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
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Calculate Weight Loss With UK Prescription Medications
If you're looking to calculate weight loss and understand your options, prescription weight loss medications are now available in the UK for eligible adults. Mounjaro, Wegovy, and Saxenda are evidence-based treatments that work alongside diet and exercise. This guide explains how these medications work, who qualifies, and how to access them through the NHS or private prescribers. Use our free GLP-1 weight loss calculator to see potential projected results at different doses.
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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-Licensed Weight Loss Medications and Eligibility
Three main prescription options are available in the UK for weight management:
- Mounjaro (tirzepatide) — a once-weekly dual GIP and GLP-1 receptor agonist. Clinical trials showed average weight loss of around 15–21% of body weight alongside reduced-calorie diet and exercise.
- Wegovy (semaglutide) — a once-weekly GLP-1 injection with average weight loss of approximately 15% of body weight in clinical trials.
- Saxenda (liraglutide) — a daily GLP-1 injection, effective for weight management in eligible adults.
To be eligible for prescription weight loss UK treatment, you must have a BMI of 30 or above, or a BMI of 27–29.9 with weight-related health conditions such as type 2 diabetes, high blood pressure, or cardiovascular disease. Adults of South Asian, Chinese, Black African, or Black Caribbean heritage may qualify at lower BMI thresholds due to higher health risks at these levels. Calculate your BMI now using the free calculator on this page to check where you stand.
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 Access vs Private Prescribing — How to Get Started
NHS access: Prescription weight loss medications are available through specialist tier 3 weight management services, typically following referral from your GP. Availability and waiting times vary significantly by region. Contact your GP to ask about referral pathways in your area.
Private access: Many GPhC-registered prescribers offer online consultations for weight loss medication. Following clinical assessment, eligible patients receive a prescription that can be dispensed by regulated pharmacies.
Both routes require a clinical assessment to ensure the medication is appropriate for your individual health. Your GP is the best first point of contact if you want to explore prescription weight loss options, discuss your BMI, or understand whether you meet eligibility criteria for NHS 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 do I calculate my potential weight loss with these medications?
Use our free GLP-1 weight loss calculator on this page to estimate potential results. Clinical trials for Mounjaro showed average weight loss ranging from 15% at 5mg up to 21% at 15mg. Results vary between individuals and depend on diet, exercise, and consistency with the medication.
What's the difference between Mounjaro and Wegovy?
Mounjaro is a dual GIP and GLP-1 receptor agonist with average weight loss of 15–21%, while Wegovy is a GLP-1 agonist only with average loss around 15%. Both are once-weekly injections. Mounjaro has a wider dose range (2.5–15mg) compared to Wegovy (0.25–2.4mg).
Am I eligible for prescription weight loss medication on the NHS?
NHS eligibility typically requires a BMI of 30 or above, or 27–29.9 with weight-related health conditions like diabetes or high blood pressure. Lower thresholds apply for South Asian and Black African heritage adults. Ask your GP about referral to specialist weight management services in your area.
How quickly will I lose weight on these medications?
The NHS recommends losing 0.5–1kg per week for sustainable results. Prescription medications support this when combined with dietary changes and exercise. Most people see gradual weight loss over weeks and months, not rapid changes. Individual results vary significantly.
Can I get prescription weight loss medication privately if I don't qualify for NHS treatment?
Yes. Private prescribers can assess eligibility independently following an online consultation. However, they use similar clinical criteria to the NHS. Always ensure you're using a GPhC-registered prescriber and that any medication comes from a regulated pharmacy.
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.