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 Weight Loss Diet?
A weight loss diet is an eating plan designed to help you consume fewer calories than your body burns, creating a calorie deficit that supports gradual weight reduction. In the UK, the NHS recommends losing weight at a safe rate of 0.5 to 1 kg per week through a combination of dietary changes and increased physical activity. Weight loss isn't just about following a specific diet — it's about sustainable lifestyle changes that work with your individual health needs. Whether you're looking to improve weight management through diet alone or alongside other support like prescription weight loss medication, understanding how diets work is the first step.
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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 Weight Loss Diets Work
Weight loss occurs when you eat fewer calories than your body uses for energy — known as a calorie deficit. The NHS suggests a deficit of approximately 500 kcal per day typically results in losing around 0.5 kg per week. Most weight loss diets work by either reducing portion sizes, cutting specific food groups (like carbohydrates or fats), or increasing meals with higher protein and fibre to keep you feeling fuller longer.
- Low-calorie diet: 1200–1500 kcal per day for women, 1500–1900 kcal per day for men
- Very low-calorie diet (VLCD): Under 800 kcal per day — only recommended under medical supervision
- Low-carbohydrate diet: Reduces carbs to create a deficit; effective short-term but long-term results similar to standard calorie restriction
- Mediterranean diet: Evidence-based approach emphasising whole foods, vegetables, and healthy fats — supports both weight loss and cardiovascular health
- Intermittent fasting: Time-restricted eating (such as 16:8 fasting) — moderate evidence for weight loss when combined with calorie awareness
The best weight loss diet is one you can stick to consistently. Your GP can provide personalised dietary advice or refer you to an NHS dietitian for support.
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.
Weight Loss Diet and Prescription Support
For people with a BMI of 30 or above, or 27 or above with weight-related health conditions, prescription weight loss medication may be considered alongside diet and exercise. GLP-1 weight loss injections like Wegovy (semaglutide) and Mounjaro (tirzepatide) are licensed in the UK and work by helping reduce appetite and food cravings, making it easier to maintain a lower-calorie diet. These medications are prescription-only and require clinical assessment from a GP or licensed prescriber. Our GLP-1 weight loss calculator can help you understand potential results at different doses. Remember, any prescription medication is used alongside — not instead of — dietary changes and physical activity for best results.
- 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's the difference between a weight loss diet and just eating less?
A weight loss diet is a structured eating plan with specific guidelines about what and how much to eat. Simply eating less without a plan may lead to nutrient deficiencies or unsustainable hunger. A proper weight loss diet balances calorie reduction with nutrition, making it more sustainable long-term.
How quickly will I lose weight on a weight loss diet?
The NHS recommends losing 0.5 to 1 kg per week for safe, sustainable weight loss. This typically requires a calorie deficit of around 500 kcal per day. Faster weight loss is possible but increases the risk of muscle loss and nutrient deficiencies — only pursue rapid loss under medical supervision.
Do I need to follow a specific weight loss diet, or can I create my own?
You can create your own calorie-deficit plan if you understand nutrition, but working with a GP or registered dietitian is safer and more effective. They can assess your individual health needs, recommend appropriate calorie targets, and help you avoid nutrient deficiencies. NHS Tier 1 weight management services also offer free guidance.
Can weight loss diets be combined with weight loss injections?
Yes. Prescription weight loss medications like Wegovy and Mounjaro work best alongside a reduced-calorie diet and increased physical activity. These medications help reduce appetite, making it easier to maintain dietary changes — they're not a replacement for diet and exercise.
What should I do if a weight loss diet isn't working?
If you've been following a diet consistently for several weeks without results, speak to your GP. They can check for underlying health issues (thyroid problems, metabolic factors) and discuss alternative approaches, including prescription weight loss support or referral to specialist weight management services.
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.