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
Quick Weight Loss and Water — What the Evidence Shows
Water alone cannot create quick weight loss, though staying hydrated supports any weight management effort. The NHS recommends losing weight at a rate of 0.5 to 1 kg per week for sustainable results — faster loss requires medical supervision. This guide explains how water fits into weight loss, what "quick" actually means for health, and the evidence-based options available for those seeking weight management 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.
Water, Hydration, and Weight Loss — The Reality
Drinking water may help with weight management, but not in the way myths suggest. Water itself contains no calories and doesn't directly burn fat. However, staying properly hydrated supports your body's metabolism and can help you feel fuller before meals, potentially reducing overall calorie intake.
The evidence shows:
- Drinking 500ml of water before meals may slightly reduce food intake in some people
- Proper hydration supports kidney function and helps your body process weight loss efficiently
- Thirst is often mistaken for hunger — staying hydrated can reduce unnecessary snacking
- Water has no calories, making it an ideal alternative to sugary drinks and alcohol
However, water is not a weight loss solution on its own. True weight management requires a calorie deficit alongside physical activity. Using our free BMI calculator above can help you understand your current health status and set realistic targets.
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.
Quick Weight Loss — Why It Matters (And Why It's Risky)
Losing weight very quickly — more than 1.5 kg per week — carries health risks including muscle loss, nutritional deficiency, gallstones, and metabolic slowdown. The NHS specifically recommends gradual weight loss as the safest approach for most adults.
For those seeking faster results, prescription weight loss medication is available in the UK through NHS specialist services or private prescribing. These GLP-1 medications like Mounjaro and Wegovy work alongside diet and exercise to support more significant weight loss when clinically appropriate. Our GLP-1 weight loss calculator can help you understand potential outcomes if you're considering medication. Always discuss weight loss medication with your GP or a licensed prescriber to assess suitability based on your individual health.
- 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 water should I drink daily for weight loss?
The NHS recommends 6–8 glasses of water daily for general health. More water doesn't accelerate weight loss — excess water is simply excreted. Focus on consistent, adequate hydration rather than excessive intake. Replace sugary drinks with water to reduce calorie consumption naturally.
Will drinking water alone help me lose weight quickly?
No. Water alone cannot create the calorie deficit needed for weight loss. Quick weight loss requires a combination of reduced calorie intake, physical activity, and sometimes medical support. The NHS advises losing 0.5–1 kg per week as a sustainable, safe rate.
Can water reduce bloating and water weight quickly?
Temporary water weight fluctuations (1–2 kg) are normal and related to hormones, sodium intake, and hydration levels — not fat loss. These changes reverse quickly. Sustainable weight loss means losing body fat, which requires consistent dietary and lifestyle changes over weeks and months.
What's the safest way to lose weight quickly in the UK?
Consult your GP or a registered weight management service. The NHS provides tier 1–4 weight management support. For those meeting specific criteria (BMI ≥30, or ≥27 with health conditions), prescription weight loss medication through NHS specialist services or private prescribing may be appropriate alongside lifestyle changes.
How does prescription weight loss medication work compared to water and diet alone?
GLP-1 medications like Wegovy and Mounjaro work by regulating appetite hormones, helping you feel fuller on smaller portions. Clinical trials showed average weight loss of 14–21% of body weight. These work alongside calorie deficit and exercise, not instead of them. Always consult a prescriber to assess eligibility.
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.