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
When Can You See Weight Loss?
Weight loss takes time, and when you'll notice visible changes depends on your starting point, metabolism, and method. Most people see measurable weight loss within 2–4 weeks of consistent calorie deficit, though visible physical changes may take 6–8 weeks. If you're using prescription weight loss medication like Mounjaro or Wegovy, you may see results within 4 weeks at higher doses, with more significant changes visible by 12 weeks. Track your progress using our free progress tracker to monitor both the numbers and how you feel throughout your weight loss journey.
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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 Quickly Will You Notice Weight Loss?
The timeline for seeing weight loss depends on several factors: your starting weight, metabolism, diet adherence, and physical activity level. On average, weight loss becomes measurable within 7–10 days if you're in a calorie deficit, though this initial loss includes water weight. Visible physical changes — like looser clothing or facial definition — typically appear after 3–6 weeks of consistent effort.
For NHS weight loss programmes, the recommended rate is 0.5–1 kg per week, which means you'd expect to see approximately 2–4 kg lost in the first month. With GLP-1 weight loss injections like Mounjaro or Wegovy, clinical trials showed average weight loss of 15–21% over 72 weeks, with many users reporting noticeable appetite reduction and initial weight changes within the first 4 weeks. However, individual results vary significantly — some people see faster progress, others more gradual changes.
Use our free BMI calculator to establish your baseline, then track your weight regularly every 1–2 weeks rather than daily, as daily fluctuations can be misleading.
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.
Realistic Expectations at Different Time Points
Week 1–2: Initial weight loss (often water weight). Clothes may feel slightly looser. Energy levels may fluctuate as your body adapts.
Week 3–4: Measurable fat loss begins. You may notice mood improvements and increased energy. Friends may not comment yet, but you'll feel the difference.
Week 6–8: Visible physical changes become apparent. Clothes fit noticeably differently. Friends and family may comment. Progress tracker data shows clear trends.
Week 12+: Significant visible transformation. Sustained weight loss becomes your new normal. Health markers (blood pressure, blood sugar) often improve at this stage.
For prescription weight loss medication: Appetite changes may be noticeable within days; weight loss acceleration typically occurs by week 2–4. Always discuss progress expectations with your GP or prescriber during your weight management in the UK.
- 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 will I lose in the first week?
Initial weight loss is typically 1–2 kg in the first week, though much of this is water weight and glycogen depletion rather than fat loss. The rate slows after week one. Sustainable fat loss averages 0.5–1 kg per week according to NHS guidance. Individual variation is significant based on starting weight, metabolism, and diet adherence.
Will I see visible changes before the scales move?
Usually, the opposite occurs — the scales move first (water weight), then visible changes follow. However, some people notice looser clothing or improved posture within 2–3 weeks before significant scale movement. Progress tracker data and measurements (waist, chest, arms) often reveal changes the scales don't yet reflect.
When should I expect Mounjaro or Wegovy to show results?
STEP clinical trials showed semaglutide (Wegovy) users experienced appetite reduction within the first few injections. Average measurable weight loss typically appears by week 2–4, with more significant results by 12 weeks. Results depend on dose, adherence, and lifestyle changes alongside medication. Individual timescales vary.
Is it normal to see no weight loss in the first two weeks?
Yes, especially if you started with low water weight or have a slower metabolism. Weight loss is not always linear — plateaus happen. Ensure you're in a genuine calorie deficit by tracking food intake carefully. Use our BMI calculator and progress tracker to monitor other markers beyond just weight (how you feel, energy, clothes fit).
Should I weigh myself daily or weekly?
Weekly or bi-weekly is recommended by NHS weight management services. Daily weighing can cause discouragement due to water retention, hormonal fluctuations, and food digestion timing. Pick the same day and time each week (e.g., Friday morning) for consistency. Our progress tracker helps you log weekly data and spot trends without obsessing over daily fluctuations.
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.