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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Quick Weight Loss Diet — What Works in the UK
Losing weight quickly is appealing, but the safest approach is gradual and sustainable. The NHS recommends losing 0.5 to 1 kg per week through a combination of reduced-calorie diet and increased physical activity. This guide explains realistic weight loss timescales, evidence-based diet methods, and when prescription weight management options like GLP-1 injections might support your goals alongside lifestyle changes.
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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.
Safe Weight Loss Rates and Evidence-Based Approaches
The NHS weight loss guidance emphasises sustainable progress over rapid results. Losing 0.5 to 1 kg per week is considered safe and achievable for most adults and typically requires a calorie deficit of around 500 kcal per day. Very gradual weight management (more than 1.5 kg per week) increases the risk of muscle loss, nutrient deficiency, and is not recommended without medical supervision.
Evidence-based diet approaches for weight management UK include:
- Calorie deficit dieting — consistently consuming fewer calories than you burn, tracked using food apps or food diaries
- Intermittent fasting — 16:8 or 5:2 methods — clinical evidence supports modest weight loss comparable to standard calorie restriction
- Low carbohydrate diet — effective short-term; long-term outcomes similar to calorie restriction when adherence is comparable
- Mediterranean diet — strong evidence for cardiovascular health and sustainable weight management
- Increased physical activity — resistance training helps preserve muscle during weight loss
Try our free BMI calculator to establish your baseline, then use our weight loss projection calculator to estimate realistic timescales for your personal goals.
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.
When Quick Weight Loss Diet Alone May Not Be Enough
For some adults, diet and exercise alone are insufficient or take too long. In these cases, prescription weight loss medication may be considered. GLP-1 weight loss injections like Wegovy (semaglutide) and Mounjaro (tirzepatide) are licensed in the UK for weight management and are prescribed alongside diet and activity changes, not instead of them. Clinical trials showed adults on GLP-1 medication lost an average of 15–21% of their body weight — though individual results vary significantly.
Access through the NHS requires referral to a specialist tier 3 weight management service from your GP. Private prescription options are available without NHS referral. A licensed prescriber will assess whether prescription weight loss medication is appropriate for your individual circumstances based on your BMI and health profile.
- 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 weight can I realistically lose in a month with diet alone?
The NHS recommends losing 0.5 to 1 kg per week through diet and activity combined, which equates to roughly 2–4 kg per month. This is safe and sustainable. Faster loss is possible but increases risks of muscle loss and nutrient deficiency. Use our weight converter to see how monthly targets translate between kg and stone.
Is gradual weight management dangerous?
Yes, very gradual weight management (more than 1.5 kg per week) without medical supervision increases risks of muscle loss, gallstones, nutrient deficiency, and metabolic slowdown. Sustainable loss of 0.5–1 kg per week is safer and more likely to be maintained long-term.
Can prescription weight loss injections help with a quick weight loss diet?
GLP-1 medications like Wegovy and Mounjaro may support weight loss when combined with diet and exercise changes. In clinical trials, these medications helped adults lose an average of 15–21% of body weight — but individual results vary. They are prescription-only and require clinical assessment.
What should I do first — diet or medication?
The NHS pathway recommends starting with diet, exercise, and behaviour change support (Tier 1 and 2). If progress is insufficient after 3–6 months, your GP can refer you to specialist weight management services (Tier 3) where medication may be considered as an option.
How do I know if my weight loss diet is safe?
A safe approach involves: gradual loss (0.5–1 kg per week), balanced nutrition, increased activity, and ideally support from a healthcare professional. Check your BMI using our free calculator to understand your baseline, and consult your GP if you're considering gradual weight management or medication options.
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.