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 Will You Notice Weight Loss?
Weight loss timelines vary significantly between individuals, but most people begin noticing changes within 2–4 weeks when following a consistent reduced-calorie diet and lifestyle changes. With prescription weight loss medication like Wegovy (semaglutide), clinical trials showed participants experienced noticeable appetite reduction within the first few doses, though visible weight changes typically take 4–8 weeks to become apparent. Factors including current weight, metabolism, diet adherence, and physical activity all influence how quickly you'll see results. Track your progress using our free progress tracker to monitor both visible and measurable changes over time.
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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: How Quickly Can You Expect to See Weight Loss?
The NHS recommends a safe, sustainable weight loss rate of 0.5 to 1 kg (1 to 2 lbs) per week. At this pace, most people notice changes within 2–4 weeks, though initial loss is often water weight. With prescription weight loss medication such as Wegovy, timelines differ: clinical trials from the STEP-1 study showed noticeable appetite changes within 2–3 weeks, but meaningful weight loss (5% of body weight) typically appears by weeks 8–12. Individual responses vary significantly—some people notice changes sooner, others take longer depending on starting weight, metabolism, diet quality, and exercise consistency. Factors like water retention, hormonal cycles (in women), and muscle gain from exercise can temporarily mask fat loss on the scales.
- Weeks 1–2: Often water weight loss; clothes may feel slightly looser
- Weeks 2–4: Energy levels may improve; appetite reduction may become noticeable
- Weeks 4–8: Visible changes in face, neck, and waistband; weight loss becomes measurable
- Weeks 8–12: Significant progress becomes apparent; BMI category may shift
- Weeks 12+: Sustained loss continues with consistent lifestyle adherence
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.
Visible Signs of Weight Loss Beyond the Scales
Weight loss isn't always reflected immediately on the scales. Many people notice non-scale victories first: clothes fitting better, improved energy, better sleep quality, reduced joint pain, or easier breathing during exercise. These changes often occur before significant weight loss is visible. For objective tracking, you can measure waist circumference, take progress photos, or monitor how you feel during physical activity. Calculate your BMI using our free BMI calculator to track how your weight relates to your health, though remember that BMI is a screening tool and doesn't account for muscle mass. Some people taking prescription weight management medication notice appetite suppression and reduced food cravings within days, even before weight changes become visible—this itself is a sign the medication is working alongside your lifestyle changes.
- 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 long before you see weight loss results?
Most people notice visible changes within 4–8 weeks with consistent diet and exercise. With prescription GLP-1 weight loss medication, appetite reduction may occur within 2–3 weeks, but physical weight loss typically takes 4–12 weeks to become noticeable. Individual timelines vary based on starting weight, metabolism, and adherence.
Will I see weight loss in my face first?
Typically, weight loss becomes visible first in the face, neck, and upper body before the abdomen and lower body. This varies between individuals. Some people notice changes in how clothes fit before seeing scale changes—this is normal and a positive sign of progress.
What counts as successful weight loss?
The NHS considers 0.5–1 kg per week sustainable and healthy. Even a 5% reduction in body weight can improve blood pressure, blood sugar control, and cardiovascular health. Set realistic expectations—steady, gradual loss is more sustainable than rapid loss.
Can prescription weight loss medication speed up results?
Yes. Wegovy (semaglutide) and other GLP-1 medications may help achieve faster results than diet alone. Clinical trials showed average weight loss of 14–15% over 68 weeks. However, results vary individually and depend on combining medication with lifestyle changes.
Should I weigh myself daily to track weight loss?
Weigh yourself weekly or bi-weekly rather than daily—daily fluctuations from water retention, food volume, and hormonal changes can be discouraging. Use our free progress tracker to log weekly weights and spot patterns. Focus on how you feel and clothes fit, not just scale numbers.
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.