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, Fat Loss & Diet — A UK Health Guide
Weight loss and fat loss are often used interchangeably, but they're not quite the same thing. When you lose weight, you're losing fat, muscle, and water — whereas true fat loss focuses on reducing body fat while preserving muscle. This guide explains the difference, covers evidence-based approaches to weight management in the UK, and explores prescription options available to eligible adults. Safe, sustainable weight loss typically involves both dietary changes and increased physical activity, supported by professional guidance from your GP or a weight management specialist.
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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.
Understanding Weight Loss vs Fat Loss
Weight loss refers to a decrease in total body mass, which includes fat, muscle, water, and bone. Fat loss specifically targets excess fat tissue while preserving lean muscle mass. This distinction matters because muscle is metabolically active — losing muscle reduces your resting metabolic rate and makes future weight management harder.
To maximise fat loss rather than general weight loss, combine a moderate calorie deficit (around 500 kcal per day for approximately 0.5 kg per week loss) with resistance exercise to preserve muscle. The NHS recommends losing weight at a rate of 0.5 to 1 kg per week for sustainable results. Crash diets may produce gradual weight management, but much of this is muscle and water — not fat.
- Calculate your personal BMI using our free BMI calculator to establish your starting point
- Track your progress with our free progress tracker to monitor changes over time
- A balanced, reduced-calorie diet alongside strength training optimises fat loss
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 Options Available in the UK
The NHS offers a tiered approach to weight management: tier 1 includes self-help and digital tools, tier 2 involves primary care behaviour change programmes, and tier 3 specialist services may prescribe licensed weight loss medications for eligible adults. Prescription options include GLP-1 receptor agonists like Wegovy (semaglutide) and Mounjaro (tirzepatide), which may help reduce appetite and support weight loss alongside diet and physical activity.
Access varies by region. NHS specialist services have waiting lists, but prescription weight loss medication is also available through private online prescribing following clinical assessment. Our GLP-1 weight loss calculator can help you explore potential outcomes if you're considering medication-supported weight loss. Whatever approach you choose, sustainable weight management works best with professional support from your GP.
- 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 difference between weight loss and fat loss?
Weight loss includes loss of fat, muscle, water, and bone. Fat loss specifically targets fat tissue. Muscle loss can slow your metabolism, making future weight management harder. To prioritise fat loss, use a moderate calorie deficit (around 500 kcal/day) combined with strength training to preserve lean muscle mass.
How quickly should I aim to lose weight?
The NHS recommends losing 0.5 to 1 kg per week for safe, sustainable results. Faster loss (>1.5 kg/week) can result in significant muscle loss and is not recommended without medical supervision. Even modest weight loss of 5–10% of body weight can improve health markers like blood pressure and blood sugar control.
Can prescription weight loss medication help with fat loss?
GLP-1 medications like Wegovy and Mounjaro are prescription-only and may help reduce appetite, supporting weight loss alongside diet and physical activity. Clinical trials showed these medications help participants lose an average of 14–21% of body weight — though individual results vary. They require a prescription following clinical assessment by a licensed prescriber.
What's the most effective diet for weight loss?
Evidence suggests calorie deficit is the most important factor — any diet creating a consistent 500 kcal/day deficit typically produces similar results. Mediterranean, low-carb, and intermittent fasting approaches all work if they help you maintain a deficit. Sustainability matters more than the specific diet type. Your GP can advise on approaches suitable for your health.
How do I access weight loss support on the NHS?
Start by speaking to your GP about weight management support. The NHS offers tier 1 self-help tools and programmes, tier 2 behaviour change services, and tier 3 specialist services where prescription medication may be available. Availability varies by region and ICB. Your GP can refer you to local services and discuss medication eligibility if appropriate.
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.