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
What Is a 4:3 Weight Loss Plan?
The 4:3 weight loss plan is an intermittent eating pattern where you eat normally for four days and restrict calories for three consecutive days each week. It's one of several structured approaches to weight management used in the UK alongside NHS guidelines. The pattern aims to create a weekly calorie deficit while allowing flexibility on eating days. Success depends on maintaining a calorie deficit overall, which typically requires around 500 kcal below your daily needs for sustainable weight loss of 0.5 to 1 kg per week — the rate the NHS recommends.
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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 the 4:3 Plan Works for Weight Loss
The 4:3 plan follows a simple weekly structure: four days of normal eating followed by three consecutive days of reduced-calorie intake, typically 500–800 kcal per day. On restriction days, you eat roughly one-third of your normal intake, while "normal" days allow regular meals without strict calorie counting (though some awareness is still needed to create overall deficit).
The mechanism for weight loss is straightforward: if your daily calorie needs are 2,000 kcal, eating normally four days (8,000 kcal) plus restricted three days (1,500–2,400 kcal) creates a weekly total of 9,500–10,400 kcal against a balanced week of 14,000 kcal — a deficit of 3,600–4,500 kcal, roughly 0.5–0.65 kg loss per week.
This approach appeals because it avoids daily restriction fatigue. You can use our free GLP-1 weight loss calculator to compare projected losses with different methods, and our weight converter to track progress in stone and pounds.
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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.
4:3 Plan vs Other Weight Loss Approaches
The 4:3 plan differs from alternatives like continuous calorie restriction, 5:2 intermittent fasting, and prescription weight management injections (such as GLP-1 medications like Wegovy or Mounjaro). Continuous restriction requires discipline daily; 5:2 uses two restriction days weekly instead of three; injections work through appetite reduction mechanisms and may suit those with a BMI of 30+ or 27+ with weight-related health conditions.
Your GP can help assess which approach suits your lifestyle and health. Calculate your BMI using our free tool to understand your current health category, then discuss options with your healthcare provider.
- 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.
Is the 4:3 weight loss plan safe to follow?
The 4:3 plan can be safe for most adults when creating a moderate calorie deficit (around 500 kcal daily). The NHS recommends losing 0.5–1 kg weekly. However, it's not suitable for children, pregnant women, or those with eating disorders. Always discuss any new eating plan with your GP first, especially if you have diabetes or take medications.
How much weight can I expect to lose on the 4:3 plan?
Average weight loss depends on your starting weight, age, activity level, and how strictly you follow restriction days. Most people lose 0.5–1 kg per week with a consistent 500 kcal daily deficit. Over 12 weeks, this equals 6–12 kg, though individual results vary significantly. Track your progress using our free progress tracker.
What's the difference between the 4:3 plan and 5:2 fasting?
The 4:3 plan restricts calories three days weekly; 5:2 fasting uses two non-consecutive restriction days. 5:2 may be easier for some people as it offers more non-restriction days. The 4:3 plan groups restriction days together, which some find more structured. Both create similar overall weekly calorie deficits if calories are equal.
Can I combine the 4:3 plan with prescription weight loss injections?
Prescription weight loss medications like Wegovy (semaglutide) or Mounjaro (tirzepatide) should be used as prescribed by your healthcare provider — typically alongside a reduced-calorie diet and increased physical activity. Combining structured eating plans like 4:3 with medication requires GP guidance. Never combine medications or eating plans without medical approval.
How does my BMI relate to choosing a weight loss method?
Your BMI helps determine which approaches are recommended. The NHS suggests lifestyle changes first for BMI 25–29.9. For BMI 30+, or 27+ with weight-related conditions, prescription weight loss medications may be considered. Calculate your BMI above to understand your health category, then discuss options with your GP.
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.