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
Fasting Plan for Weight Loss — What Works in the UK
Fasting is an eating pattern that cycles between periods of eating and fasting, and it can be part of a weight management strategy in the UK. Intermittent fasting (like 16:8 or 5:2) may help create a calorie deficit, which is essential for weight loss. However, fasting alone isn't assured to work — it works best combined with a balanced diet, physical activity, and professional guidance. The NHS emphasises that sustainable weight loss happens at a rate of 0.5 to 1 kg per week. Before starting any fasting plan, especially if you have health conditions or take medications, always consult your GP.
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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.
How Fasting Plans Support Weight Loss
Fasting works by extending the time between your last meal and your next eating window, which can help reduce overall calorie intake without strict calorie counting. The most popular fasting approaches are:
- 16:8 (Time-Restricted Eating) — Fast for 16 hours, eat within an 8-hour window (e.g., noon to 8 PM). Evidence suggests this can create a moderate calorie deficit and support weight management in the UK.
- 5:2 (Modified Fasting) — Eat normally five days per week, restrict calories to 500–600 kcal on two non-consecutive days. Studies show modest weight loss, typically 4–8 kg over 8 weeks.
- Eat-Stop-Eat — Complete 24-hour fasts once or twice per week. Less common but may appeal to some people.
Fasting may help by slowing gastric emptying and potentially reducing hunger hormones, though individual results vary significantly. Combined with a reduced-calorie diet and increased physical activity, fasting can support weight loss goals. Use our free BMI calculator to track where your current weight sits on NHS guidelines, and monitor your progress with our weight loss progress tracker.
Clinically BackedWeight Loss
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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.
Fasting and Prescription Weight Loss Options
If fasting alone isn't delivering results, prescription weight loss medications like GLP-1 injections (including Mounjaro and Wegovy) may be considered. These are prescription-only and require clinical assessment by a GP or licensed prescriber. GLP-1 medications work by reducing appetite and supporting feeling fuller, which complements dietary approaches. In clinical trials, Wegovy users lost an average of 14.9% body weight over 68 weeks alongside diet and exercise — individual results vary. Whether you're exploring fasting, medication, or a combination approach, your GP can assess what's suitable for your health. Try our GLP-1 weight loss calculator to estimate potential outcomes, and use our weight converter to track your progress in kg, stone, or pounds — whichever you prefer.
- 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 fasting alone clinically studied weight loss?
No. Fasting can help create a calorie deficit, but weight loss depends on overall calorie intake, physical activity, genetics, and individual metabolism. The NHS recommends losing 0.5 to 1 kg per week for sustainable results. Fasting works best combined with a balanced diet and exercise, not in isolation.
Is intermittent fasting safe for everyone?
Not necessarily. People with type 2 diabetes, eating disorders, certain medications, pregnant or breastfeeding women, and those with a history of disordered eating should avoid fasting without medical supervision. Always consult your GP before starting any fasting plan, especially if you have health conditions.
What should I eat during my eating window?
Focus on nutritious, whole foods: vegetables, lean proteins, whole grains, and healthy fats. Avoid high-calorie processed foods, sugary drinks, and excessive snacking. Quality matters as much as quantity — eating 1500 kcal of vegetables and protein is more sustainable than 1500 kcal of takeaway food.
How quickly will I lose weight with a fasting plan?
Safe weight loss is typically 0.5 to 1 kg per week. With a 16:8 fasting approach, you might lose 2–4 kg per month if you maintain a calorie deficit. Results vary based on starting weight, age, metabolism, and how strictly you follow the plan. Be patient — sustainable loss beats rapid loss.
Can I combine fasting with prescription weight loss medication?
Potentially, but this requires medical guidance. GLP-1 medications like Mounjaro and Wegovy work best alongside diet and exercise. Combining fasting with prescription medication should only be done under supervision from your GP or prescriber. Do not attempt this without professional assessment.
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.