A BMI of 40 is classed as severe obesity (class 3) for most adults (NHS). For people of South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean background it is classed as severe obesity (class 3) (NICE). The healthy range is 18.5 to 24.9.
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What a BMI of 40 means
Body mass index (BMI) compares your weight with your height. A BMI of 40 means you weigh 40 kilograms for every square metre of your height. Using the NHS categories, a BMI of 40 is classed as severe obesity (class 3) for most adults.
Most adults
BMI 40 = severe obesity (class 3). NHS ranges: under 18.5 underweight, 18.5–24.9 healthy, 25–29.9 overweight, 30+ obesity.
South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean
BMI 40 = severe obesity (class 3). NICE uses lower cut-offs of 23 and 27.5 because health risks start at a lower BMI.
Your BMI is 15.1 points above the top of the healthy range (24.9). For comparison, the average BMI of adults in England is 27.6 (Health Survey for England 2022), and 64% of adults have a BMI of 25 or more.
Weight at a BMI of 40 for every height
Find your height to see the weight that gives a BMI of 40, in kilograms, stones and pounds. The last column shows the top of the healthy range (BMI 24.9).
| Height | Weight at BMI 40 | Stones & pounds | Pounds | Healthy limit |
|---|---|---|---|---|
| 4′10″ (147 cm) | 86.8 kg | 13 st 9 lb | 191 lb | 54.0 kg |
| 4′11″ (150 cm) | 89.8 kg | 14 st 2 lb | 198 lb | 55.9 kg |
| 5′0″ (152 cm) | 92.9 kg | 14 st 9 lb | 205 lb | 57.8 kg |
| 5′1″ (155 cm) | 96.0 kg | 15 st 2 lb | 212 lb | 59.8 kg |
| 5′2″ (157 cm) | 99.2 kg | 15 st 9 lb | 219 lb | 61.8 kg |
| 5′3″ (160 cm) | 102.4 kg | 16 st 2 lb | 226 lb | 63.8 kg |
| 5′4″ (163 cm) | 105.7 kg | 16 st 9 lb | 233 lb | 65.8 kg |
| 5′5″ (165 cm) | 109.0 kg | 17 st 2 lb | 240 lb | 67.9 kg |
| 5′6″ (168 cm) | 112.4 kg | 17 st 10 lb | 248 lb | 70.0 kg |
| 5′7″ (170 cm) | 115.8 kg | 18 st 3 lb | 255 lb | 72.1 kg |
| 5′8″ (173 cm) | 119.3 kg | 18 st 11 lb | 263 lb | 74.3 kg |
| 5′9″ (175 cm) | 122.9 kg | 19 st 5 lb | 271 lb | 76.5 kg |
| 5′10″ (178 cm) | 126.5 kg | 19 st 13 lb | 279 lb | 78.7 kg |
| 5′11″ (180 cm) | 130.1 kg | 20 st 7 lb | 287 lb | 81.0 kg |
| 6′0″ (183 cm) | 133.8 kg | 21 st 1 lb | 295 lb | 83.3 kg |
| 6′1″ (185 cm) | 137.5 kg | 21 st 9 lb | 303 lb | 85.6 kg |
| 6′2″ (188 cm) | 141.3 kg | 22 st 4 lb | 312 lb | 88.0 kg |
| 6′3″ (190 cm) | 145.2 kg | 22 st 12 lb | 320 lb | 90.4 kg |
| 6′4″ (193 cm) | 149.1 kg | 23 st 7 lb | 329 lb | 92.8 kg |
| 6′5″ (196 cm) | 153.0 kg | 24 st 1 lb | 337 lb | 95.2 kg |
| 6′6″ (198 cm) | 157.0 kg | 24 st 10 lb | 346 lb | 97.7 kg |
A BMI of 40 for women and men
The NHS uses the same BMI categories for women and men, so a BMI of 40 is severe obesity (class 3) whether you are male or female. What differs is body composition: at the same BMI, women usually carry more body fat than men, and men tend to carry more fat around the waist.
BMI 40 for a woman
A 5′4″ (163 cm) woman with a BMI of 40 weighs about 105.7 kg (16 st 9 lb). To reach a BMI of 24.9 she would need to lose about 39.9 kg (6 st 4 lb). After the menopause, fat tends to move towards the waist, so a waist check is especially useful.
BMI 40 for a man
A 5′10″ (178 cm) man with a BMI of 40 weighs about 126.5 kg (19 st 13 lb). To reach a BMI of 24.9 he would need to lose about 47.7 kg (7 st 7 lb). Very muscular men can have a high BMI without excess fat, which is why waist size matters too.
Is BMI 40 different by age? No – adult BMI categories are the same from 18 onwards. Over 65, a BMI between about 23 and 28 is not usually a concern, and losing weight without trying should always be checked by a GP. Children need a BMI centile instead.
Health risks at a BMI of 40
A BMI of 40 is in the obesity range. The NHS explains that obesity raises the risk of type 2 diabetes, coronary heart disease, stroke, some types of cancer (including breast and bowel cancer), fatty liver disease, osteoarthritis and sleep apnoea. Risks rise further at higher BMI levels and when weight is carried around the waist.
BMI cannot tell fat from muscle, so it is best used with a second measure. NICE recommends a waist-to-height ratio: keep your waist to less than half your height.
What to do next
- Set a first goal of 5% weight loss. That is about 5.3 kg for a 5′4″ woman or 6.3 kg for a 5′10″ man at this BMI.
- Aim for 0.5–1 kg (1–2 lb) a week with a daily deficit of about 600 kcal – use the calorie deficit calculator.
- Move more: build up to 150 minutes of moderate activity a week plus 2 days of strength exercise.
- Use free NHS support: the NHS Weight Loss Plan app, or ask your GP or pharmacist about local weight management services and whether you could be referred to a specialist service.
- Talk to your GP about medical options: NICE recommends weight loss medicines and surgery only at certain BMI levels and with specialist support. For example, surgery is usually considered at a BMI of 40 or more, or 35 or more with a related condition such as type 2 diabetes.
Frequently asked questions
Is a BMI of 40 good?
A BMI of 40 is classed as severe obesity (class 3) for most adults by the NHS. The healthy range is 18.5 to 24.9, so a BMI of 40 is above it.
Is a BMI of 40 obese?
For most adults, a BMI of 40 is severe obesity (class 3). For South Asian, Chinese, other Asian, Middle Eastern, Black African and African-Caribbean adults, NICE classes it as severe obesity (class 3).
How much should I weigh to have a BMI of 40?
It depends on your height. A 5′4″ (163 cm) person would weigh about 105.7 kg (16 st 9 lb), and a 5′10″ (178 cm) person about 126.5 kg (19 st 13 lb). See the table above for every height.
Is a BMI of 40 the same for men and women?
Yes. The NHS uses the same adult BMI categories for men and women, so a BMI of 40 is severe obesity (class 3) for both. Women usually carry more body fat than men at the same BMI.
How much weight do I need to lose from a BMI of 40?
To get to a BMI of 24.9, a 5′4″ woman would need to lose about 39.9 kg (6 st 4 lb) and a 5′10″ man about 47.7 kg (7 st 7 lb). Losing 0.5 to 1 kg a week, that would take roughly 40–80 weeks for the woman. Even a 5% loss brings health benefits.
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Medical disclaimer: this guide is general information for adults and is not a diagnosis or medical advice. bmicalculatornhs.net is independent and not affiliated with the NHS. Speak to your GP, pharmacist or another qualified health professional about your own health. Full disclaimer.