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 Many Calories Do You Need For Weight Loss?
To lose weight sustainably, you need to consume fewer calories than your body burns — creating a calorie deficit. The NHS recommends losing weight at a rate of 0.5 to 1 kg per week, which typically requires a deficit of around 500 calories per day. However, the exact number of calories you need depends on your current weight, age, sex, activity level, and metabolism. This guide explains how to calculate your personal calorie needs and combine dietary changes with other weight management strategies for the best results.
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 Your Calorie Deficit For Weight Loss
A calorie deficit occurs when you consume fewer calories than your body burns through daily activities and metabolism. To lose approximately 0.5 kg per week (a safe, sustainable rate recommended by the NHS), you generally need a deficit of around 500 calories per day. For 1 kg per week loss, you would need roughly a 1,000 calorie daily deficit — though this is more aggressive and usually requires professional support.
- Your Basal Metabolic Rate (BMR) — calories your body burns at rest — varies based on age, sex, weight, and muscle mass
- Adding physical activity increases your total daily energy expenditure, making a deficit easier to achieve without extreme dietary restriction
- Very low calorie diets (under 800 kcal/day) should only be followed under medical supervision and are typically only recommended in specialist weight management services
- A moderate deficit of 500 kcal/day is more sustainable than aggressive restriction and better preserves muscle mass
You can use online calculators to estimate your daily calorie needs, then subtract 500 to find a sustainable deficit for gradual weight 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.
Combining Calorie Deficit With Other Weight Loss Approaches
Calorie restriction works best alongside increased physical activity and dietary behaviour change. Evidence suggests that combining a modest calorie deficit with regular exercise and structured eating habits produces better long-term results than calorie counting alone.
- For adults with a BMI over 25, the NHS Weight Loss Plan offers free digital support combining calorie guidance with behaviour change techniques
- Prescription weight loss medications like GLP-1 injections may support weight management by reducing appetite — used alongside a reduced-calorie diet and increased physical activity
- Our free BMI calculator can help you assess where you currently stand on the healthy weight scale for your height
- Tracking your progress using tools like our free progress tracker helps maintain motivation and identify what's working for you
- 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 500 calorie and 1000 calorie daily deficit?
A 500 calorie deficit typically results in losing about 0.5 kg per week — the NHS recommended safe rate. A 1,000 calorie deficit would aim for 1 kg per week but increases the risk of muscle loss, nutrient deficiency, and fatigue. Slower, sustainable loss is generally preferable unless under medical supervision.
How do I calculate my personal calorie needs for weight loss?
Start by estimating your Total Daily Energy Expenditure (TDEE) using online calculators or apps — these account for your age, sex, weight, height, and activity level. Once you know your TDEE, subtract 500 calories to find a sustainable deficit. If unsure, your GP or a registered dietitian can provide personalised guidance.
Can I lose weight without counting calories?
Yes. Many people lose weight effectively by focusing on eating whole foods, reducing portion sizes, increasing protein and fibre intake, and being more physically active — without strictly counting calories. However, some calorie awareness can help ensure you're maintaining a deficit, especially if progress plateaus.
Is weight loss medication like Wegovy an alternative to calorie deficit?
Prescription weight loss medications like Wegovy (semaglutide) are not replacements for calorie deficit — they work alongside dietary changes and activity. These medications may help reduce appetite, making it easier to maintain a deficit. They require clinical assessment and a prescription from a licensed healthcare professional.
What's a realistic timeframe for losing weight through calorie deficit alone?
At a safe deficit of 500 kcal/day (0.5 kg per week), you might lose approximately 2 kg per month or 24 kg per year. Results vary based on individual metabolism, adherence, and other factors. Most people see meaningful health benefits after losing just 5–10% of their body weight.
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.