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 Normal Weekly Weight Loss?
The NHS recommends losing weight at a rate of 0.5 to 1 kg (approximately 1 to 2 lbs) per week for sustainable, long-term results. This moderate pace helps preserve muscle mass, supports behavioural change, and is more likely to be maintained than gradual weight management. Losing more than 1.5 kg per week without medical supervision is not advisable, as it increases the risk of nutritional deficiencies, muscle loss, and gallstones. Your individual target may vary depending on your starting weight, health conditions, and whether you're using prescription weight loss medication alongside lifestyle changes.
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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.
How Weight Loss Rate Is Calculated
A safe weekly weight loss of 0.5 to 1 kg typically requires a calorie deficit of approximately 500 kcal per day. This means consuming 500 fewer calories than your body burns daily through activity and metabolism. For example, if your daily calorie burn is 2,500 kcal, aiming for 2,000 kcal intake could result in roughly 0.5 kg loss per week.
Weight loss isn't perfectly linear — some weeks you may lose more or less due to water retention, hormonal changes, or variations in food intake. The NHS emphasises that looking at trends over 2–4 weeks is more meaningful than daily fluctuations. Using our free progress tracker helps you spot patterns and stay motivated without obsessing over day-to-day changes.
- Sustainable loss: 0.5–1 kg per week
- Requires: approximately 500 kcal daily deficit
- Assessment period: review progress every 2–4 weeks
- Faster loss: only under medical supervision
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 Loss Medication and Weekly Loss
Prescription weight loss injections can support faster initial weight loss when combined with diet and exercise. For example, clinical trials of GLP-1 medications like Wegovy showed participants lost an average of 14–15% of body weight over approximately 12–16 weeks — though individual results vary significantly.
If you're considering weight loss medication through the NHS or private prescription, your prescriber will discuss realistic expectations for your situation. Weight loss medications work best alongside sustained lifestyle changes, not as a replacement. Our GLP-1 weight loss calculator can help you explore projected outcomes at different doses. Remember: any prescription weight loss treatment requires a clinical assessment to confirm suitability.
- 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 too fast?
Yes. The NHS recommends 0.5–1 kg per week for sustainable loss. Losing more than 1.5 kg weekly without medical oversight increases risks of muscle loss, nutritional deficiencies, and metabolic slowdown. If you're losing faster than expected, consult your GP — it may indicate an underlying issue or unsustainable behaviour.
Why does my weight fluctuate week to week?
Normal weekly variations of 0.5–1 kg are due to water retention, hormonal cycles, meal timing, exercise, and digestive contents. These aren't "real" fat loss changes. Track your weight at the same time each week and look for trends over 2–4 weeks rather than reacting to daily swings. Our progress tracker helps visualise genuine progress.
Can I lose weight faster with prescription medication?
Some people do achieve faster results with weight loss injections, but it varies individually. GLP-1 medications are prescription-only and require clinical assessment. They work alongside reduced-calorie diet and exercise, not instead of them. Your prescriber will discuss realistic timelines for your health profile.
What's a realistic weight loss target for 12 weeks?
At 0.5–1 kg per week, expect to lose 6–12 kg over 12 weeks. Using our free BMI calculator, you can see how this affects your BMI category and health metrics. Remember that initial loss includes water weight; fat loss becomes more significant after the first 2–3 weeks.
How do I know if my weight loss rate is healthy?
Your GP or a registered dietitian can assess whether your rate is safe for your circumstances. General NHS guidance is 0.5–1 kg weekly. If you have underlying health conditions, diabetes, or are taking medications, personalised medical advice is important. Use our BMI calculator and progress tracker to monitor your journey alongside professional support.
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.