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
Best Fast Weight Loss Diet — What Works in the UK
There's no single "best" fast weight loss diet, but evidence-based approaches combined with medical support can deliver meaningful results. In the UK, the NHS recommends losing weight at a rate of 0.5 to 1 kg per week for sustainable, healthy outcomes. While gradual weight management is possible with prescription medication and strict calorie restriction, the fastest approach often involves combining dietary changes with professional guidance. Our free BMI calculator helps you understand your current health status, and for those eligible, prescription weight loss medication may accelerate progress alongside lifestyle changes.
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.
Evidence-Based Fast Weight Loss Methods
The fastest safe weight loss combines several approaches: calorie deficit (aim for 500–750 kcal daily deficit for 0.5–1 kg per week), structured diet (low-carb, Mediterranean, or intermittent fasting show evidence for rapid initial loss), and increased physical activity (both resistance training to preserve muscle and cardiovascular exercise). For those meeting NHS eligibility criteria, prescription weight loss medication may accelerate results—Mounjaro and Wegovy are GLP-1 receptor agonists that reduce appetite and support sustainable weight loss alongside lifestyle changes. NICE recommends medication as part of specialist weight management programmes for adults with BMI ≥30 or ≥27 with weight-related health conditions. Try our GLP-1 weight loss calculator to estimate potential results at different doses if you're considering medication options.
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.
NHS Weight Loss Pathway and Realistic Timescales
The NHS weight management pathway has four tiers: tier 1 (self-help and community programmes), tier 2 (primary care-based behaviour change), tier 3 (specialist multidisciplinary services where prescription medication may be offered), and tier 4 (bariatric surgery for severe obesity). Realistic timescales: with a 500 kcal daily deficit, expect 2 kg monthly loss; with prescription medication alongside reduced-calorie diet, clinical trials show 15–clinically studied weight loss over 68 weeks. Fast weight loss is possible, but sustainable results come from combining dietary changes with professional support. Your GP can refer you to specialist services, or you can access private prescribing following an online clinical assessment.
- 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 the fastest safe rate to lose weight?
The NHS recommends 0.5–1 kg per week as the safest, most sustainable rate. Faster loss (>1.5 kg weekly) requires medical supervision and increases risk of muscle loss, nutrient deficiency, and gallstones. Combined dietary change and physical activity work best.
Can prescription weight loss injections like Mounjaro speed up weight loss?
Yes. Mounjaro (tirzepatide) and Wegovy (semaglutide) are GLP-1 receptor agonists that may help you lose 15–21% of body weight when combined with a reduced-calorie diet and exercise. Results vary significantly between individuals. Both are prescription-only and require clinical assessment.
Which diet produces the fastest weight loss results?
Low-calorie diets, intermittent fasting, and low-carb approaches show rapid initial weight loss, particularly in the first 4 weeks. However, Mediterranean and moderate calorie-deficit diets show better long-term sustainability. The "best" diet is one you can stick to alongside physical activity.
Is fast weight loss safe for my health?
Losing 0.5–1 kg weekly is safe and recommended by the NHS. Faster loss may cause muscle loss, nutritional deficiencies, dehydration, and gallbladder problems. Always consult your GP before starting gradual weight management, especially if you have existing health conditions.
How can I track my weight loss progress?
Use our free progress tracker on this page to log your weight weekly and see trends over time. Also use our BMI calculator and weight converter to monitor changes in your BMI category and health status as you progress.
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.