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
Weight Loss Calculator by Calories — How It Works
A weight loss calculator by calories helps you understand how much weight you might lose based on your daily calorie deficit. The principle is straightforward: creating a calorie deficit of around 500 kcal per day typically results in losing approximately 0.5 kg (1 lb) per week, according to NHS guidance. This makes calorie-based calculation one of the most practical ways to plan sustainable weight management in the UK. Combined with our free BMI calculator, you can track both your current weight category and your projected progress toward a healthier range.
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.
How Calorie Deficit Creates Weight Loss
A calorie deficit is the foundation of weight loss. When you consume fewer calories than your body uses daily (your total daily energy expenditure or TDEE), your body burns stored fat for energy, resulting in weight loss. The NHS recommends a moderate deficit of 500–600 kcal per day for safe, sustainable loss.
- 500 kcal/day deficit: approximately 0.5 kg per week loss
- 1000 kcal/day deficit: approximately 1 kg per week loss (requires careful monitoring)
- Individual factors affect results: age, metabolism, muscle mass, physical activity level, and genetics all influence actual weight loss
Losing more than 1–1.5 kg per week without medical support is not recommended, as rapid loss can mean losing muscle alongside fat. Our free weight loss calculator can help you estimate realistic timelines based on your personal calorie deficit.
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.
Calorie Counting vs. Prescription Weight Management
Calorie deficit is effective for many people, but it requires sustained effort and discipline. Some individuals find that prescription weight loss medication—alongside calorie reduction and increased physical activity—helps them achieve better results. GLP-1 weight loss medications like Mounjaro and Wegovy are prescription-only options available in the UK that may support appetite control and portion management, making a calorie deficit easier to maintain.
These medications require a clinical assessment and are not suitable for everyone. Your GP or a licensed prescriber can assess whether prescription weight management is appropriate for you. Use our GLP-1 weight loss calculator to understand how these medications might fit into your weight management plan—alongside the dietary changes that remain essential for success.
- 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 do I calculate my daily calorie needs?
Your total daily energy expenditure (TDEE) depends on your age, weight, height, sex, and activity level. Online TDEE calculators use the Mifflin-St Jeor equation to estimate this. A rough guide: multiply your body weight in kg by 30 for a moderately active person, then adjust for your actual activity level. Your GP or a registered dietitian can provide personalised guidance.
Is 500 calories per day a safe deficit?
Yes, according to NHS guidance, a deficit of 500 kcal per day is safe and sustainable for most adults, creating approximately 0.5 kg weight loss per week. This gradual approach is more likely to result in lasting change than rapid loss. Never go below 1200 kcal/day without medical supervision.
Can I use calorie counting with weight loss injections?
Yes. Prescription weight loss medications like Mounjaro and Wegovy work best when combined with a reduced-calorie diet and increased physical activity. Calorie awareness remains important—the medication helps manage appetite, making it easier to maintain your deficit. Always follow your prescriber's guidance.
What if I'm not losing weight despite a calorie deficit?
Several factors can slow loss: underestimating food intake, metabolic adaptation, insufficient sleep, high stress, or underlying health conditions like thyroid disorder. If progress stalls after 4–6 weeks, speak to your GP. They can investigate and may refer you to specialist weight management services available through the NHS.
How long does it take to see weight loss results?
Most people see measurable changes within 2–4 weeks of maintaining a calorie deficit, though initial loss includes water weight. Sustainable fat loss becomes apparent after 4–6 weeks. Progress varies by individual. Use our free progress tracker to log weekly weigh-ins and identify trends beyond daily fluctuations.
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.