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
Weight Loss Calculator & Your Goal Weight — UK Medication Options
Setting a realistic weight loss goal is the first step towards sustainable health improvement. If you're considering prescription weight management as part of your weight loss strategy, it's important to understand what options are available in the UK, how they work, and whether you might be eligible. This guide explains prescription weight loss medications, how to calculate your goal weight, and how to access treatment through both NHS and private healthcare routes.
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 medicines are currently licensed in the UK specifically for weight management: Mounjaro (tirzepatide), Wegovy (semaglutide), and Saxenda (liraglutide). All are GLP-1 receptor agonists (Mounjaro is a dual GIP and GLP-1 agonist), which work by helping to reduce appetite and support feeling fuller after eating.
In clinical trials, these medications helped participants achieve average weight loss of 14–21% of their body weight when used alongside reduced-calorie diet and increased physical activity. However, individual results vary significantly — some people lose more, some less. You can use our free GLP-1 weight loss calculator to estimate potential outcomes at different doses.
Eligibility in the UK: You may be eligible if you 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. For adults of South Asian, Chinese, Black African, or Black Caribbean heritage, the NHS recommends lower BMI thresholds. A prescriber will assess your individual circumstances before any prescription is issued.
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 — How to Get Started
NHS route: Prescription weight loss medications are available through NHS specialist weight management services (Tier 3/4). Your GP can refer you to your local service, though waiting times vary significantly by region — some areas have waiting lists of many months. NHS weight loss injections are typically prescribed alongside behaviour change support.
Private route: You can access prescription weight loss treatment through GPhC-registered online prescribers without an NHS referral. A private consultation and clinical assessment are required before a prescription is issued. Costs vary by medication and dose, typically ranging from £129–£320 per month.
Whichever route you choose, speak with your GP first. They can advise whether prescription weight loss treatment is appropriate for you, discuss your weight loss goals, and help you understand the NHS options available in your area. Use our free BMI calculator to check your current BMI — this information will be helpful when discussing options with your doctor.
- 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 realistic weight loss goal?
A sustainable goal is typically 5–10% of your current body weight over 3–6 months. For example, if you weigh 100kg, losing 5–10kg is realistic. Use the weight converter on this page to check this in stone and pounds. Our progress tracker can help you log your journey. Always discuss specific goals with your GP or a healthcare professional.
Are weight loss injections available on the NHS?
Yes. Mounjaro, Wegovy, and Saxenda are all available through NHS specialist weight management services. Your GP can refer you, but availability varies significantly by region. Some areas have waiting lists. You can also access these medications privately through a UK-licensed prescriber without an NHS referral.
What does "BMI of 27–29.9 with weight-related conditions" mean?
It means you may be eligible for prescription weight loss treatment if your BMI falls between 27 and 29.9 AND you have a condition like type 2 diabetes, high blood pressure, cardiovascular disease, or sleep apnoea. Use our free BMI calculator to check your current BMI, then discuss eligibility with your GP.
How much weight can I expect to lose with prescription medication?
Clinical trials showed average weight loss of 14–21% of body weight over 68–72 weeks when medication is combined with diet and physical activity. However, individual results vary significantly. Our GLP-1 weight loss calculator provides a personalised projection based on your current weight and dose.
Do I need to change my diet and exercise if I take weight loss medication?
Yes. Prescription weight loss medications work best alongside a reduced-calorie diet and increased physical activity. These medications support weight loss but are not a substitute for lifestyle changes. Your GP or a specialist weight management service can provide dietary and exercise guidance tailored to your needs.
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.