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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Weight Loss Percentage Calculator — UK Guide
Working out your weight loss percentage helps you track real progress beyond the number on the scales. A weight loss percentage calculator shows how much of your starting weight you've actually lost, which is more meaningful than absolute weight alone. Whether you're managing weight through lifestyle changes, NHS weight management programmes, or prescription weight loss medication like GLP-1 injections, understanding your percentage loss keeps you motivated. This guide explains how to calculate it, what the numbers mean, and how to use our free tools to monitor your journey.
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.
How to Calculate Your Weight Loss Percentage
Weight loss percentage is calculated using this simple formula: (Starting weight – Current weight) ÷ Starting weight × 100 = Weight loss percentage
For example, if you started at 100kg and now weigh 90kg, your calculation is: (100 – 90) ÷ 100 × 100 = clinically studied weight loss.
This percentage-based approach is particularly useful in UK weight management programmes because it accounts for your individual starting point. Someone losing 5kg might represent a 10% loss for one person but only a 5% loss for another. The NHS recognises that a 5–10% reduction in body weight can deliver meaningful health benefits, including improved blood sugar control, lower blood pressure, and reduced joint strain. Use our free progress tracker to log your weight regularly and automatically calculate your percentage loss over time. You can also use our weight converter to track progress across different units (kg, stone, lbs).
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.
Weight Loss Percentage and Health Outcomes
Research shows that even modest weight loss percentages deliver real health improvements. Losing just 5% of your body weight can reduce type 2 diabetes risk and improve cardiovascular markers. At clinically studied weight loss, many people report better energy, improved mobility, and reduced sleep apnoea symptoms. Clinical trials of GLP-1 weight loss medications show average losses of 14–21% body weight, though individual results vary significantly.
Your weight loss percentage matters more than the absolute number because it reflects your personal effort and health gain. Two people losing 10kg have achieved the same absolute loss, but their percentage achievements differ if one started at 70kg and the other at 120kg. Track your percentage alongside your BMI using our free BMI calculator to see how your health markers improve as you progress.
- 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 month?
The NHS recommends losing 0.5–1kg per week, which is roughly 2–4kg per month. This typically equals 5–clinically studied weight loss over 3 months, depending on your starting weight. Faster losses are possible with medical support but may increase muscle loss. Aim for sustainable, steady progress rather than rapid loss.
Can I use a weight loss percentage calculator with prescription weight loss medication?
Yes. Medications like Mounjaro and Wegovy are used alongside reduced-calorie diets and exercise. Tracking your weight loss percentage helps monitor whether the medication is supporting your progress effectively. Always use your percentage calculator in addition to regular GP check-ins — your prescriber will assess your response individually.
How does weight loss percentage relate to BMI?
Your weight loss percentage and BMI are connected but different. A clinically studied weight loss always reduces your absolute weight, but how much your BMI falls depends on your height. Use our free BMI calculator to see how your BMI category changes as your weight loss percentage increases — this shows your actual health progress.
Is clinically studied weight loss considered significant?
Yes. A clinically studied weight loss is substantial and typically indicates meaningful health improvements across multiple markers. Clinical trials of GLP-1 weight loss medications show some participants achieve 20–21% losses, though results vary. This level of loss usually improves blood pressure, blood sugar, cholesterol, and joint function.
What's the best way to track weight loss percentage over time?
Log your weight weekly at the same time of day (ideally morning before eating). Our free progress tracker automatically calculates your percentage loss from your starting weight. Avoid daily weighting — weight fluctuates due to water retention, meals, and hormones. Weekly tracking gives a clearer picture of your true trend.
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.