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
Free tracker included with every download this week
Weight Loss For Surgery — Why It Matters
If you're facing surgery, your GP or surgical team may recommend losing weight beforehand to improve your health outcomes and reduce surgical risks. Weight loss before surgery can lower the chance of complications, reduce anaesthetic risks, and support faster recovery. The NHS provides support through multiple pathways, including lifestyle changes, weight management programmes, and in some cases, prescription weight loss medication. Understanding your options helps you prepare effectively for your procedure.
10,000+ calculations today · NHS-aligned thresholds · 100% free
Calculate Your BMI Instantly
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.
Why Weight Loss Before Surgery Is Important
Pre-operative weight loss reduces several surgical risks:
- Lower infection rates post-surgery
- Reduced anaesthetic complications
- Improved wound healing
- Shorter recovery time and hospital stays
- Better long-term surgical outcomes
Even modest weight loss of 5–10% of your body weight can make a meaningful difference. Your surgical team will assess your individual case and set realistic weight loss targets based on your procedure type, current health, and timeline. Use our free BMI calculator above to understand your current weight status, then work with your GP to create a personalised weight loss plan suited to your surgery date and health needs.
Clinically BackedWeight Loss
No appointments. No waiting rooms. Just care — from a UK-regulated online pharmacy.
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 Support And Prescription Options
The NHS offers weight management support through multiple tiers. Your GP can refer you to local weight management programmes combining diet, physical activity, and behaviour change support. For eligible adults, prescription weight loss medication may be available through specialist NHS services, though waiting lists vary significantly by region. Prescription weight loss UK options include GLP-1 medications like semaglutide (Wegovy), which clinical trials showed helps people lose an average of 15% body weight alongside dietary changes. Our GLP-1 weight loss calculator can help you understand potential results, though individual outcomes vary. Your surgical team and GP will advise which approach suits your timeline and health profile best.
- 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.
How much weight should I lose before surgery?
This depends on your procedure, current BMI, and health profile. Your surgical team will set a personalised target. Generally, losing 5–10% of body weight significantly reduces surgical risks. Discuss realistic timelines with your GP — gradual weight management can be risky without medical supervision.
How long before surgery should I start losing weight?
Ideally, begin 2–3 months before your procedure if possible. This allows sustainable, safe weight loss and time for your body to adjust. If your surgery is sooner, your GP can advise on safe approaches. Never attempt very gradual weight management without medical guidance.
Can I use weight loss injections before surgery?
GLP-1 medications like Wegovy are prescription-only and require clinical assessment. If eligible, they may help — but your surgical team must know about any medications you're taking. Discuss this with both your GP and your surgeon, as they need to coordinate your care safely.
What's the safest way to lose weight before surgery?
A combination of moderate calorie reduction (500 kcal/day deficit) and increased physical activity is safest. Avoid very low-calorie diets without medical supervision. Your GP or a specialist weight management service can create a safe, personalised plan suited to your surgery timeline.
Will weight loss help my recovery after surgery?
Yes. Lower pre-operative weight improves wound healing, reduces infection risk, and often shortens hospital stays. It also supports better long-term outcomes. Even modest weight loss before surgery has measurable benefits for recovery and post-operative health.
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.