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 to lose weight quickly — safely and sustainably
Losing weight quickly is a common goal, but the NHS recommends a sustainable approach to weight management rather than crash dieting. While gradual weight management can feel motivating, losing weight too fast often leads to muscle loss, nutritional deficiencies, and weight regain. This UK health guide explains safe weight loss rates, when quick weight loss is medically appropriate, and how to use your BMI calculator and weight converter to track progress effectively.
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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.
NHS guidance on safe weight loss rates in the UK
The NHS recommends losing weight at a rate of 0.5 to 1 kg (1 to 2 lbs) per week for sustainable results. This typically requires a calorie deficit of around 500 kcal per day, which can be achieved through a combination of reduced food intake and increased physical activity. Faster weight loss — more than 1.5 kg per week — is not recommended without medical supervision because it significantly increases the risk of losing muscle tissue, gallstones, dehydration, and nutrient deficiencies.
However, very gradual weight management (800 kcal per day or less) may be medically appropriate in specific circumstances, such as preparation for bariatric surgery or managing acute health complications. These very low-calorie diets (VLCDs) are only safe under close medical supervision from your GP or a specialist weight management service. UK NICE guidelines emphasise that any weight loss programme should focus on long-term behaviour change, not short-term rapid results.
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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.
Quick weight loss methods available in the UK
Several approaches can support faster weight loss when medically appropriate. Prescription weight loss injections, such as Mounjaro or Wegovy, can help alongside reduced-calorie diet and exercise — clinical trials showed average weight loss of 15–21% over several months. NHS specialist weight management services may recommend structured low-calorie diets for selected patients. Intermittent fasting (16:8 or 5:2) and specific diet plans like the Mediterranean approach have evidence for modest weight loss. Always discuss any gradual weight management strategy with your GP first, especially if you have existing health conditions or take medications. Use our free BMI calculator to track where you stand and monitor progress safely.
- 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.
Is losing 2 kg per week safe?
The NHS recommends 0.5–1 kg per week as safe and sustainable. Losing 2 kg weekly is very rapid and increases risks of muscle loss, nutrient deficiencies, and gallstones. Only attempt with medical supervision. Always consult your GP before attempting gradual weight management.
What is a very low-calorie diet (VLCD)?
A VLCD provides under 800 kcal daily. These are only safe under medical supervision from a GP or specialist weight management service. They're sometimes used before bariatric surgery or for acute health reasons. VLCDs are not recommended for self-directed weight loss.
Can prescription weight loss injections cause gradual weight management?
Yes. Mounjaro and Wegovy are GLP-1 medications that, alongside a reduced-calorie diet, can support faster weight loss than diet alone — averaging 15–clinically studied weight loss. They require a prescription and clinical assessment. Individual results vary significantly.
How does calorie deficit relate to weight loss speed?
A 500 kcal daily deficit typically results in losing 0.5 kg weekly. A 1,000 kcal deficit supports losing 1 kg weekly. Larger deficits create faster loss but increase health risks. Your GP can advise on a safe deficit for your circumstances.
What happens after gradual weight management?
gradual weight management often leads to weight regain — a problem called "rebound weight gain" — because unsustainable eating patterns resume. The NHS recommends sustainable lifestyle changes for lasting weight management. A progress tracker can help monitor long-term trends.
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.