What does my BMI number mean?
Most adults: overweight from 25, obesity from 30. Healthy is 18.5 to 24.9. But your family background can move these lines. For some people, 27.5 already counts as obesity.
On this page
What does my BMI number mean?
For most adults, NICE puts a healthy weight at 18.5 to 24.9. Overweight is 25 to 29.9, and obesity is 30 or more.
- Below 18.5 kg/m²Below the healthy range.
- 18.5 to just under 25 kg/m²Healthy weight.
- 25 to just under 30 kg/m²Overweight.
- 30 kg/m² or aboveObesity, classes 1 to 3.
Sources: NICE NG246; NHS
So for most adults, a BMI of 23 or 24 is healthy. Anything from 25 to 29 is overweight, and 30, 31, 32 or 33 is obesity class 1.
BMI is a quick sort, not a full check of your health. NICE calls it a practical measure to read with caution.
Not sure of your number? Use the NHS BMI calculator, then check whether the lower lines below apply to you.
Why are BMI cut-offs lower for some backgrounds?
NICE says people with a South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean background tend to carry more fat round the middle.
Their risk of heart disease and type 2 diabetes starts at a lower BMI. That’s the line that moves: overweight starts at 23 and obesity at 27.5.
- Below 18.5 kg/m²Below the healthy range.
- 18.5 to just under 23 kg/m²Below the overweight line.
- 23 to just under 27.5 kg/m²Overweight.
- 27.5 kg/m² or aboveObesity.
Sources: NICE NG246; NHS
Think of a lower speed limit outside a school. Same road, earlier limit, because the risk starts sooner.
Going over doesn’t mean harm is coming. It does mean your risk starts climbing at a lower number. So a 24 is overweight here, and a 28 is obesity.
If this is your background, read your result against these lines. The NHS calculator asks about it for this reason.
Is a BMI of 25 to 29 a problem?
It’s above the healthy range. The NHS says overweight raises your risk of type 2 diabetes, heart disease, stroke, high blood pressure and some cancers.
Small changes count. Losing 5 to 10% of your weight can improve your health. At 90 kg, that’s 4.5 to 9 kg.
Your waist adds what BMI can’t see. With a BMI under 35, NICE says to also use your waist-to-height ratio.
Divide your waist by your height, in the same units. A 96.5 cm waist at 170 cm tall gives 0.57.
NICE says 0.5 to 0.59 means increased health risk, and 0.6 or more means further increased risk. The NHS puts it simply: keep your waist under half your height.
This matters at 23 or 24 too. NICE says someone in the healthy range may still carry extra belly fat. Our waist-to-height guide shows how to measure.
What do obesity classes 1, 2 and 3 mean?
The class shows how far above the obesity line your BMI sits. For the backgrounds above, each line is usually 2.5 lower.
| Class | Most adults | South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean |
|---|---|---|
| Class 1 | 30 to 34.9 | 27.5 to usually 32.4 |
| Class 2 | 35 to 39.9 | Usually 32.5 to 37.4 |
| Class 3 | 40 or more | Usually 37.5 or more |
Source: NICE NG246
Why does 35 matter? NICE uses waist-to-height ratio only below 35. At 35 or over, NICE no longer asks for a waist check.
It’s also where surgery can come up. The NHS says you may be offered weight loss surgery at 40 or over. At 35 or over, it may be offered if you also have a condition weight loss could help, such as type 2 diabetes.
For the backgrounds above, those lines are 37.5, or 32.5 with such a condition. Surgery is one option among several, and your GP can talk you through the rest.
When can BMI be wrong?
BMI uses only your height and weight. It’s like judging a suitcase by its weight: it can’t tell books from clothes.
So the NHS says BMI can’t tell muscle from fat. A very muscly person can read as overweight or obese with little body fat.
| Who | Why BMI can mislead | What to do |
|---|---|---|
| Lots of muscle | Muscle adds weight, so BMI can read high. | If your BMI is under 35, check your waist-to-height ratio too. |
| Aged 65 or over | NICE says a slightly higher BMI may protect you when older. | Ask your GP to read it alongside your other health. |
| Pregnant | The NHS adult calculator isn’t for use in pregnancy. | Ask your midwife or GP about your weight. |
| Aged 2 to 17 | Children are compared with others of the same age and sex. | Use the NHS child BMI calculator. |
Sources: NICE NG246; NHS BMI calculator; NHS child BMI calculator
Have, or think you may have, an eating disorder? The NHS says not to use its BMI calculator. Talk to your GP instead.
Losing weight and want to keep your muscle? See keeping muscle while losing weight.
When to speak to a GP
The NHS says to see a GP if your BMI is overweight or above and:
- you want help to lose weight
- your waist is more than half your height
- you have pre-diabetes, diabetes, high blood pressure, joint pain, high cholesterol, sleep apnoea or heart and circulation disease
- obesity runs in your family
- you have, or think you may have, an eating disorder such as binge eating
Pre-diabetes means blood sugar higher than normal, but not yet diabetes. Sleep apnoea is when your breathing stops and starts while you sleep.
A GP can refer you to weight management programmes, medicines or surgery. In some areas you can refer yourself to local weight loss services.
Never stop or change a prescribed medicine without your prescriber. Thinking about weight loss injections? Read blood tests before starting a GLP-1.
Gaining weight without knowing why? See unexplained weight gain and blood tests for weight loss.