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 Predictor Calculator — How Much Weight Can You Lose?
A weight loss predictor calculator helps you estimate realistic weight loss outcomes based on your current health, lifestyle, and whether you're considering prescription weight management options like GLP-1 medications. Understanding what's achievable is crucial for setting sustainable goals and staying motivated throughout your weight management journey in the UK.
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 Weight Loss Predictors Work
Weight loss predictors use evidence-based calculations to estimate potential outcomes. They typically account for your current weight, height, age, activity level, and dietary intake to project weight loss over specific timeframes. For prescription weight loss medications, predictors factor in clinical trial data—such as results from the STEP trials for Wegovy (semaglutide), which showed participants lost an average of approximately 15% body weight over 68 weeks.
Our free GLP-1 weight loss calculator helps you explore potential weight loss at different medication doses. It's important to remember that individual results vary significantly based on adherence, diet, exercise, metabolism, and other health factors. A realistic approach combines medication with a reduced-calorie diet and increased physical activity—this is how results were achieved in clinical trials.
- Calculate projections at 12, 24, and 52 weeks
- Compare outcomes across different GLP-1 doses
- Factor in lifestyle changes alongside medication
- Set achievable milestones
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.
NHS Weight Loss Guidance and Realistic Expectations
The NHS recommends losing weight at a rate of 0.5 to 1 kg per week for sustainable, healthy results. This translates to a calorie deficit of approximately 500 kcal per day. Faster weight loss is possible with medical support—clinical trials of GLP-1 medications showed greater loss—but requires monitoring.
Even modest weight loss of 5–10% of your body weight can deliver meaningful health improvements: lower blood pressure, improved blood sugar control, reduced joint pain, and decreased cardiovascular risk. Use our free BMI calculator alongside a weight loss predictor to track where you stand relative to NHS healthy weight thresholds. If you're considering prescription weight loss medication through the NHS or privately, your prescriber will discuss realistic expectations tailored to your individual 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 accurate is a weight loss predictor calculator?
Weight loss predictors provide evidence-based estimates based on clinical data, but individual results vary. Factors like metabolism, adherence to diet and exercise, sleep quality, stress, and medical conditions all affect real-world outcomes. A predictor is a useful guide, not a assures. Always consult your GP for personalised advice.
Can weight loss medication like Wegovy or Mounjaro assures the weight loss shown in predictors?
Clinical trials showed average weight loss of 15–21% body weight with GLP-1 medications, but individual results vary significantly. These medications work best alongside reduced-calorie diet and increased physical activity. Results depend on your adherence, metabolism, and overall lifestyle. A prescriber will assess what's realistic for you.
What's the difference between weight loss from diet alone versus with medication?
Diet alone typically achieves 0.5–1 kg per week loss if you maintain a 500 kcal daily deficit. GLP-1 medications may support faster loss—clinical trials showed 15–clinically studied weight loss over 68 weeks—by reducing appetite and supporting fuller feelings. Both approaches work best combined with exercise. Results vary between individuals.
How does the NHS approach weight loss prediction?
The NHS recommends losing 0.5–1 kg weekly for sustainable results. They assess your BMI, health conditions, and lifestyle to recommend tier-appropriate support—from digital tools and lifestyle programmes to specialist weight management services where prescription medication may be considered. Your GP can discuss realistic timescales for your situation.
Should I use a weight loss calculator if I'm considering prescription weight loss treatment?
Yes. A weight loss calculator helps you understand realistic expectations before consulting your GP or a prescriber. It demonstrates you've researched options and are motivated. However, any decision about prescription medication must follow a clinical assessment with a licensed prescriber—calculators are educational tools, not medical advice.
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.