The UK's most complete GLP-1 guide
Every Question Answered. Every Side Effect Explained.
- How GLP-1 medications work
- Mounjaro vs Wegovy compared
- Injection instructions
- Side effects & solutions
- What to eat on treatment
- FAQs answered
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Weight Loss Operations in the UK
Weight loss operations — also called bariatric surgery — are invasive surgical procedures designed to help people with severe obesity lose significant amounts of weight. In the UK, weight loss operations are typically only considered after other weight management approaches have been tried, and they carry both serious risks and potential benefits. This guide explains the main surgical options available through NHS and private healthcare, who qualifies, and how they compare to non-surgical weight loss approaches like prescription weight loss medication and lifestyle changes.
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Enter your height and weight below. Supports both imperial (stone & lbs) and metric (kg). Results include NHS category, healthy weight range, and ethnicity adjustments.
What Is BMI and Why Does It Matter?
Body Mass Index (BMI) is the most widely used screening tool for assessing whether your weight falls within a healthy range. Used by the NHS, GPs, and weight management services across the UK, BMI provides a quick snapshot of your weight relative to your height. The formula is simple: your weight in kilograms divided by your height in metres squared (kg/m²).
While BMI isn't a perfect measure — it doesn't account for muscle mass, bone density, or fat distribution — it remains the standard first step in identifying potential weight-related health risks including type 2 diabetes, cardiovascular disease, high blood pressure, and certain cancers.
The NHS also recommends adjusted thresholds for people of South Asian, Chinese, or Black African heritage — a BMI of 23 or above is classified as overweight, and 27.5 as obese. Our calculator includes this adjustment as a one-click toggle.
Types of Weight Loss Surgery Available in the UK
The NHS offers several bariatric surgery options for people with severe obesity (BMI 40 or above, or BMI 35+ with weight-related health conditions). Gastric bypass reduces stomach size and reroutes the digestive tract, typically resulting in 60–70% excess weight loss. Gastric band places an adjustable band around the stomach to limit food intake; results are more modest (40–50% excess weight loss) and reversal is possible. Gastric sleeve removes about 75% of the stomach, leaving a small pouch; average excess weight loss is 50–60%. Duodenal switch is the most complex procedure, combining stomach reduction with intestinal rerouting, often achieving 70–80% excess weight loss.
All bariatric operations carry surgical risks including infection, bleeding, and blood clots. Long-term complications can include nutritional deficiencies, dumping syndrome, and gallstones. Recovery typically takes 4–6 weeks, though full weight loss takes 18–24 months.
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How It Works
Three simple steps to understand your weight and take action.
Enter your height and weight in our free calculator. Get your BMI, NHS category, healthy weight range, and ethnicity-adjusted thresholds instantly.
If your BMI suggests you're overweight or obese, explore our GLP-1 calculators to project potential weight loss on Mounjaro or Wegovy.
Use our progress tracker to log your weight weekly, visualise your journey with charts, and stay motivated — all stored privately in your browser.
Free Weight Loss Tools & Guides
Everything you need to understand your weight, explore medication options, and track your progress — completely free.
NHS Weight Loss Surgery vs. Non-Surgical Alternatives
Accessing weight loss operations on the NHS requires referral through your GP to a tier 4 specialist bariatric service, with eligibility assessment and typically a waiting period of several months. Private weight loss surgery is available immediately but costs £7,000–£15,000+.
Before surgery is considered, the NHS weight management pathway recommends trying tier 1–3 interventions first: lifestyle support, behaviour change programmes, and prescription weight loss medications like Mounjaro and Wegovy. These prescription options may help you lose 15–20% of body weight without surgical risk. Use our free BMI calculator to assess your current health category, and our GLP-1 weight loss calculator to explore potential results with medical weight loss options before considering surgery.
