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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How to Calculate Weight Loss Percentage
Calculating your weight loss percentage is a practical way to track progress beyond the scales. Rather than focusing on kilograms alone, expressing weight loss as a percentage of your starting weight gives a clearer picture of your achievement. For adults in the UK considering prescription weight loss medication as part of their management strategy, understanding this calculation helps you assess realistic expectations alongside NHS weight management guidance.
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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.
UK Prescription Weight Loss Options and Eligibility
Three prescription-only medications are currently licensed in the UK for weight management alongside diet and exercise:
- Mounjaro (tirzepatide) — a once-weekly injection using dual GIP and GLP-1 technology. Clinical trials showed average weight loss of 15–21% of body weight over 72 weeks.
- Wegovy (semaglutide) — a once-weekly GLP-1 injection. Evidence suggests average weight loss of around 15% of body weight.
- Saxenda (liraglutide) — a daily GLP-1 injection for weight management.
You may be eligible if you have a BMI of 30 or above, or BMI 27–29.9 with weight-related health conditions such as type 2 diabetes, prediabetes, high blood pressure, or cardiovascular disease. Eligibility varies by ethnicity — lower thresholds apply for South Asian, Chinese, Black African, and Black Caribbean adults due to higher health risks at lower BMI levels. Try our free BMI calculator to check your starting point, then use our GLP-1 weight loss calculator to explore potential outcomes at different doses.
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 Access vs Private Routes in the UK
In the UK, prescription weight loss medication is available through two routes. NHS access is via specialist tier 3 or 4 weight management services — typically requiring referral from your GP and involving waiting lists that vary significantly by region. Private access is available through GPhC-registered online pharmacies following a consultation with a UK-licensed prescriber, without NHS referral.
If you're interested in exploring medication-supported weight loss, speak to your GP about your options. They can assess your individual health and discuss whether prescription medication is appropriate for you. Recording your starting weight and calculating your progress percentage — using our free progress tracker — helps demonstrate the effectiveness of any approach you choose alongside lifestyle changes.
- 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 do I calculate my weight loss percentage?
Divide the weight you've lost by your starting weight, then multiply by 100. Example: if you started at 100kg and lost 15kg, your percentage loss is (15 ÷ 100) × 100 = 15%. This percentage-based measure is more meaningful than absolute weight because it reflects your individual progress, especially when comparing results across different body sizes.
What weight loss percentage should I expect with prescription medication?
Clinical trial data shows that Mounjaro helps achieve average weight loss of 15–21% of body weight, while Wegovy shows average losses around 15%. However, individual results vary significantly based on dose, adherence, and lifestyle factors. Use our GLP-1 weight loss calculator to see projected ranges for your situation.
How quickly should I see weight loss results?
The NHS recommends losing weight at a safe rate of 0.5–1kg per week. With prescription GLP-1 medication, some weight loss may appear within the first few weeks, but meaningful results typically become evident after 8–12 weeks. Consistency with both medication and lifestyle changes matters most.
What's the difference between NHS and private weight loss medication access in the UK?
NHS access is through specialist weight management services (often with waiting lists) following GP referral. Private access is through online prescribers and GPhC-registered pharmacies without NHS referral but at personal cost. Both require clinical assessment — neither provides medication without a proper prescription and health review.
Can I use weight loss percentage to decide if medication is working?
Yes, tracking weight loss percentage helps you assess progress objectively. A loss of 5% of body weight produces measurable health benefits. Recording your starting weight and regular measurements using our free progress tracker lets you monitor your percentage loss alongside other health improvements like blood pressure or energy levels.
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.