Adjusting for maturity

We have developed a spreadsheet to calculate maturity adjusted BMI percentiles for any child for whom you know their height and weight, plus the heights of both (biological) parents. It’s a non-invasive, reliable method of assessing a child’s stage of development that allows you to consider their weight relative to others of their biological age, in addition to those of the same chronological age. The spreadsheet calculates a child’s level of maturity (i.e., if they are early, on-time, or late – and by how much) from the % of their expected adult height they have so far achieved, vs what is usual for children their age (relative to UK 1990 growth charts). It provides an adjusted BMI percentile which you can compare with the standard percentile (i.e., for children of their age in months), to take into account when advising parents whether or not their child’s weight is of concern.

This screenshot shows how the calculator works (along with these instructions!). You just enter the values you have in the pale green boxes on the left, click on submit, and the results are generated on the right. You can see the BMI of the child, the percentile of this BMI relative to other children of their age, and an adjusted BMI for their level of maturity. In this example, the top row of boxes on the right indicates that this boy is a slightly early maturer, and as such adjusting for maturity there is a slight change to his BMI percentile. But according to both the standard and adjusted measure, he is a healthy weight for his age.


When we adjusted for maturity for a cohort of 450 UK Year 6 children (age 10-11), we found that early maturing children were far more likely to be  classified as overweight or obese than their on-time or late maturing peers; 32% of overweight girls and 15% of overweight boys would have been considered a healthy weight using maturity adjusted BMI percentiles, and 11% and 8% of obese girls and boys respectively being reclassified as overweight.

This reclassification system is already used in sporting organisations – to adjust competition to children of more equal stages of physical development, and ensure late-maturing children are not overlooked. In the health setting, it may help us to consider whether the greater BMIs of early maturing children are a real indication of health risk, or just a function of their advanced stage of pubertal development.

Unfortunately the calculator to adjust BMI percentiles for maturity status is on excel, which is not supported by this website – we’re working on solving this, but we’d be happy to send it to you by email if you send through a request on the form below:


These three stories have been designed to communicate to parents why it may be important, beneficial, and not as difficult as they may imagine to take steps towards helping their child to achieve a healthy weight. They have been designed with health communication in theory in mind, to try and reduce parents’ defensiveness, promote confidence and reduce the stigma or being told your child is overweight. They are available in a pdf format, designed to be printed as a leaflet or postcard-sized letter insert – see the picture below.


Louise’s story: Designed to provide an example of a parent who finds it initially hard to
accept that their child is overweight, and worries that by talking to her about h
er weight she may harm her child’s well being. The case study aims to model a situation where the parent does take a positive step towards trying to improve the family’s diet
and lifestyle, and has a positive experience; small steps are good enough to make a difference, and possible to accommodate within family

shutterstock_mother and son talking

Mark’s story: Designed to give a child’s perspective of what it may be like to know you are overweight, but not to receive support or involvement from your parents. Children’s perspectives are very rarely considered – beyond presu
ming that to mention overweight is to risk undermining their self-esteem. This story aims to put across the potential benefits to come from engaging with a child about their weight and the positive (rather than stigmatizing) benefits of engaging with children’s weight management services.

Sam’s story
: Very often the parents of an overweight child are overweight themselves, with the effect that parents lack the belief that they can do anything to a make a difference to their child’s weight and feel it is inevitable that their child will be overweight too. The aim of this scenario is to encourage all parents to try and help their child, and believe that taking steps with their child now, may help them to avoid being overweight later in life.

Download a pdf of these narrative messages