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 Long Does It Take To See Weight Loss Results?
Seeing weight loss results takes time, and the timeline depends on your method, starting weight, and individual metabolism. Most people notice measurable changes within 4–8 weeks of consistent effort, though some see results earlier. Whether you're making lifestyle changes, following an NHS weight management programme, or exploring prescription weight loss medication like GLP-1 injections, understanding realistic timelines helps you stay motivated and track genuine progress. Our free BMI calculator and progress tracker can help you monitor changes as they happen.
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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.
Timeline for Different Weight Loss Approaches
Lifestyle changes (diet and exercise): Most people see noticeable results within 4–8 weeks of consistent calorie deficit and increased physical activity. The NHS recommends aiming for a weight loss of 0.5–1 kg per week, which means losing 2–4 kg (4–9 lbs) per month. Changes may be visible in how clothes fit or increased energy before the scales move.
- Week 1–2: Water weight loss (1–2 kg) but not fat loss yet
- Week 4–6: Clothes fit better, increased energy, 2–4 kg lost
- Week 8+: Measurable weight loss, improved fitness, visible body changes
- 3–6 months: Significant health improvements (blood pressure, blood sugar)
GLP-1 weight loss medication (Wegovy, Mounjaro): Clinical trials showed measurable weight loss within 4 weeks, with progressive results over 12–16 weeks as doses increase. Average weight loss of 15–21% of body weight occurred over 68–72 weeks in STEP and SURMOUNT trials, alongside reduced-calorie diet and increased physical activity. Individual results vary significantly.
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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.
What Affects How Fast You'll See Results
Several factors influence how quickly you notice weight loss results. Your starting weight matters — people with more weight to lose often see faster initial results. Age affects metabolism; younger people may lose weight faster than older adults. Genetics play a role in how your body distributes and loses fat. Consistency is critical — weight loss only happens with sustained calorie deficit, not sporadic effort. Medical conditions like thyroid problems, PCOS, or type 2 diabetes can slow results and should be discussed with your GP. Using our free progress tracker helps identify your personal rate and spot improvements beyond just the scales — such as energy levels, fitness, or how you feel in clothes.
- 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.
How much weight can I lose in the first week?
Initial weight loss in week 1 is often 1–2 kg, but this is mostly water weight as your body uses stored glycogen. True fat loss becomes visible after 2–3 weeks. The NHS recommends aiming for 0.5–1 kg per week for sustainable fat loss rather than rapid water weight fluctuation.
How long before I notice clothes fitting differently?
Most people notice clothes fitting better within 4–6 weeks of consistent weight loss. Tight areas like waist and shoulders usually show changes first. This can happen before significant scale weight loss because fat loss and muscle changes affect how your body looks and feels.
When do health benefits like blood pressure improvement appear?
NHS research shows that even a 5–clinically studied weight loss can improve blood pressure, blood sugar control, and cholesterol levels within 8–12 weeks. Larger health improvements (reduced diabetes medication, improved sleep apnoea) often take 3–6 months of sustained weight loss.
Do weight loss injections like Wegovy work faster than diet alone?
Clinical trials showed measurable weight loss with GLP-1 medication within 4 weeks, with progressive results over months as doses increase. Results appear faster than diet alone for some people, but Wegovy still requires a reduced-calorie diet and physical activity — medication supports these changes, it doesn't replace them.
What should I do if I'm not seeing results after 4 weeks?
If you've been consistent for 4 weeks with no change, review your calorie intake with your GP or a registered dietitian — you may need to adjust your approach. Medical conditions, medications, or metabolic factors could also affect results. Your GP can check for underlying causes like thyroid problems.
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.