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 Do You Figure Out Percentage of Weight Loss?
Working out your weight loss percentage is straightforward: divide the amount you've lost by your starting weight, then multiply by 100. This percentage matters more than absolute kilograms because it shows your true progress relative to your body size. NHS guidance uses percentage weight loss to measure treatment success, and prescription weight management medications are assessed the same way. Whether you're tracking progress yourself or considering prescription options available in the UK, understanding your percentage loss helps you see real results.
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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.
The Weight Loss Percentage Formula
The calculation is simple: divide weight lost by starting weight, then multiply by 100. For example, if you started at 90kg and now weigh 80kg, you've lost 10kg. Divide 10 by 90 = 0.111, then multiply by 100 = clinically studied weight loss.
- Starting weight: your weight when you began tracking
- Current weight: your weight now
- Weight lost: starting weight minus current weight
- Percentage: (weight lost ÷ starting weight) × 100
Use our free weight converter above to switch between kg, stone, and lbs if needed. Even a 5–10% reduction produces meaningful health improvements according to NHS evidence. Clinical trials of prescription weight loss medication like Mounjaro and Wegovy measure success as percentage weight loss, typically ranging from 15% to 20% over 12–16 weeks. Our GLP-1 weight loss calculator can help you estimate potential percentage loss at different doses.
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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.
Weight Loss Medications and Percentage Results in the UK
If you're exploring weight management in the UK, prescription options are available through NHS specialist services or private assessment. Mounjaro (tirzepatide) helped participants lose an average of 15–21% of body weight in clinical trials, while Wegovy (semaglutide) achieved approximately 15% average loss. Eligibility includes adults with a BMI of 30 or above, or 27 or above with weight-related health conditions like type 2 diabetes or high blood pressure.
Your GP can assess whether prescription weight loss medication is suitable for you. These are always used alongside reduced-calorie diet and increased physical activity — medication supports these changes rather than replacing them. Track your percentage loss over time using our free progress tracker to see how your results compare to NHS and clinical benchmarks.
- 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's a healthy rate of weight loss percentage per week?
The NHS recommends losing 0.5–1kg (approximately 0.5–1% of body weight) per week for sustainable results. Faster loss is possible with medical support but increases muscle loss risk. Individual results vary based on starting weight, metabolism, and lifestyle changes.
Why is percentage weight loss better than just looking at kilograms?
Percentage weight loss accounts for your body size. Losing 10kg means different things if you weigh 80kg versus 150kg. A 10% loss from 100kg is more significant and healthier than a 10kg loss from 150kg, which is only 6.7%. Percentage shows real progress relative to your starting point.
Can I calculate weight loss percentage using stone and pounds?
Yes. Convert your starting weight and current weight to the same unit using our weight converter, then apply the formula. For example, if you've gone from 12 stone to 11 stone, that's 14lbs lost. Divide 14 by 168lbs (12 stone) = 8.3% loss. UK measurements work the same way.
Do prescription weight loss medications in the UK assures a specific percentage loss?
No. Clinical trials showed average results, but individual responses vary significantly. Mounjaro and Wegovy achieve best results when combined with dietary changes and physical activity. Your prescriber will monitor your progress and adjust treatment based on your personal response.
How does my BMI relate to weight loss percentage?
Weight loss percentage and BMI are related but separate. You can calculate both using our free BMI calculator and weight converter above. A clinically studied weight loss typically lowers BMI by 3–4 points. Checking both measurements gives a complete picture of your progress and health improvement. ```
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.