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
How Calorie Deficit Connects to Weight Loss
A calorie deficit is the key to sustainable weight loss. When you consume fewer calories than your body burns, you create the conditions for fat loss. The NHS recommends losing weight at a steady rate of 0.5 to 1 kg per week, which typically requires a calorie deficit of around 500 kcal per day. Understanding how your calorie intake connects to weight loss helps you set realistic goals and track progress effectively. MyWeightCheck provides tools to help you calculate your BMI, track weight changes, and understand your personal healthy weight range for your height and age.
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.
Understanding the Calorie-to-Weight-Loss Relationship
The relationship between calorie deficit and weight loss is straightforward but varies between individuals based on metabolism, age, activity level, and genetics.
- 500 kcal daily deficit: Results in approximately 0.5 kg (1 lb) weight loss per week
- 1000 kcal daily deficit: Results in approximately 1 kg (2 lbs) weight loss per week — only recommended under medical supervision
- Baseline calculation: Most adults need 1800–2500 kcal daily to maintain current weight; this varies significantly
The NHS emphasises that sustainable weight management in the UK involves both dietary changes and increased physical activity. gradual weight management (more than 1.5 kg per week) increases the risk of muscle loss, nutritional deficiencies, and may be harder to maintain long-term. Using our free BMI calculator helps you identify your current weight category and healthy weight range for your height, providing context for realistic loss targets.
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.
Prescription Weight Loss Support and Realistic Projections
For many people in the UK, prescription weight loss medication may be recommended alongside calorie deficit strategies. Medications such as GLP-1 injections may help reduce appetite and support feeling fuller after meals, potentially making a calorie deficit easier to maintain.
Clinical trials have shown that people using GLP-1 medications alongside lifestyle changes lose an average of 15–21% of their body weight — though individual results vary significantly. Our GLP-1 weight loss calculator can help you estimate potential outcomes at different doses, while our free progress tracker allows you to log your weight loss journey and monitor changes over time. Always consult your GP to discuss whether prescription support is appropriate for you and your specific health circumstances.
- 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.
How many calories must I cut to lose 1 kg per week?
To lose approximately 1 kg (2.2 lbs) per week, you typically need a calorie deficit of around 1000 kcal per day. However, the NHS recommends the safer target of 0.5–1 kg per week, requiring a 500 kcal daily deficit. Individual needs vary based on age, metabolism, and current weight — your GP can provide personalised guidance.
Is gradual weight management from a large calorie deficit safe?
gradual weight management (more than 1.5 kg per week) without medical supervision increases risks including muscle loss, nutrient deficiencies, fatigue, and gallstones. The NHS recommends gradual, sustainable loss of 0.5–1 kg weekly. If considering a very low calorie diet (under 800 kcal daily), this must only be done under medical supervision.
Does everyone lose weight at the same rate with the same calorie deficit?
No. Weight loss varies between individuals due to differences in metabolism, age, muscle mass, hormones, genetics, and medical conditions. Two people with identical calorie deficits may lose weight at different rates. This is why personalised health assessment from your GP is valuable.
Can I use a calorie calculator alongside weight loss medication like Wegovy?
Yes. Prescription weight loss medications like Wegovy (semaglutide) are designed to be used alongside dietary changes and increased activity — not instead of them. Your prescriber will advise you on calorie targets that work safely with your medication. Try our GLP-1 weight loss calculator to explore potential outcomes.
How does BMI relate to calorie deficit and weight loss targets?
Your BMI helps determine your current weight category and healthy weight range for your height. Use our free BMI calculator to find your range, then work backwards to set realistic weight loss targets. For example, if your healthy range is 55–75 kg and you're currently 90 kg, losing 15–20 kg would bring you into that range over several months.
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.