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
What Is Safe Weight Loss?
Safe weight loss means losing weight at a sustainable pace whilst protecting your health and muscle mass. The NHS recommends losing no more than 0.5 to 1 kg (1 to 2 lbs) per week for most adults. This pace may seem modest, but it's designed to help you keep the weight off long-term and reduce the risk of nutritional deficiencies, fatigue, and muscle loss. Your GP can advise you on what's safe for your individual circumstances, especially if you have existing health conditions.
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.
Healthy Weight Loss Rates and Methods
The NHS safe weight loss target is 0.5 to 1 kg per week. This typically requires a calorie deficit of around 500 kcal per day, which means eating approximately 500 calories fewer than your body needs. Faster weight loss is possible under medical supervision, but it increases the risk of losing muscle mass, nutrient deficiencies, and gallstones.
For sustainable weight management in the UK, most people benefit from combining dietary changes with increased physical activity. Even a 5% reduction in body weight can significantly improve blood pressure, blood sugar control, and reduce joint strain. Crash diets and extreme calorie restriction (under 800 kcal per day) should only be undertaken under close medical supervision.
- Aim for steady, predictable progress — 2 to 4 kg per month is realistic
- Include protein and fibre to maintain muscle and feel fuller longer
- Stay hydrated and monitor energy levels closely
- Track your progress using our free progress tracker to stay motivated and spot patterns
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.
When to Consider Medical Support for Weight Loss
If you've tried lifestyle changes alone without significant progress, or if you have weight-related health conditions like type 2 diabetes, high blood pressure, or sleep apnoea, your GP may suggest additional support. The NHS offers tier 1 and tier 2 weight management services, and specialist tier 3 services in some areas where prescription weight loss medication—including GLP-1 medications like Wegovy—may be considered.
Prescription weight loss medications may help with weight management UK when used alongside diet and exercise. Check your BMI using our free BMI calculator to understand your starting point, and discuss options with your GP. Access to these treatments varies by region, and a clinical assessment is always required before prescription.
- 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.
How much weight should I aim to lose per week safely?
The NHS recommends losing 0.5 to 1 kg (1 to 2 lbs) per week. This requires a calorie deficit of roughly 500 kcal daily. Faster loss can lead to muscle loss and nutritional problems, so steady progress is safer and more sustainable long-term.
What's the difference between safe weight loss and crash dieting?
Safe weight loss is gradual (0.5–1 kg/week) and includes balanced nutrition. Crash diets cut calories extremely (often under 800 kcal/day) and cause rapid loss, muscle damage, nutrient deficiencies, and usually regain. Only very low-calorie diets should be done under medical supervision.
Can I lose weight faster with prescription medication?
Some prescription weight loss medications may help alongside lifestyle changes, but they're not a shortcut. Clinical trials show GLP-1 medications support modest weight loss over months. They still require a reduced-calorie diet and physical activity—medication enhances, not replaces, healthy habits.
What should I include in a safe weight loss plan?
A safe plan combines a modest calorie deficit (500 kcal/day), adequate protein and fibre, regular physical activity, and consistent sleep and stress management. Track your progress using available tools to monitor what works. Your GP or a weight management service can personalise this for you.
How do I know if my weight loss is healthy?
Healthy weight loss should feel sustainable—you shouldn't feel constantly exhausted, dizzy, or unwell. You should lose fat without severe muscle loss. If you experience unusual fatigue, hair loss, or other concerning symptoms, contact your GP immediately.
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.