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 To See Weight Loss Results
Weight loss results typically take 2 to 4 weeks to become noticeable with consistent dietary changes and increased physical activity. If you're considering prescription weight management in the UK, the timeline depends on which medication you use, your starting weight, and how your body responds. Understanding realistic timelines helps you stay motivated and set achievable goals. This guide covers what to expect with different approaches to weight loss in the UK.
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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.
UK Prescription Weight Loss Options and Timelines
Three prescription medications are licensed for weight management in the UK:
- Mounjaro (tirzepatide) — Results often visible within 4–8 weeks; average weight loss of 15–21% body weight over several months in clinical trials
- Wegovy (semaglutide) — Noticeable changes typically within 2–4 weeks; average weight loss around 15% body weight at the maximum dose
- Saxenda (liraglutide) — Daily injection; results may appear within 4–6 weeks with consistent use
All three require a prescription and clinical assessment. Weight loss medication works best alongside a reduced-calorie diet and increased physical activity. Individual responses vary significantly — some people see results within weeks, while others take 8–12 weeks. Our GLP-1 weight loss calculator can help estimate potential timelines based on different doses and your starting weight. Your prescriber will monitor your progress and adjust your dose if needed to optimise results.
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.
Getting Started: NHS vs Private Access
In the UK, you can access prescription weight loss medication through NHS specialist weight management services (tier 3) or private online prescribing. NHS access typically requires a GP referral and assessment through your local integrated care board (ICB) — waiting lists vary by region, sometimes lasting many months. Private access is faster: a UK-licensed prescriber assesses your eligibility online, and medication is dispensed by a registered pharmacy if appropriate. Before starting any weight loss medication, discuss your health history, current medications, and realistic goals with your GP or prescriber. Using our free BMI calculator above helps you track where you stand on the NHS health scale and sets a baseline for measuring progress throughout your weight loss journey.
- 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 quickly will I see weight loss results with GLP-1 medication?
Most people notice changes within 2–4 weeks of starting, though results vary. By 8–12 weeks, weight loss becomes more significant. Clinical trials show average losses of 15–21% body weight over several months. Remember that individual responses differ based on dose, adherence, diet, and activity level. Your prescriber will adjust your dose over several weeks to find the right level for you.
What if I don't see results within the first month?
One month is still early in treatment. Prescription weight loss medications often require 4–8 weeks to show noticeable results as your body adjusts and your dose is gradually increased. Ensure you're following the recommended reduced-calorie diet and physical activity guidance. If you have concerns after 8–12 weeks, discuss this with your prescriber — they may adjust your dose or review your overall approach.
Can I speed up weight loss results?
The safest, most sustainable approach is losing 0.5–1 kg per week through consistent dietary changes and increased activity alongside medication. Trying to lose weight faster can result in muscle loss, nutritional deficiencies, and is not recommended without medical supervision. Your prescriber monitors your progress and ensures you're losing weight safely.
Do I need to diet and exercise while taking weight loss medication?
Yes, prescription weight loss medications work best alongside a reduced-calorie diet and regular physical activity. Medication helps reduce appetite and cravings, but lifestyle changes are essential for sustainable results. Studies show that medication alone without dietary changes produces significantly better results than diet or exercise alone.
How do I know if weight loss medication is right for me?
You may be eligible if your BMI is 30 or above, or 27 or above with a weight-related health condition (such as type 2 diabetes, high blood pressure, or sleep apnoea). A GP or licensed prescriber will assess your individual health history, medications, and suitability. This assessment is crucial — not everyone should take these medications.
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.