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 Quickly Can I Lose Weight on Mounjaro?
Weight loss on Mounjaro typically becomes noticeable within the first 4–8 weeks, though individual results vary significantly. In clinical trials, adults taking Mounjaro lost an average of 15–21% of their body weight over 72 weeks alongside a reduced-calorie diet and increased physical activity. The speed of weight loss depends on your starting weight, dose, and how closely you follow lifestyle changes. Whether you access Mounjaro through the NHS or privately affects how quickly you can start treatment.
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 Cost and Access Routes for Mounjaro
Mounjaro (tirzepatide) is available in the UK through two main routes: NHS specialist weight management services and private prescription via online consultations. NHS access requires referral to a tier 3 specialist weight management service from your GP, but availability varies significantly by region and waiting lists can extend several months. Private prescription routes are faster — typically available within days following an online clinical assessment with a UK-licensed prescriber. Private costs range from approximately £129–£320 per month depending on your dose, with prices based on the weekly injection dosage: starting doses (2.5–5 mg) are less expensive than higher maintenance doses (10–15 mg). A KwikPen containing four weekly injections costs vary by provider. When budgeting, remember you'll also need a reduced-calorie diet and increased physical activity for optimal results alongside your weekly weight loss injection UK prescription.
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: Timeline and Getting Started
The NHS route offers free treatment but involves waiting times — often months to years in some regions due to high demand and limited specialist services. Your GP can refer you, but availability depends on your local Integrated Care Board (ICB). The private route is faster: you complete an online consultation, a registered prescriber assesses your suitability, and your prescription is dispensed by a GPhC-registered pharmacy, often within 48 hours. Both routes require you to have a BMI of 30 or above, or 27–29.9 with weight-related conditions (type 2 diabetes, hypertension, sleep apnoea). Use our GLP-1 weight loss calculator above to estimate potential weight loss at your target dose, and try our free BMI calculator to confirm your eligibility for treatment.
- 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 per week on Mounjaro?
Weight loss varies, but clinical data shows an average loss of 0.5–1 kg per week once you've titrated to maintenance dose (typically weeks 16+). Faster initial loss is common due to water loss and dose escalation. Individual results depend on your starting weight, adherence to diet and exercise, and how your body responds to the medication.
Is Mounjaro faster than Wegovy for weight loss?
Mounjaro (tirzepatide) showed slightly higher average weight loss (~21% body weight) than Wegovy semaglutide (~15% body weight) in separate clinical trials, but these are not direct head-to-head comparisons. Individual results vary considerably, and both are effective. Your prescriber will recommend the most suitable option based on your health profile.
How long does it take to reach the maximum Mounjaro dose?
Dose titration takes 20 weeks. You start on 2.5 mg, increasing by 2.5 mg every 4 weeks until you reach 15 mg (the maximum dose). Most people see meaningful weight loss during escalation, with continued loss at maintenance dose.
Can I get Mounjaro through my NHS GP?
Your GP cannot prescribe Mounjaro directly for weight loss — it requires referral to a specialist tier 3 weight management service. Waiting times vary by region (typically 6–18 months in many areas). Private prescription is a faster alternative if you meet eligibility criteria.
What happens after I stop taking Mounjaro?
Weight loss is typically maintained through the lifestyle changes (diet and exercise) you've built during treatment. However, some weight regain may occur if healthy habits aren't sustained long-term. Mounjaro works best as part of a comprehensive weight management approach, not as a standalone solution.
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.