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 The Fastest Weight Loss Method in the UK?
The fastest weight loss method available in the UK is prescription weight management medication, combined with a reduced-calorie diet and increased physical activity. Medications like Mounjaro and Wegovy are licensed for adults with obesity or overweight with health conditions, and clinical trials show they can help achieve significant results. However, "fastest" doesn't mean unsustainable — the NHS recommends safe weight loss of 0.5–1 kg per week. Your eligibility depends on your BMI and individual health circumstances, and you'll need a prescription from a GP or licensed prescriber following a clinical assessment.
10,000+ calculations today · NHS-aligned thresholds · 100% free
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-Licensed Prescription Weight Loss Medications
Three prescription-only medications are licensed in the UK specifically for weight management: Mounjaro (tirzepatide), Wegovy (semaglutide), and Saxenda (liraglutide). Mounjaro and Wegovy are injected once weekly and are typically the fastest-acting options, with clinical trials showing average weight loss of 15–21% of body weight over several months. Saxenda is a daily injection with slightly lower average weight loss. All three work by mimicking hormones that regulate appetite and help you feel fuller after eating.
Eligibility for prescription weight loss medication in the UK requires a BMI of 30 or above, or 27 or above with weight-related health conditions such as type 2 diabetes, high blood pressure, or sleep apnoea. If you're of South Asian, Chinese, Black African, or Black Caribbean heritage, lower BMI thresholds may apply. Our free GLP-1 weight loss calculator can help you estimate potential weight loss at different doses if you're considering prescription medication.
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.
NHS vs Private Access — Getting Started
NHS route: Referral through your GP to a specialist tier 3 weight management service is free, though waiting lists can be lengthy in many regions. Not all areas have equal access, and availability depends on your local Integrated Care Board (ICB).
Private route: You can access prescription weight loss medication through a GPhC-registered online pharmacy following a private clinical assessment with a UK-licensed prescriber — no NHS referral needed. This is typically faster but involves a cost of £129–£320+ per month depending on dose.
Either way, start by speaking with your GP about your weight management goals. They can assess whether medication is appropriate for you, discuss NHS options, and provide personalised guidance. Use our free BMI calculator above to understand your current BMI category and help frame the conversation with your healthcare provider.
- 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.
What is the single fastest weight loss method that works?
Prescription medications like Mounjaro and Wegovy, combined with diet and exercise, show the fastest results in clinical trials — average weight loss of 15–21% over several months. However, individual results vary significantly, and medication works best alongside lifestyle changes, not as a replacement for them.
Can I lose weight faster than 1 kg per week safely?
The NHS recommends 0.5–1 kg per week as the sustainable, safe rate. Faster weight loss is possible with medical supervision (such as very low-calorie diets in specialist services), but it increases the risk of muscle loss, nutrient deficiency, and regaining weight. Speak to your GP about safe options for your situation.
Do I need to be referred to the NHS to get weight loss medication?
Not necessarily. NHS access requires a GP referral to specialist services, which can involve waiting lists. Private access through a GPhC-registered online pharmacy is available without NHS referral — you'll need a clinical assessment with a UK-licensed prescriber, but the process is typically faster.
What is the difference between Mounjaro and Wegovy for fast weight loss?
Both are once-weekly injections, but Mounjaro (tirzepatide) acts on two hormone pathways and showed slightly higher average weight loss (up to 21%) in clinical trials, whilst Wegovy (semaglutide) showed around 15% average loss. Both work well; prescriber preference and individual factors determine which is more suitable for you.
How can I find out if I'm eligible for prescription weight loss medication?
Check your BMI using our free BMI calculator on this page. If your BMI is 30 or above, or 27 or above with weight-related health conditions, you may be eligible. Arrange a conversation with your GP or access a private online clinical assessment to confirm eligibility and discuss the right option for you.
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.