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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Fasting Plan for Weight Loss — What Works in the UK
Intermittent fasting can support weight loss when combined with healthy eating habits, but it's just one approach to managing your weight. In the UK, various fasting methods are used alongside lifestyle changes, and for some adults, prescription weight management medication may also be an option. This guide explains different fasting plans, how they work, NHS weight loss guidance, and when prescription treatments like GLP-1 injections might be suitable. Everyone's weight management journey is different, so understanding all available options — from dietary approaches to medication — helps you make informed decisions with 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.
Fasting Methods and How They Work for Weight Loss
Several fasting approaches are used for weight management in the UK. Intermittent fasting (16:8) involves eating within an 8-hour window and fasting for 16 hours — evidence suggests this can support modest weight loss. The 5:2 diet restricts calories to 500–600 kcal on two non-consecutive days per week. Time-restricted eating limits eating to specific hours, potentially reducing overall calorie intake. The NHS recommends losing weight at a rate of 0.5 to 1 kg per week for sustainable results alongside increased physical activity.
Fasting works mainly by creating a calorie deficit — you consume fewer calories overall. It doesn't change metabolism in the way some claim. Research shows fasting approaches produce similar weight loss to standard calorie restriction when total food intake is matched. Success depends on consistency, finding an approach you can sustain, and combining it with nutritious foods during eating windows. For some people, fasting fits their lifestyle; for others, regular meal patterns work better. Use our free BMI calculator to track where you stand, and remember that sustainable weight loss involves both dietary changes and increased physical activity.
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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.
Prescription Weight Management Options in the UK
For adults who need additional support, the NHS and private providers offer prescription weight management medication. Mounjaro (tirzepatide), Wegovy (semaglutide), and Saxenda (liraglutide) are UK-licensed GLP-1 and GIP/GLP-1 medications that may help reduce appetite and support weight loss alongside lifestyle changes. These are prescription-only and require a clinical assessment to determine eligibility.
NHS eligibility: You may qualify if your BMI is 30 or above, or 27 or above with weight-related health conditions (type 2 diabetes, high blood pressure, sleep apnoea). Private access: Available through UK-licensed prescribers without NHS referral, though costs apply. Our GLP-1 weight loss calculator can help you explore potential outcomes at different doses. Whether you choose fasting, medication, or a combination approach, speaking with your GP about your weight management goals is the best first step.
- 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 intermittent fasting speed up weight loss compared to regular dieting?
No — research shows intermittent fasting produces similar weight loss to standard calorie restriction when total calories are matched. Success depends on consistency and finding an eating pattern you can sustain long-term, not the fasting method itself.
Can I combine fasting with prescription weight loss medication?
This depends on the specific medication and your individual health. Always discuss any combination of fasting and medication with your GP or prescriber, as some medications may need adjustment alongside dietary changes.
Is fasting suitable for everyone trying to lose weight?
No — fasting isn't suitable during pregnancy, breastfeeding, or for people with certain medical conditions (eating disorders, severe diabetes complications, or certain medications). Your GP can advise whether fasting is appropriate for you.
How do I find out if I'm eligible for prescription weight loss treatment in the UK?
Start by speaking with your GP about your weight management goals. They can assess your BMI, health conditions, and whether referral to NHS specialist services or private prescription options might be suitable.
What's the difference between NHS weight loss support and fasting plans?
NHS weight management services (tier 1–4) include behaviour change programmes, specialist support, and prescription medication. Fasting is a dietary approach you can try independently. Many people combine both — fasting for structure, and medical support if needed.
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.