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
Does Drinking Water Help With Weight Loss?
Yes, staying hydrated supports weight loss efforts. Drinking water can help reduce appetite, boost metabolism slightly, and support your body during weight loss. However, water alone isn't enough for significant weight loss. In the UK, adults struggling with their weight now have access to prescription weight loss medications alongside lifestyle changes like better hydration and physical activity. Our free BMI calculator can help you understand your current weight status, and if you're eligible, your GP can discuss prescription options available in the UK.
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 Prescription Weight Loss Options for Eligible Adults
If drinking water and lifestyle changes aren't delivering results, prescription weight loss medication may be an option. Three medications are currently licensed in the UK for weight management:
- Mounjaro (tirzepatide) — a once-weekly GLP-1 and GIP receptor agonist injection that may help reduce appetite and support feeling fuller after meals. Clinical trials showed average weight loss of 15–21% of body weight alongside diet and exercise.
- Wegovy (semaglutide) — a once-weekly GLP-1 receptor agonist injection. Clinical evidence suggests average weight loss of around 15% of body weight when used with reduced-calorie diet and increased physical activity.
- Saxenda (liraglutide) — a once-daily GLP-1 injection, available through specialist NHS services and private prescribing.
All three are prescription-only medicines requiring a clinical assessment to determine suitability. Our GLP-1 weight loss calculator can help you explore projected outcomes at different doses — though individual results vary significantly.
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 — What Are You Eligible For?
UK adults with a BMI of 30 or above, or 27–29.9 with weight-related health conditions, may be eligible for prescription weight loss treatment. NHS access is through tier 3 specialist weight management services — referred by your GP, though waiting lists vary by region. Private access is through online prescribing services following a clinical assessment, without NHS referral.
Before exploring medication, use our free weight converter to understand your weight in both metric and imperial measurements, then speak to your GP. They can assess your individual health, discuss whether prescription medication is appropriate for you, and explain next steps in your weight management journey. Hydration and lifestyle changes remain important alongside any medical 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.
Does drinking water alone cause weight loss?
Drinking water supports weight loss by reducing appetite and boosting metabolism slightly, but it's not a standalone solution. Sustainable weight loss requires a calorie deficit, physical activity, and often behavioural changes. For significant results, many UK adults combine hydration with dietary changes and, if eligible, prescription medication prescribed by a healthcare professional.
What is the difference between Mounjaro and Wegovy?
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, while Wegovy (semaglutide) is a GLP-1-only medication. Both are once-weekly injections. Clinical trials suggest Mounjaro may help achieve slightly higher average weight loss, but both medications work best alongside reduced-calorie diet and exercise. Individual results vary significantly.
How do I know if I'm eligible for prescription weight loss medication in the UK?
You may be eligible if your BMI is 30 or above, or 27–29.9 with weight-related conditions like type 2 diabetes, high blood pressure, or cardiovascular disease. Lower thresholds apply if you're of South Asian, Chinese, Black African, or Black Caribbean heritage. Your GP can assess your eligibility and refer you to specialist services if appropriate.
Can I get weight loss injections through the NHS in the UK?
Yes. Mounjaro and Wegovy are available through NHS specialist tier 3 weight management services for eligible adults. Access is through GP referral. However, NHS availability and waiting times vary significantly by region. Private prescribing services also offer these medications following an online clinical assessment, without NHS referral.
Should I drink more water if I'm taking Mounjaro or Wegovy?
Yes, staying well hydrated is important when taking any weight loss medication. These injections can cause nausea and digestive changes, and adequate water intake helps manage these side effects and supports overall health. However, always follow your prescriber's specific guidance on fluid intake and any dietary recommendations during treatment.
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.