HealthInfo Aoraki South Canterbury
Finding out if I am a healthy weight
Te hihira mēnā he taumahatanga hauora tōku
Working out your body mass index (BMI) is one way to find out if you are a healthy weight.
Your BMI estimates how much body fat you have and indicates your risk of getting diseases such as heart disease, type 2 diabetes, stroke and some types of cancer. These are more common in people with more body fat. The higher your BMI, the higher your risk.
Most people over the age of 18 can use the BMI, but it does have some limits. It may:
- overestimate body fat if you are tall, an athlete or very muscular
- underestimate body fat if you are short, 70 or older or have lost muscle
- not be accurate for certain ethnic groups. People of Asian descent can have more body fat on a smaller frame. So, the healthy BMI range would be lower for this group. Māori or Pacific people often have a higher bone density and more muscle mass. For these people, the healthy BMI range would be higher.
Working out your BMI
You can work out your BMI using an online BMI calculator. You will need to know your weight in kilograms and your height in centimetres. The calculator will tell you if you are underweight, a healthy weight, overweight (a slightly unhealthy weight) or obese (a very unhealthy weight).
After giving you your BMI result, the calculator provides practical information about why the result matters. You should also take a note of your BMI result and read the information below.
To work out the BMI for tamariki (children) or rangatahi (teenagers), see Finding out if my child is a healthy weight.
Your BMI result
Underweight (less than 18.5)
Being underweight could be a sign that you are not eating enough, or you have an underlying health issue. Talk to your general practice team. Find out more in How to gain weight.
Healthy weight (18.5 – 24.9)
For tips on maintaining a healthy weight see Eating well for good health and Keeping active.
Unhealthy weight (25 or more)
Not everyone who has a BMI of 25 or more needs to lose weight. This depends on your medical and family history.
For some people who are a very unhealthy weight (a BMI of 30 or more), losing 5 to 10% of their weight will make a big difference to their health and the way they feel. For example, losing 5 to 10 kg if you weigh 100 kg.
If you need to lose weight, the best way to do this is by eating well, being more active, getting enough sleep and managing stress. Talk to your general practice team or dietitian for more information.
Your waist size also matters
Measuring your waist is a good way to check that you do not have too much fat around your stomach. You can have a healthy BMI and still have too much tummy fat, which can also raise your risk of heart disease, type 2 diabetes and stroke.
A waist measurement is not suitable if you are pregnant or have a medical condition where you have swelling of your stomach. It is also not suitable for pēpi (babies), tamariki and rangatahi.
You may need someone to help you measure your waist.
- Stand upright with your feet close together and arms at your side.
- Find the bottom of your last rib and the top of your hip bone (this is usually above your belly button).
- Place the tape measure midway between these two points and wrap it around your waist.
- Relax and breathe in and out normally.
- Take your measurement after breathing out.
No matter what your BMI is or how tall you are, you should try to lose weight if your waist is:
- 94 cm (37 in) or more and you are a man
- 80 cm (31.5 in) or more and you are a woman.
If your waist is:
- 102 cm (40 in) or more and you are a man
- 88 cm (34 in) or more and you are a woman
you are at a very high risk and should talk to your general practice team.
Written by HealthInfo clinical advisers. Last reviewed March 2025.
Sources
See also:
Review key: HIMWA-28082
