How a baby's weight changes as they grow

A baby's weight is a good indicator of their overall health and development, and it can reassure you that they're feeding well.

So, understandably, parents want to keep an eye on their little one to ensure that they're happy and growing healthily.

All babies are different - just like adults - and their weight can be influenced by several factors. These can include their parents' height and weight, their health when born, and their mother's diet during pregnancy.

To help you understand how your baby's weight may change as they grow, we're going to run through how a baby's weight and height are monitored, and how much weight an average baby gains.

How much weight do babies gain per week?

In their first few days following birth, it's normal for babies to lose some weight - up to 10%. This is because they're born with extra fluid which is then lost. Most little ones will be back to or above their birth weight by two weeks old.  

Although weight changes in babies aren't consistent per week, as a rough guide, after returning to their birth weight, babies generally gain around 175g to 225g (6oz to 8oz) each week. 

By around six months, most little ones weigh double what they did at birth and are likely to gain the most weight between six and nine months.

By 12 months, most babies have tripled their birth weight. Once they become active toddlers, the rate of their growth will slow down gradually.

How is my baby's weight gain monitored?

Once they're born, your baby's growth (including their weight, length, and head circumference) will be monitored by their health visitor or doctor and plotted on a growth chart (also known as a centile chart) at regular intervals. Medical professionals use different newborn weight gain charts for baby boys and girls because their growth patterns are slightly different.

During the first two weeks after birth, they'll be monitored to make sure they return to their birth weight. After those early weeks, a baby is usually weighed...

• once a month until they're six months old
• once every two months between the age of six months and one year
• once every three months after their first birthday.

If your doctor says your baby is healthy and growing well, there's usually no reason to worry about their weight. But if there's a possible health issue to be investigated, your baby's growth may be monitored more regularly.

What is the average baby's weight?

This chart is from the WHO (World Health Organisation) and is just a rough guide to the average 50th centile baby weights in their first year. Babies who are born prematurely before 37 weeks are monitored using a slightly different weight chart.

When should I worry about my baby's weight gain?

All babies are different and baby weights under or above the figures stated in the chart above aren't necessarily something to worry about. It's normal for babies to go through a period of not gaining weight or gaining more weight than usual. This can be due to spurts in their growth, a sickness, issues with them adjusting to solid foods, or simply because they burn more calories once they start to become more active.

As with all aspects of parenting, it's good to trust your instincts! So, if you've got any worries about your baby's growth at any stage, don't be afraid to reach out to your doctor or health visitor.