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 Measure Weight Loss Percentage
Measuring weight loss as a percentage of your starting weight is more meaningful than looking at kilograms alone—it shows real progress regardless of your starting point. Whether you're managing weight through lifestyle changes, NHS weight loss programmes, or prescription weight loss medication, understanding your percentage loss helps you track meaningful health improvements. Here's how to calculate it accurately and why it matters for your weight management UK journey.
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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
Weight loss percentage is calculated using a simple formula: divide the amount of weight lost by your starting weight, then multiply by 100.
- Formula: (Starting weight − Current weight) ÷ Starting weight × 100 = Weight loss %
- Example: If you weigh 100 kg at the start and now weigh 90 kg, you've lost 10 kg. (10 ÷ 100) × 100 = clinically studied weight loss
- Why this matters: A 10 kg loss means different things for a 70 kg person versus a 130 kg person. As a percentage, it shows true progress. The NHS and clinical trials (including Wegovy STEP trials and Mounjaro studies) report weight loss as a percentage because it's the most honest measure of progress
- Using the weight converter: If you work in stone and pounds, convert to kg first, then calculate. Our free weight converter makes this easy—simply enter your starting and current weights in any unit
Most healthcare professionals recommend aiming for 5–clinically studied weight loss as an initial realistic goal—research shows this level of loss significantly improves blood pressure, blood sugar control, and cardiovascular health.
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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.
Tracking Your Progress Effectively
Measuring weight loss percentage helps you see progress even when the scales seem stuck. Weigh yourself weekly at the same time (ideally morning, after toilet, before eating) and record both the absolute weight and your running percentage loss. Use our free progress tracker to log your weight automatically and watch your percentage improve over time.
If you're using prescription weight loss medication like Mounjaro or Wegovy, or following an NHS weight loss programme, think in terms of milestones: 5%, 10%, 15%, 20%. Clinical trials show average losses of 15–21% with prescription medications—but individual results vary significantly and are achieved alongside a reduced-calorie diet and increased physical activity. Your GP can help you set realistic targets based on your personal health context.
- 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 realistic weight loss percentage per month?
The NHS recommends losing 0.5–1 kg per week, which is approximately 2–4 kg (2–4%) per month depending on your starting weight. This rate is sustainable and helps preserve muscle. Faster loss may occur initially but often isn't maintained. Always consult your GP if you're considering gradual weight management programmes.
Why do clinical trials report weight loss as a percentage?
Percentage loss is the fairest way to compare results across people of different sizes. Someone losing 15 kg from 100 kg (15% loss) has achieved the same proportional progress as someone losing 12 kg from 80 kg (15% loss)—even though the absolute numbers differ. Wegovy and Mounjaro trials use percentages for this reason.
How does weight loss percentage relate to BMI improvement?
As you lose weight (expressed as a percentage), your BMI automatically decreases. Use our free BMI calculator to see how your BMI changes as your percentage loss grows. A clinically studied weight loss often moves people into a lower BMI category, which is clinically significant for health outcomes.
Should I measure weight loss percentage or absolute weight loss?
Both are useful. Absolute weight (in kg) shows you're moving the scales; percentage shows meaningful progress relative to your starting point. Track both—percentage is better for motivation and comparing to clinical trial data, while absolute weight helps with practical goals like fitting into specific clothes sizes.
Can I calculate weight loss percentage if I use stone and pounds?
Yes. Convert stone and pounds to kg first (our free weight converter does this instantly), then apply the formula. If you started at 100 kg and now weigh 90 kg, that's 10% loss whether you're tracking in stone, pounds, or kilograms—the percentage is the same across all units.
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.