Print this topic

HealthInfo Waitaha Canterbury

Finding out if my child is a healthy weight

He aha te taumaha hauora o tāu tamaiti?

Children come in different shapes and sizes – big, tall, small and short. There is a wide range of healthy shapes and sizes.

Children who stay a healthy weight tend to be fitter, healthier, better able to learn and more self-confident. They're also much less likely to have health problems later in life.

The body mass index (BMI) is a way to find out if your child is the right weight for their height.

Positive body talk

To help your child have a positive body image, do not compare their body to others. Talk about the amazing things their body can do – run, jump, skip, tickle – not what their body looks like. Role-model this in the way you talk about your own body and other people's. All bodies deserve respect. See the video in the recommended links below.

Finding out my child's BMI

If your child is at least two years old, you can work out their BMI using an online BMI calculator. You need to use a calculator that is suitable for children, as BMI is measured differently for adults. You'll need to know your child's weight in kilograms and their height in centimetres. The calculator will tell you if your child is underweight, a healthy weight or an unhealthy weight for their height and age.

After giving the BMI result, the calculator provides practical information about what the result means. You should also take a note of the BMI result and read the information below.

You can use the following online BMI calculator from the Ministry of Health.


BMI result

BMI calculators for children give the results as a percentile. This shows how your child's BMI compares to other children of the same sex and age. For example, a girl on the 80th percentile has a BMI score higher than 80 out of 100 other girls her age.

Regardless of your child's BMI result, if you have concerns about their eating, activity levels, sleep, screen time or overall wellbeing, talk to your GP or practice nurse. They will be able to check for any underlying health conditions and may be able to refer your whānau/family to a healthy lifestyle programme for extra support.

Underweight (on the 2nd percentile or below)

If your child is underweight, it might be because they have inherited this from you or their other parent. But it could mean they aren't eating enough, or they have an underlying health issue. Make an appointment to see your GP or practice nurse. Find out more in Underweight children.

Healthy weight (between the 2nd and 91st percentiles)

Your child is likely to be a healthy weight for their height. Aim to instil healthy habits in your whānau/family so you and your children can enjoy good health for life. See Healthy & active children.

Unhealthy weight (91st percentile or above)

If your child is an unhealthy weight, they're more likely to develop health problems. These could include high blood pressure, type 2 diabetes, breathing problems and joint pain. They're also more likely to become an overweight adult.

See Healthy & active children for tips on how to encourage your child to eat well and be more active. If you're concerned about your child's weight, talk to your GP or practice nurse. If your child is 12 or under with a BMI at the 91st percentile or higher, they may be referred to a healthy lifestyle programme.

If your child is an unhealthy weight and still growing, they do not need to lose weight. Staying the same weight while they grow taller will mean they will become a healthier weight for their height over time.

  HealthInfo recommends the following videos

Written by HealthInfo clinical advisers. Last reviewed September 2021.


Page reference: 298107

Review key: HIHEC-62690