HealthInfo Canterbury
Finding out if I am a healthy weight
Working out your body mass index (BMI) is a good way to find out if you're 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, and 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're tall, an athlete or muscular
- underestimate body fat if you're short, 70 or older or you've lost muscle.
Working out your BMI
You can work out your BMI using the following online BMI calculator from the Ministry of Health. You'll need to know your weight in kilograms and your height in centimetres. The calculator will tell you if you're underweight, a healthy weight, a slightly unhealthy weight or 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 rest of the information on this page.
Your BMI result
Underweight (less than 18.5)
Being underweight could be a sign that you aren't eating enough or you have an underlying health issue. Make an appointment to see your GP or practice nurse. Find out more in How to gain weight.
Healthy weight (18.5 – 24.9)
Keep up the good work. For tips on maintaining a healthy weight see Eating well and keeping active for good health.
Slightly unhealthy weight (25 – 29.9)
The best way to lose weight is by eating fewer calories than you need and being more active. Find out more in How to lose weight.
Very unhealthy weight (30 and over)
The best way to lose weight is by eating fewer calories than you need and being more active. Find out more in How to lose weight.
If you're concerned about your weight, talk to your GP or practice nurse.
Your waist size also matters
Measuring your waist is a good way to check that you don't 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. You may need someone to help you with this.
To measure your waist:
- find the top of your hip bone and the bottom of your ribs (this is usually at the level of your belly button)
- wrap a tape measure around your waist midway between these points
- breathe out normally before taking the measurement
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're a man
- 80 cm (31.5 in) or more and you're a woman.
If your waist is:
- 102 cm (40 in) or more and you're a man
- 88 cm (34 in) or more and you're a woman
you're at very high risk and should talk to your GP or practice nurse.
Written by HealthInfo clinical advisers. Last reviewed April 2020.
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See also:
Review key: HIDIN-36726
