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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Weight Loss Calculation: UK Prescription Medication Options
Calculating your weight loss potential helps you set realistic goals and understand what prescription medication might achieve. In the UK, several licensed medications can support weight management when combined with dietary changes and increased physical activity. Understanding how these medications work, who is eligible, and what clinical evidence shows can help you decide whether to speak with your GP about weight loss options available through the NHS or private prescribing services.
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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 Prescription Weight Loss Medications
Three prescription medications are licensed in the UK for weight management in eligible adults:
- Mounjaro (tirzepatide) — a dual GIP and GLP-1 receptor agonist with once-weekly injections. Clinical trials showed average weight loss of approximately 15–21% body weight over 72 weeks at maximum dose, alongside a reduced-calorie diet and increased physical activity.
- Wegovy (semaglutide) — a GLP-1 receptor agonist, also once-weekly. Clinical data from STEP trials demonstrated average weight loss of approximately 15% body weight at the maximum 2.4 mg dose.
- Saxenda (liraglutide) — a daily GLP-1 injection, the longest-established option. Average weight loss ranges from approximately 5–10% body weight depending on individual response.
All three are prescription-only and require clinical assessment. Individual results vary significantly — these figures are clinical trial averages, not assured outcomes for any individual.
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: Finding Your Eligible for Weight Loss Support
In the UK, weight loss medication is available through two routes. NHS access involves referral to a tier 3 specialist weight management service — typically through your GP. Availability varies by region and waiting times can be lengthy. Private access is through GPhC-registered online pharmacies following a consultation with a UK-licensed prescriber, and does not require NHS referral.
You may be eligible if you have a BMI of 30 or above, or BMI 27–29.9 with a weight-related health condition (such as type 2 diabetes, high blood pressure, or sleep apnoea). Lower BMI thresholds may apply if you are of South Asian, Chinese, Black African, or Black Caribbean heritage. Use our free BMI calculator to check your BMI, and speak with your GP about what options are available for you personally.
Use our free GLP-1 weight loss calculator to estimate potential weight loss at different medication doses — this can help inform your conversation with a healthcare professional. Remember that weight loss calculations are projections based on clinical trial data; your actual results will depend on adherence to the medication, dietary changes, physical activity levels, and individual factors including metabolism and genetics.
Start by calculating your current BMI using our free BMI calculator and weight converter, then discuss prescription options with your GP or a licensed prescriber to understand what's realistic for your individual circumstances.
- 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 is weight loss with GLP-1 medication calculated?
Weight loss is typically expressed as a percentage of your starting body weight. Clinical trials report average outcomes — for example, "clinically studied weight loss" means a person weighing 100kg might lose approximately 15kg on average. Our GLP-1 weight loss calculator uses this data to provide estimates, but individual results vary based on medication adherence, diet, activity, and metabolism.
What's the difference between weight loss calculation in NHS vs private services?
The calculation method is the same — both are based on clinical trial data. The difference is in access. NHS specialist services provide assessment and prescription through the health service; private services offer prescription following an online consultation. Both require clinical assessment to confirm eligibility and suitability.
How do I calculate my eligibility for weight loss medication in the UK?
Use our free BMI calculator to determine your BMI. If your BMI is 30 or above, or 27–29.9 with a weight-related health condition (type 2 diabetes, high blood pressure, sleep apnoea), you may be eligible. South Asian, Chinese, Black African, or Black Caribbean adults may qualify at lower BMI thresholds. Your GP can confirm eligibility based on your individual health.
Can I calculate weight loss if I have type 2 diabetes?
Yes. If you have type 2 diabetes and are overweight or obese, weight loss medication may be suitable — your GP or prescriber will assess this. Diabetes is considered a weight-related health condition that may make you eligible even at a lower BMI. Our weight loss calculator can help estimate potential outcomes alongside your clinical consultation.
What factors affect weight loss calculations beyond medication?
Clinical calculations assume you're also following a reduced-calorie diet and increasing physical activity. Your actual weight loss depends on medication adherence, how strictly you follow dietary guidance, exercise frequency, sleep quality, stress levels, metabolism, genetics, and any underlying medical conditions. Use our progress tracker to log real results alongside calculations.
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.