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
How to Calculate Weight Loss Percentage
Calculating your weight loss percentage helps you track progress beyond just the numbers on the scales. To work out your percentage, subtract your current weight from your starting weight, divide by your starting weight, then multiply by 100. For adults in the UK managing their weight, understanding this calculation is useful alongside other metrics like BMI and waist measurements. If you're considering prescription weight management UK options, calculating your baseline weight loss percentage can help you and your GP assess effectiveness of any treatment plan over time.
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.
UK Prescription Weight Management Options
Three prescription-only medications are licensed in the UK for weight management, all requiring clinical assessment before prescription:
- Mounjaro (tirzepatide) — Dual GIP and GLP-1 agonist, once-weekly injection. Clinical trials showed average weight loss of 15–21% body weight at maximum dose alongside reduced-calorie diet and exercise.
- Wegovy (semaglutide) — GLP-1 agonist, once-weekly injection. Average weight loss approximately 15% body weight in clinical trials at 2.4mg dose.
- Saxenda (liraglutide) — GLP-1 agonist, once-daily injection. Similar effectiveness to Wegovy with slightly different dosing schedule.
Eligibility typically requires BMI of 30 or above, or 27+ with weight-related health conditions like type 2 diabetes, high blood pressure, or sleep apnoea. Individual results vary significantly. Weight loss injections work alongside dietary and lifestyle changes, not instead of them. Use our GLP-1 weight loss calculator to estimate potential weight loss percentage at different doses based on clinical trial data.
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 vs Private Access in the UK
NHS access is through specialist tier 3 weight management services — you'll need a referral from your GP. Availability and waiting times vary significantly by region (ICB). Many areas have substantial waiting lists; some have limited access. Private access is available through GPhC-registered online pharmacies following an online clinical assessment with a UK-licensed prescriber — no NHS referral needed, though costs typically range from £129–£320 monthly depending on dose.
Start by discussing weight management UK options with your GP. They can assess whether you're eligible, refer you to NHS specialist services if appropriate, or advise on private options. Use our BMI calculator to determine your current BMI category — this helps frame the conversation with your healthcare provider about what weight loss percentage might be realistic and healthier for you.
- 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 a healthy weight loss percentage per month?
NHS guidance recommends losing 0.5–1kg (1–2lbs) per week, which equals roughly 2–4kg per month or 4–8% monthly loss depending on starting weight. This sustainable rate reduces muscle loss and improves long-term success. Faster loss is possible with medical support but requires professional supervision.
Can I calculate weight loss percentage if I'm using Mounjaro or Wegovy?
Yes. Record your starting weight, then calculate percentage monthly or quarterly. Clinical trial data shows average weight loss of 15–21% with Mounjaro and 15% with Wegovy, but individual results vary. Track your progress using our free progress tracker alongside percentage calculations.
How does weight loss percentage relate to BMI improvement?
Weight loss percentage directly lowers your BMI. Losing 10% of body weight typically reduces BMI by approximately 2.5–3 points. Use our BMI calculator to see how your current weight translates to BMI, then recalculate as you lose weight to monitor progress toward the healthy range of 18.5–24.9.
Why calculate weight loss percentage rather than just kilograms?
Percentage is more meaningful because a 10kg loss for someone weighing 120kg is different from 10kg for someone weighing 70kg. Percentage accounts for your starting point, making it easier to compare progress fairly and set realistic goals for nhs weight loss or prescription medication outcomes.
Should I aim for a specific weight loss percentage with prescription medication?
Clinical averages range from 15–21% depending on the medication and dose, but your individual result depends on your adherence, diet, exercise, genetics, and overall health. Discuss realistic targets with your prescriber rather than aiming for clinical trial averages. Even modest weight loss (5–10%) delivers significant health benefits.
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.