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
Weight Loss Calculator — Estimate Your Potential
A weight loss calculator helps you understand realistic weight loss projections based on your current weight, goals, and the method you're using. Whether you're considering prescription weight loss medication like GLP-1 injections, following a calorie-controlled diet, or combining lifestyle changes with medication, calculating your potential weight loss gives you a practical roadmap. The NHS recommends losing 0.5–1 kg per week for sustainable results. Our free tools help you project outcomes and track your progress 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.
How Weight Loss Calculations Work
Weight loss calculations are based on calorie deficit — the difference between calories consumed and calories burned. The NHS advises a deficit of approximately 500 kcal per day to achieve 0.5 kg weekly loss, or 1,000 kcal per day for 1 kg per week (though faster loss should only be pursued under medical guidance).
For GLP-1 weight loss medication like Wegovy or Mounjaro, weight loss projections are based on clinical trial data. In the STEP-1 trial, Wegovy users lost an average of around 15% of their body weight over 68 weeks. Mounjaro users in the SURMOUNT-1 trial achieved average losses of 15–21% depending on dose. However, individual results vary significantly.
Our GLP-1 weight loss calculator estimates potential outcomes at different doses, combined with dietary changes and increased physical activity — the evidence-based approach used in clinical trials.
- Calorie deficit method: 500 kcal/day = ~0.5 kg/week loss
- GLP-1 medication: average 15–clinically studied weight loss over 68+ weeks
- Combined approach: medication plus lifestyle changes yields best results
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 Management in the UK
The NHS describes weight management through a tiered approach. Tier 1 includes self-help resources and community programmes. Tier 2 involves GP-led behaviour change interventions. Tier 3 specialist services — available through NHS referral — offer prescription weight loss medication alongside dietary and lifestyle support.
Prescription weight loss options in the UK include Wegovy (semaglutide), Mounjaro (tirzepatide), and Saxenda (liraglutide). All are prescription-only and require clinical assessment to check eligibility. Access through the NHS varies significantly by region, with waiting lists in many areas. Private prescribing through GPhC-registered online services offers faster access without NHS referral.
To check your starting point, use our free BMI calculator to see whether you fall into the overweight or obese category. You can then discuss weight loss options with your GP or a licensed prescriber.
- 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 projection?
The NHS recommends losing 0.5–1 kg per week through calorie deficit and lifestyle change. With GLP-1 medication, clinical trials show average losses of 15–21% of body weight over 68+ weeks. Individual results vary based on starting weight, adherence, diet, and exercise. Use our free weight loss calculator to estimate realistic outcomes for your specific situation.
How does a calorie deficit create weight loss?
Weight loss occurs when you consume fewer calories than your body burns. A 500 kcal daily deficit typically results in 0.5 kg weekly loss; 1,000 kcal deficit can yield 1 kg per week. The NHS advises sustainable deficits rather than very rapid loss to preserve muscle mass and support long-term success. Our progress tracker helps you monitor weekly changes.
Do GLP-1 injections clinically studied weight loss?
No medication assures weight loss. GLP-1 injections like Wegovy and Mounjaro are prescription-only and support weight loss alongside dietary changes and physical activity — they're not replacements for lifestyle changes. Clinical trials show average weight loss, but individual results vary. A prescriber assesses whether the medication is suitable for you based on your health.
How do I access weight loss medication in the UK?
NHS access is through specialist tier 3 weight management services — your GP can refer you, though waiting lists vary by region. Private access is available through GPhC-registered online prescribers following a clinical assessment. Both routes require eligibility checks based on BMI and health conditions. Use our BMI calculator to check your starting point.
What's the difference between Wegovy and Mounjaro?
Both are once-weekly injections licensed for UK weight loss. Wegovy (semaglutide) is a GLP-1 agonist; Mounjaro (tirzepatide) is a dual GIP/GLP-1 agonist. Clinical trials show similar average weight loss ranges (15–21%), though Mounjaro's dual mechanism may offer slightly different results. Individual outcomes vary, and a prescriber advises which suits you best.
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.