Short answer
In the UK, weight-loss surgery is generally considered for adults with a body mass index (BMI) of 40 or more, or 35 to 39.9 with a serious health condition that weight loss could improve, such as type 2 diabetes or high blood pressure. Thresholds are lower for some ethnic backgrounds and for people with recently diagnosed type 2 diabetes. BMI alone does not decide it: a specialist team also assesses physical and mental health, eating patterns, fitness for surgery and willingness to commit to lifelong follow-up.
Key points
- UK starting points: BMI 40 or more, or 35 to 39.9 with a significant weight-related condition.
- Thresholds are 2.5 points lower for people of South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean background.
- Recent-onset type 2 diabetes can bring an assessment forward, from a BMI of 30 in some cases.
- Agreeing to long-term follow-up after surgery is part of the criteria.
- US and international surgical societies use somewhat lower thresholds than UK guidance.
The UK criteria
BMI is weight in kilograms divided by height in metres squared. The National Institute for Health and Care Excellence (NICE) recommends offering referral to a specialist weight-management service for adults with a BMI of 40 or more, or between 35 and 39.9 with a significant health condition that could improve with weight loss, provided they agree to the long-term follow-up needed after surgery.1 Examples given include cardiovascular disease, high blood pressure and type 2 diabetes, and the list is not exhaustive.1
The NHS describes the same thresholds and lists conditions such as high blood pressure, diabetes, arthritis, breathing problems and asthma. It also says you need to agree to make healthy lifestyle changes and attend regular check-ups after surgery, and that availability varies across the UK.2
| Situation | General threshold | Lower threshold for listed ethnic backgrounds |
|---|---|---|
| BMI alone | 40 or more1 | 37.5 or more3 |
| BMI with a significant weight-related condition | 35 to 39.91 | 32.5 to 37.43 |
| Recent-onset type 2 diabetes (diagnosed within 10 years) | Expedited assessment offered from 35; considered from 30 to 34.91 | Considered at a threshold 2.5 lower1 |
Why thresholds differ by ethnic background
NICE advises considering referral at a BMI 2.5 points lower for people of South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean family background. The reason given is that these groups tend to carry more fat around the middle and have a higher risk of heart and metabolic disease at lower BMI levels.1
The NHS applies the same adjustment to its definition of obesity: for these groups, a BMI of 27.5 or higher counts as obese, compared with 30 for others.3
The type 2 diabetes route
NICE treats recent-onset type 2 diabetes, meaning diagnosed within the past 10 years, as a reason to speed things up. It recommends offering an expedited (faster-track) assessment from a BMI of 35 and considering one at a BMI of 30 to 34.9, as long as the person is also being assessed in, or will be assessed in, a specialist service.1 Our page on bariatric surgery and type 2 diabetes remission looks at the outcomes.
What the assessment looks at beyond BMI
Meeting a BMI threshold makes someone eligible for assessment, not automatically for an operation. NICE says the specialist team should assess medical needs, nutritional status, psychological needs, previous attempts at weight management and fitness for anaesthesia and surgery, along with practical factors such as language barriers and deprivation that may affect outcomes.1
The NHS describes three strands. Physical health checks include blood and urine tests, X-rays and scans for problems such as blood clots, ulcers and hernias. A mental well-being assessment looks at the ability to cope with the long-term lifestyle changes, keep follow-up appointments and take supplements. A review of eating patterns covers how you have already tried to lose weight. The results decide whether surgery is suitable and which type is recommended.4
That focus on long-term commitment reflects what comes afterwards: lifelong supplements and monitoring. See why vitamin supplements are needed for life.
How international criteria differ
In 2022, the American Society for Metabolic and Bariatric Surgery (ASMBS) and the International Federation for the Surgery of Obesity and Metabolic Disorders (IFSO) updated their indications. They recommend surgery for people with a BMI over 35 regardless of whether they have related conditions, and say it should be considered at a BMI of 30 to 34.9 with metabolic disease. For Asian populations, they suggest surgery should be offered above a BMI of 27.5, and they state that appropriately selected children and adolescents should be considered.5
These are professional-society recommendations and do not determine access in any particular health system. Someone told they qualify under one set of criteria but not another should ask which framework is being applied and why.
If surgery is not the right fit
The NHS lists other treatments for obesity: a calorie-controlled balanced diet, regular physical activity, and weight-loss medicines such as semaglutide, tirzepatide and liraglutide, which reduce appetite, or orlistat, which reduces fat absorption, usually prescribed alongside diet and lifestyle advice.3 How these compare with surgery is covered in weight-loss injections vs surgery.
Common questions
Do I have to have tried other ways of losing weight first?
Neither the NHS nor NICE pages describe a fixed rule, but the assessment does look at previous weight-loss attempts.14
Can I qualify with a BMI of 35 and no other health problems?
Under UK guidance, usually not, because a BMI of 35 to 39.9 needs a significant weight-related condition; ASMBS and IFSO recommend surgery above 35 regardless of other conditions.15
Can I pay privately if I do not meet NHS criteria?
The NHS notes that surgery can be paid for privately.2 A responsible surgical team would still be expected to carry out a full assessment of suitability.
Does the type of operation depend on the assessment?
Yes; the NHS says the assessment results are used to decide which type of surgery is recommended.4 See gastric sleeve vs gastric bypass.
Bottom line
BMI thresholds of 40, or 35 with a significant weight-related condition, are the usual UK starting point, with lower thresholds for some ethnic backgrounds and for recent-onset type 2 diabetes. Qualifying on numbers opens the door to a specialist assessment; suitability depends on that assessment and on readiness for lifelong follow-up.
Related reading
- Bariatric surgery overview
- Gastric sleeve vs gastric bypass: how do they compare?
- Weight-loss injections vs surgery: how do they compare?
- Can bariatric surgery put type 2 diabetes into remission?
- What is a gastric balloon?
Sources
- National Institute for Health and Care Excellence. Overweight and obesity management (NG246): medicines and surgery. NICE; 2025. https://www.nice.org.uk/guidance/ng246/chapter/Medicines-and-surgery. Accessed 5 November 2026.
- NHS. Weight loss surgery: why it’s done. NHS website. https://www.nhs.uk/tests-and-treatments/weight-loss-surgery/why-its-done/. Accessed 5 November 2026.
- NHS. Obesity: treatment. NHS website. https://www.nhs.uk/conditions/obesity/treatment/. Accessed 5 November 2026.
- NHS. Weight loss surgery: preparing. NHS website. https://www.nhs.uk/tests-and-treatments/weight-loss-surgery/preparing/. Accessed 5 November 2026.
- Eisenberg D, Shikora SA, Aarts E, et al. 2022 American Society of Metabolic and Bariatric Surgery (ASMBS) and International Federation for the Surgery of Obesity and Metabolic Disorders (IFSO) indications for metabolic and bariatric surgery. Obesity Surgery; 2023;33(1):3-14. https://pubmed.ncbi.nlm.nih.gov/36336720/
Article history
- — First published.