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
Fast Weight Loss Diet — What the NHS Recommends
If you're looking to lose weight quickly, it's important to understand what's safe and sustainable according to UK health guidance. The NHS recommends losing weight at a rate of 0.5 to 1 kg per week for best results, though some people can achieve faster loss under medical supervision. This guide covers NHS-aligned approaches to weight loss, realistic expectations, and how to support your goals safely. Remember, healthy weight management involves both dietary changes and lifestyle adjustments — quick fixes rarely lead to lasting results.
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.
NHS Guidance on Safe and Fast Weight Loss
The NHS recommends weight loss of 0.5 to 1 kg per week as the safest, most sustainable approach. This rate comes from a calorie deficit of approximately 500 to 1,000 calories per day, achieved through diet and exercise combined.
Faster weight loss is possible but requires medical support:
- Low calorie diets (1,200–1,500 kcal/day) — should only be followed with GP guidance and regular monitoring
- Very low calorie diets (under 800 kcal/day) — only under specialist supervision, typically in NHS tier 3 weight management services
- Prescription weight loss medications — including GLP-1 injections like Mounjaro and Wegovy, prescribed through specialist services or private consultation following clinical assessment
Faster loss increases the risk of muscle loss, nutritional deficiency, gallstones, and weight regain. Individual circumstances vary, so speak with your GP before starting any gradual weight management programme.
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.
UK Tools and Resources to Support Your Weight Management
To track your progress safely, use our free BMI calculator to establish your current health baseline — this helps your GP assess whether faster weight loss is appropriate for you. Our weight converter makes it easy to understand your weight in both metric and imperial measurements, essential for following NHS guidance accurately.
For those considering GLP-1 weight loss medications available in the UK, our GLP-1 weight loss calculator can help you understand potential outcomes at different doses. Use our free progress tracker to log weekly weight, dietary changes, and activity levels — tracking is proven to improve adherence and results. Always discuss any gradual weight management plan with your GP first, especially if you have existing health conditions.
- 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 it safe to lose weight very quickly in the UK?
The NHS recommends losing 0.5 to 1 kg per week as the safest approach. Faster loss (more than 1.5 kg/week) increases risks of muscle loss, gallstones, and nutritional deficiency. Very rapid loss should only be attempted under medical supervision through NHS specialist services or with direct GP guidance.
What's the fastest safe diet approach in the UK?
A calorie deficit of around 500–1,000 kcal per day (achieved through diet and exercise) typically results in 0.5 to 1 kg loss per week. Low calorie diets (1,200–1,500 kcal) can accelerate loss but require GP monitoring. Prescription medications like GLP-1 injections offer faster results with medical support.
Should I use a very low calorie diet (VLCD) for fast weight loss?
VLCDs (under 800 kcal/day) are only safe under medical supervision, typically through NHS tier 3 specialist weight management services. They carry risks including nutrient deficiency, muscle loss, and metabolic adaptation. Always consult your GP before considering a VLCD.
Can prescription weight loss injections help me lose weight faster?
Yes. GLP-1 medications like Mounjaro and Wegovy are available in the UK through NHS specialist services or private prescription following clinical assessment. Clinical trials show average weight loss of 15–21% of body weight over 68 weeks. Results vary individually and work best alongside dietary changes and increased activity.
How do I know if fast weight loss is right for me?
Speak with your GP first. They can assess your BMI, health conditions, and medications to determine if accelerated weight loss is appropriate. Use our free BMI calculator to establish your baseline, then discuss your goals and the fastest safe approach with your healthcare professional. ```
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.