Average baby weight

During 2019-2020, 84% of babies who had their weight recorded weighed anywhere between 2.5 and 3.9kg1 at birth. Only 7% of babies recorded had a low birthweight of less than 2.5kg^1.

There are many factors that can influence how much your baby weighs at birth. Your diet and nutrition during pregnancy, the length of your pregnancy and the physical build of both biological parents, being just a few examples¹.

The bottom line? Babies come in all shapes and sizes, just like their parents.

From birth, your baby’s weight and growth will be measured regularly by a healthcare professional. The results will be recorded in your baby’s personal child health record (PCHR), more commonly known as the ‘red book'. This contains a baby weight chart to make sure your baby’s growth and weight is right on track.

Exactly how often your baby will be weighed depends on their age. As a general rule, if there are no health problems or concerns after the first two weeks of your baby’s birth, they should be weighed²:

• Once a month up to 6 months of age
• Once every two months from 6 to 12 months of age
• Once every three months over the age of 12 months

The first thing to know is that it’s completely normal for babies to lose weight in the first few days following their birth. In fact, many babies lose up to 10% of their birth weight³.

Once breastfeeding or bottle-feeding is established, and your baby is latching on well and feeding regularly, they should start gaining weight again. Babies generally get back up to their original birth weight within 10–14 days of being born¹.

Growth is a good indicator that your baby is healthy. If they’re growing and gaining weight, then that’s a good sign that everything’s as it should be and that there’s nothing for you to worry about.

If your baby isn’t gaining weight, then this can sometimes be a sign that there’s a problem. That’s why your baby’s weight will be carefully monitored during the first couple of months, to make sure that they’re developing healthily and growing as they should.

It’s very important for you to attend all of your baby’s clinic appointments, and that you speak with your midwife or GP if you’ve got any concerns at all about your baby’s weight gain, growth and development.

Baby growth is measured using what’s known as a centile chart. This is a guide to your baby’s very own individual weight gain, rather than comparing it to that of other babies. 

Each baby will have their own growth chart in their red book, and three of the things that are normally measured are: weight, length, and head circumference.

A centile chart shows the growth pattern that healthy children normally follow, irrespective of whether they’re breastfed, formula fed or a mixture of both. There are different charts for boys and girls. That’s because in general, boys tend to be a little heavier and have growth patterns different to those of girls.

Babies who are born before 37 weeks of pregnancy will follow a different chart until two weeks after their original due date. After that, the standard boy/girl charts will be used, applying a correction factor.

The growth centiles on a baby weight chart show the average weight gain for babies of different ages, and you’ll see your baby grow most rapidly in the early months of their life. 

Don’t be too concerned if your baby starts off at the top or the bottom end of the baby weight chart - this doesn’t mean they are over or underweight.

What your health visitor will look for is a steady rate of weight gain, along a given line called a centile on the growth chart. This is individual to your baby. Your baby’s weight and height may not follow the same centile line all the time, and that’s OK. It can sometimes happen that the measurements go down or up by one centile.

However, if your baby’s measurements change by two centiles, this is less common and if it happens, it’s probably worth discussing this with your doctor or health visitor in order to rule out any health issues.

Remember that all babies are different – even siblings. Try not to compare your baby to others and focus on how much they’re growing and changing every day! 

Growth charts can be sometimes overwhelming and confusing. The main thing to remember is that if your doctor is happy with your baby’s growth and weight gain, there’s nothing for you to be concerned about.

By the time they’re six months old, your baby is likely to weigh twice as much as they did at birth. Usually, your baby will gain most of their weight between six and nine months of age. Their growth will then gradually slow down, as they become more active as toddlers.

Occasionally, your baby’s weight may increase or decrease at a higher rate than normal. This could be caused by sudden growth spurts or bouts of illness. Your baby's weight can also fluctuate around the start of weaning, when they may have difficulty accepting solids, or when they become more mobile and their activity levels increase.

A general trend of good weight gain is a sign that your baby is growing well, and meeting their early milestones for a lifetime of healthy development. If you have any concerns about your baby's weight gain, talk to your health visitor.