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 Calculation: How to Estimate Your Results
Weight loss calculation helps you set realistic goals and track progress towards a healthier weight. Understanding how much weight you might lose depends on several factors including your current weight, calorie deficit, activity level, and whether you're using prescription medication. Whether you're considering lifestyle changes or exploring prescription weight loss options like Mounjaro or Wegovy, calculating your potential results gives you a clear target. Use our free BMI calculator and GLP-1 weight loss calculator to personalise your projections based on your individual circumstances.
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 to Calculate Weight Loss from Calorie Deficit
The most straightforward weight loss calculation is based on calorie deficit. A deficit of approximately 500 kcal per day typically results in losing around 0.5 kg (1 lb) per week. The NHS recommends losing weight at a rate of 0.5 to 1 kg per week for sustainable, long-term results.
- Moderate deficit (500 kcal/day): ~0.5 kg weekly loss
- Larger deficit (1000 kcal/day): ~1 kg weekly loss (requires careful monitoring)
- Very low calorie diet (under 800 kcal/day): Only under medical supervision
To calculate your personal calorie target, start with your estimated daily energy expenditure (which varies by age, sex, height, weight, and activity level), then subtract your target deficit. Track progress using our free progress tracker to monitor weekly losses and adjust your approach if needed.
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.
Weight Loss with Prescription Medication
GLP-1 medications like Wegovy (semaglutide) and Mounjaro (tirzepatide) can significantly enhance weight loss calculation when prescribed as part of a structured weight management programme. Clinical trial data shows Wegovy users lost an average of approximately 14.9% of their body weight over 68 weeks, while Mounjaro users achieved around 15–21% loss depending on dose — though individual results vary considerably.
Both medications are prescription-only and require clinical assessment. They work alongside calorie reduction and increased physical activity — not as a replacement. Our GLP-1 weight loss calculator helps estimate potential results at different doses, but a prescriber must confirm suitability for your individual health profile.
- 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 how much weight I'll lose in a month?
Multiply your expected weekly loss by 4. For example, with a 500 kcal daily deficit (0.5 kg per week), you'd expect approximately 2 kg loss monthly. However, weight loss is not always linear — some weeks you'll lose more, others less. This is normal and doesn't mean your approach isn't working.
What's a realistic weight loss target in kg per week?
The NHS recommends 0.5 to 1 kg per week for sustainable loss. Faster loss is possible with medical support but increases the risk of muscle loss and nutrient deficiency. Very gradual weight management (over 1.5 kg weekly) should only be attempted under healthcare professional supervision.
Can I use BMI change to calculate weight loss progress?
Yes. Use our free BMI calculator to check your BMI now, then recalculate it after losing weight. A BMI reduction of 1–2 points per month indicates healthy progress. For example, moving from BMI 32 to BMI 31 reflects meaningful progress even if the scale weight change seems small.
How does Wegovy or Mounjaro change weight loss calculation?
Prescription GLP-1 medications like Wegovy can enhance calorie deficit effectiveness, but the basic principle remains the same: weight loss requires a calorie deficit. Clinical trials show average losses of 15–21% body weight, but results vary individually. A prescriber assesses whether these medications suit your health circumstances.
Should I weigh myself daily or weekly for weight loss calculation?
Weekly weighing provides more reliable data for calculating progress. Daily weight fluctuates due to water retention, food intake, and hormones — making daily tracking misleading. Choose the same day and time each week (morning after using the toilet) for consistency, and track trends over months rather than reacting to single-week changes.
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.