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
Free Weight Loss Calculator for UK Adults
A free weight loss calculator helps you estimate realistic weight management outcomes based on your current weight, height, and chosen approach. Whether you're considering prescription weight loss medication, lifestyle changes, or a combination of both, understanding potential results can help you set achievable health goals. Our calculator uses evidence-based data from clinical trials and NHS weight management guidelines to give you personalised projections. Individual results vary significantly, but having a clear picture of what's possible can motivate sustainable progress in your weight management journey.
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 Our Weight Loss Calculator Works
Our free weight loss calculator uses your personal health data to project realistic weight loss outcomes across different timeframes. It factors in your current BMI, age, and the method you choose—whether that's lifestyle changes alone, GLP-1 medication such as Mounjaro or Wegovy, or a combination approach.
The calculator is based on clinical trial data: clinical trials with Wegovy showed average weight loss of approximately 14.9% of body weight, while Mounjaro trials demonstrated average losses of 15–21% depending on dose. However, actual results depend on many factors including adherence, diet quality, physical activity, genetics, and individual metabolism.
Our calculator also accounts for NHS weight management guidance, which recommends losing 0.5–1 kg per week for sustainable results. This helps you understand whether your projected timeline is realistic and healthy. Remember: prescription weight loss medication is prescription-only and requires a clinical assessment from a licensed prescriber before you can access it.
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.
Use the Calculator to Set Your Health Goals
Start by entering your current weight in kg or stone, your height, and your target weight or goal BMI. The calculator will instantly show you estimated weight loss timelines and potential health improvements. Many people find this process motivating because it transforms abstract goals ("lose weight") into concrete, achievable numbers.
Try the GLP-1 weight loss calculator on this page to compare projections across different prescription options. You can also use our BMI calculator to understand where you currently sit on the NHS healthy weight scale, and our weight converter to switch between metric and imperial measurements.
Once you start your weight loss journey, our free progress tracker lets you log weekly weigh-ins and visualise your progress over time—this can be incredibly motivating and helps you spot patterns in your 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.
Is a free weight loss calculator accurate?
A weight loss calculator provides estimates based on average outcomes from clinical trials and research. Individual results vary significantly due to genetics, medication adherence, diet quality, exercise levels, and metabolism. Use the calculator as a planning tool, not a assures. Your actual results may be faster or slower—always monitor your progress and discuss results with your GP or prescriber.
Can I use a weight loss calculator without medication?
Yes. The calculator can project results from lifestyle changes alone—diet and exercise combined typically result in 0.5–1 kg per week loss through a calorie deficit. It can also show how prescription weight loss medication might accelerate results. Many people use a combination approach for best outcomes.
What's the difference between Mounjaro and Wegovy in the calculator?
Mounjaro (tirzepatide) is a dual GIP/GLP-1 agonist with average weight loss of 15–21% in clinical trials, depending on dose. Wegovy (semaglutide) is a GLP-1 agonist with average weight loss around 14.9% at maximum dose. Both are prescription-only and results vary individually. The calculator helps you compare projected outcomes, but eligibility and suitability must be assessed by a prescriber.
How do I know if I'm eligible for prescription weight loss treatment?
In the UK, you may be eligible for prescription weight loss medication if you have a BMI of 30 or above, or 27–29.9 with weight-related health conditions such as type 2 diabetes, high blood pressure, or sleep apnoea. Use our free BMI calculator to check your current BMI, then speak to your GP or a licensed prescriber about whether medication is appropriate for you.
Should I use the calculator before or after starting weight loss medication?
Use it both ways. Before starting, use the calculator to set realistic expectations and plan your journey. After starting, track your actual progress using our progress tracker and compare it to your initial projections. This helps you stay motivated and ensures you're on track. If your results differ significantly from projections, discuss this with your prescriber—adjustments may help.
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.