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
Best Diet for Quick Weight Loss in the UK
Quick weight loss requires a combination of diet changes and medical support if appropriate. The NHS recommends losing weight at a sustainable rate of 0.5 to 1 kg per week, though prescription medication may help eligible adults achieve faster results. In the UK, weight management options range from self-help diets to specialist NHS services and prescription treatments. Understanding what works for your individual circumstances is key to achieving lasting results. Our free BMI calculator can help you assess your starting point and track progress toward your goals.
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 Management Options
For eligible adults, prescription weight management medications offer a clinically-supported approach to weight loss alongside diet and exercise. Three main prescription options are licensed in the UK:
- Mounjaro (tirzepatide) — a once-weekly injection. Clinical trials showed average weight loss of 15–21% of body weight over 72 weeks when combined with a reduced-calorie diet.
- Wegovy (semaglutide) — another once-weekly injection. Evidence from clinical trials demonstrated average weight loss of around 15% of body weight.
- Saxenda (liraglutide) — a daily injection option, average weight loss approximately 5–10% of body weight.
These medications work as GLP-1 (and in Mounjaro's case, GIP+GLP-1) receptor agonists, helping to regulate appetite and support feeling fuller after meals. All three are prescription-only and require a clinical assessment to determine eligibility. Individual results vary significantly based on lifestyle changes, adherence, and personal factors. Try our GLP-1 weight loss calculator to explore potential outcomes at different doses if you may be eligible.
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 Weight Loss Pathway and Private Access
In the UK, weight loss medication access depends on your BMI and health circumstances. NHS eligibility generally includes adults with a BMI of 30 or above, or 27–29.9 with weight-related conditions such as type 2 diabetes or high blood pressure. Access is through specialist tier 3 weight management services — your GP can refer you, though waiting times vary by region and may be lengthy.
Private access is available through GPhC-registered online prescribing services following a clinical assessment, without requiring an NHS referral. This route is faster but involves private costs. Before pursuing medication, discuss your circumstances with your GP — they can assess your individual eligibility, medical history, and whether prescription weight loss is appropriate for you alongside diet and lifestyle changes.
- 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.
What is the fastest safe weight loss diet?
The NHS recommends losing 0.5–1 kg per week as the safe, sustainable rate. Very gradual weight management (over 1.5 kg/week) risks muscle loss and nutritional deficiencies. For eligible adults, prescription weight management medications combined with a reduced-calorie diet may support faster results under medical guidance, but individual outcomes vary. Always consult your GP before starting any weight loss plan.
Are prescription weight loss injections available on the NHS?
Yes. Mounjaro, Wegovy, and Saxenda are licensed for weight management in the UK and available through NHS specialist weight management services. However, access is limited and referral pathways vary by region. Your GP can assess whether you may be eligible and refer you to a specialist tier 3 service. Waiting lists can be lengthy in many areas.
What diet works best alongside weight loss medication?
Prescription weight loss medications work most effectively with a reduced-calorie diet (typically 500 kcal below your daily needs) and increased physical activity. A balanced diet rich in protein, vegetables, and whole grains supports sustainable weight loss. Most clinical trials tested medication alongside dietary changes — medication alone is not effective without lifestyle modifications.
How can I check if I'm eligible for prescription weight loss treatment?
Eligibility generally requires a BMI of 30 or above, or 27–29.9 with weight-related health conditions. Use our free BMI calculator to check your BMI, then speak with your GP about your individual circumstances. Your GP can assess whether prescription weight loss medication is appropriate and refer you to specialist services if suitable.
What's the difference between Mounjaro and Wegovy?
Both are once-weekly injections, but Mounjaro (tirzepatide) uses a dual GIP+GLP-1 mechanism, while Wegovy (semaglutide) uses GLP-1 only. Clinical trials suggest Mounjaro may produce slightly higher average weight loss (15–21% vs 15%), though individual results vary greatly. Both require prescription and clinical assessment. Your prescriber will recommend the most suitable option for you.
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.