “Birth” is the day your baby was born, and “3 months” means three full months old. Every weight is in kilogrammes.

Each percentile column places your baby among babies of the same age and sex. HealthHub, the health app and web portal where you can log your child’s growth, explains it with height: a child on the 75th percentile is as tall as or taller than 75% of children of the same age, and the same applies for weight. So the 50th column is the middle of the group, and the 3rd and 97th columns are the edges that 94 in 100 babies sit between.

WHO built the Child Growth Standards from measurements of babies and young children taken in a study of its own, the Multicentre Growth Reference Study. WHO’s infant weight-for-age tables also print the 15th and 85th percentiles; the chart above keeps the 3rd, the 50th and the 97th.

If your baby was born early, the infant weight-for-age chart above is not the one to use. A 2016 review in the Singapore Medical Journal, written for family doctors, says ex-premature babies, meaning babies born early, should be measured on growth charts made for them, so ask your paediatrician which one applies. The first two weeks are tricky for every baby, for the reason in the next section.

The first two weeks: the weight a newborn loses, then gains back

Newborns lose some weight in the days after birth, then gain it back. That means your baby may weigh less at the first check than on the day they were born.

In a study of 961 full-term babies, meaning babies born on time rather than early, published in 2004 in the medical journal Archives of Disease in Childhood, only 26 babies, 3%, lost more than 10% of their birth weight. None of those 26 showed signs of a major disease.

One in five had still not regained their birth weight by day 12. The loss is brief: after day 5, few babies in the study were still more than 10% below their birth weight.

The same study warns that growth charts “are misleading in the first 2 weeks, because they make no allowance for neonatal weight loss”, the weight a newborn loses in those days. The infant weight-for-age chart above goes straight from the Birth row to the 1 month row, with no row for the dip. That is why a weight taken in the first week or two can look low against it.

Feeding is the part you can act on in these weeks. If you are unsure whether feeds are going well, ask whoever weighs your baby, and our guide to lactation consultants in Singapore covers where to get one-to-one help.

That early weigh-in is often the same visit where a nurse or doctor checks for jaundice. Our guide to newborn jaundice in Singapore covers what happens at that review.

How much weight a baby gains each month

Fastest at the start, then slower. In the median (50th percentile) column of the infant weight-for-age chart, a boy goes from 3.3 kg at birth to 4.5 kg at one month and 6.4 kg at three months. A girl goes from 3.2 kg to 4.2 kg, then 5.8 kg.

Spread over the first three months, that is roughly 160 g to 280 g a week, with the most in the first month and the least in the third.

Read the last three rows slowly: each covers more months than the one before. The whole second year adds no more than the first three months did.

Two landmarks fall out of the same line. By 4 months, the median baby weighs about twice their birth weight: 7.0 kg for a boy, 6.4 kg for a girl. By the first birthday it is nearly three times, at 9.6 kg and 8.9 kg.

Treat all of this as the shape of the curve, not a target for your baby. These are steps between rows of the median column, and WHO’s infant weight-for-age tables round each weight to 0.1 kg, so each step can be out by up to 0.1 kg either way. What matters for one baby is whether their own weights keep to a curve over several visits.

Why your Child Health Booklet can show a different percentile

In Singapore, your baby’s weights live in the Child Health Booklet, the “baby book” every child here has been given at delivery since 1984. HealthHub’s page for it, contributed by the Health Promotion Board (HPB), says your child’s height and weight are recorded in it at each well-baby visit, the routine check-up for a healthy baby.

The booklet has a digital companion: the Children’s Health e-service on HealthHub, where you can log birth information and growth records yourself. It sits in both the HealthHub app and the web portal, and HealthHub says the app has the full range of functions.

When you log a weight for a child from birth to 2 years, HealthHub judges it “based on our local growth charts”. It does not tie those local charts to the WHO infant weight-for-age chart.

Singapore has used its own charts for a long time. The booklet’s revised edition of April 2003 printed growth charts that National Healthcare Group (NHG) Polyclinics built from Singapore children measured in 2000. HealthHub does not say whether today’s booklet and app still use them.

Doctors here work with both kinds. The 2016 Singapore Medical Journal review tells family doctors to “use appropriate growth charts from Singapore or the World Health Organization”.

So the same weight can land on a slightly different percentile in your baby’s booklet or app than on the WHO infant weight-for-age chart on this page, because each chart was built from a different group of children. A small gap is not a mistake in either. The useful habit is to compare your baby against the same chart every time, and to go by the one your doctor uses.

When to see a doctor about your baby’s weight

One weigh-in rarely settles anything. The Singapore Medical Journal review says no single measurement on its own appears adequate to spot growth held back by poor nutrition, and that a diagnosis often needs repeated measurements over time.

A low number is not the worry by itself either. The same review counts a child who keeps growing along one percentile line as a normal variant, a healthy pattern rather than a problem, even below the 2nd percentile.

It also describes “catch-down” growth. Some healthy children between 6 and 18 months drift down by up to two of the main percentile lines on a growth chart, to a lower line that suits their genes, then follow that one. The review says these children should still be watched closely.

The thing the review says to treat promptly is failure to thrive, which it defines as “failure to gain weight” or a lack of expected normal growth. Poor nutrition is the most common cause in Singapore, it says, and the reasons it lists include breastfeeding that has not worked and formula made up the wrong way.

For the app’s low and high flags, HealthHub’s own advice is the same: “You may wish to check with and seek advice from your doctors/nurses.”

What to do next

Write every weigh-in into your baby’s Child Health Booklet, or log it in the HealthHub app, and bring it to each visit. HealthHub says the growth charts you enter help your doctors and nurses in their assessment, and a line of weights tells them more than any single number on this page.

The booklet also holds your baby’s immunisation record. Our guide to the childhood immunisation schedule in Singapore sets out which jabs are due, and when.

We do not give medical care at Mother & Baby Singapore, and this page does not replace your baby’s doctor.

Wei Chun

Founder & Editor

A Singapore parent writing the guide he wished he'd had — practical, calm, and grounded in what actually works.

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