- Dual GIP/GLP-1 receptor agonist
- Up to 22.5% body weight loss (SURMOUNT-1)
- Weekly injection, dose escalation over 20+ weeks
- Available via private prescription in the UK
- Doses: 2.5mg → 5mg → 7.5mg → 10mg → 12.5mg → 15mg
- GLP-1 receptor agonist
- Up to 15–17% body weight loss (STEP trials)
- Weekly injection, 5-step dose escalation
- NHS & private prescription available
- Doses: 0.25mg → 0.5mg → 1mg → 1.7mg → 2.4mg
Mounjaro vs Wegovy: Head-to-Head
A side-by-side comparison of the two most popular GLP-1 weight loss medications available in the UK.
| Feature | Mounjaro | Wegovy |
|---|---|---|
| Drug class | Dual GIP/GLP-1 agonist | GLP-1 agonist |
| Active ingredient | Tirzepatide | Semaglutide |
| Avg. weight loss | 15–22.5% | 12–17% |
| Key trial | SURMOUNT-1 (2022) | STEP 1 (2021) |
| Max dose | 15 mg weekly | 2.4 mg weekly |
| Escalation period | 20–32 weeks | 16–20 weeks |
| Administration | Weekly injection (pen) | Weekly injection (pen) |
| NHS availability | Private prescription only | NHS & private |
| Approx. private cost | £150–£250/month | £150–£300/month |
| Common side effects | Nausea, diarrhoea, constipation | Nausea, vomiting, diarrhoea |
Data sourced from SURMOUNT-1 and STEP 1 clinical trials. Costs are approximate and vary by provider. Always consult a prescriber.
Am I Eligible for Weight Loss Medication?
In the UK, eligibility for GLP-1 weight loss medications like Mounjaro and Wegovy is based on your BMI and overall health profile.
- BMI of 30 or above (obese)
- Age 18 or over
- No contraindicated conditions
- Committed to lifestyle changes
- BMI of 27 or above
- Plus type 2 diabetes
- Or high blood pressure
- Or obstructive sleep apnoea
Use our BMI calculator to check whether your BMI falls within the eligible range.
How We Built These Tools
Every calculator and guide on myweightcheck is built with accuracy and transparency in mind. Our BMI calculator uses the standard WHO formula with NHS-aligned category thresholds. Our GLP-1 projections are modelled on published clinical trial data from SURMOUNT and STEP studies.
All data stays on your device. We don't require sign-ups, and we don't store your health information on any server. Your progress tracker saves data locally in your browser using localStorage, so only you can see it.
We're based in the UK and our tools are designed specifically for UK users — supporting stone & lbs by default, referencing NHS guidelines, using NICE-approved medication data, and linking to GPhC-registered pharmacies.
Frequently Asked Questions
Common questions about BMI, weight loss medications, and our free UK tools.
What is the difference between weight loss surgery and weight loss injections?
Weight loss surgery (bariatric operations) is invasive and permanent or semi-permanent, typically resulting in 50–80% excess weight loss. Weight loss injections like Mounjaro and Wegovy are prescription medications taken once weekly; they may help achieve 15–clinically studied weight loss. Injections are reversible, have fewer serious complications, and don't require surgery or lengthy recovery.
How much weight can you lose with weight loss operations?
Average excess weight loss ranges from 40–80% depending on the procedure type. A person with a BMI of 45 might lose 30–50 kg over 18–24 months. Results vary based on the specific operation, individual metabolism, and adherence to post-surgery dietary guidelines. Your GP can discuss realistic expectations for your situation.
What are the main risks of bariatric surgery in the UK?
Immediate surgical risks include infection, bleeding, and blood clots. Long-term complications can include nutritional deficiencies (requiring lifelong vitamin supplementation), dumping syndrome, gallstones, and rarely, bowel obstruction. All major surgery carries anaesthetic risk. Discussion with your surgical team is essential before proceeding.
How long is the waiting list for weight loss surgery on the NHS?
NHS waiting times for bariatric surgery vary significantly by region (ICB) and current service capacity. Average wait is 6–18 months from referral to assessment, and a further 3–12 months from approval to surgery. Private surgery can be arranged much more quickly but requires payment of £7,000–£15,000+.
Do you regain weight after weight loss surgery?
Some weight regain is common, typically 5–15% of lost weight within 3–5 years. Long-term success depends on adhering to dietary guidelines, physical activity, and sometimes ongoing medical support. Weight loss medications or additional procedures may be considered if significant regain occurs. Your bariatric team provides ongoing support to minimise regain risk.
Ready to take control of your weight loss journey?
Start with a free BMI check, explore your GLP-1 options, or begin tracking your progress today. No sign-up. No cost. Just results.