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 — What to Expect
A weight loss predictor helps you understand realistic outcomes based on your current weight, height, and chosen weight management approach. Whether you're considering prescription weight loss medication through the NHS, exploring GLP-1 injections privately, or planning a dietary approach, knowing what to expect helps you set achievable goals. Individual results vary significantly, but evidence-based projections can guide your expectations.
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
A weight loss predictor calculates potential weight loss by considering your starting weight, age, gender, activity level, and chosen intervention. For prescription weight loss medications like Wegovy (semaglutide) and Mounjaro (tirzepatide), predictors use clinical trial data to estimate outcomes.
- Wegovy clinical trials (STEP studies) showed average weight loss of approximately 15% of body weight over 68 weeks
- Mounjaro trials (SURMOUNT studies) demonstrated average loss of 15–21% depending on dose
- Lifestyle-only weight loss typically results in 0.5–1 kg per week with a sustained calorie deficit
- Combination approaches (medication plus diet and exercise) often produce the best results
Our GLP-1 weight loss calculator on this page uses established clinical data to project potential outcomes. Results depend on adherence, lifestyle factors, and individual metabolism — no two people respond identically.
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.
Key Factors That Affect Weight Loss Predictions
Starting weight: People with higher starting weights often lose more weight initially, though percentage loss may be similar. Age and gender: Metabolism varies, affecting loss rates. Medication compliance: Consistent use of prescribed GLP-1 medication yields better results than inconsistent use.
Lifestyle changes: Weight management through prescription medication works best alongside reduced-calorie diet and increased physical activity — medication alone is less effective. Health conditions: Thyroid disorders, PCOS, and diabetes may affect outcomes. Your GP can provide personalised guidance on what realistic expectations look like for your specific situation.
- 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.
Can a weight loss predictor tell me exactly how much weight I'll lose?
No. Predictors provide estimates based on averages from clinical trials, but individual results vary significantly. Factors like genetics, metabolism, adherence to medication or diet, and overall health all influence actual outcomes. Use a predictor as a guide, not a assures.
Are weight loss predictions the same for Wegovy and Mounjaro?
Both are GLP-1-based medications, but they work slightly differently. Mounjaro is a dual GIP/GLP-1 agonist, while Wegovy is GLP-1 only. Clinical data suggests Mounjaro may produce slightly higher average weight loss (15–21% vs ~15% for Wegovy), but individual results vary considerably.
What if I lose weight slower than the predictor suggests?
Slower weight loss is still meaningful. Even 5–10% body weight reduction delivers significant health benefits including improved blood pressure, better blood sugar control, and reduced joint strain. If progress is slower than expected, discuss with your GP — dose adjustments or lifestyle modifications may help.
Does the predictor account for NHS weight management programmes?
NHS weight loss prediction depends on your tier of service. Tier 1 self-help typically yields 0.5–1 kg per week. Tier 3 specialist services using medication may produce higher losses. Your GP can discuss realistic timelines for NHS pathways in your area.
How do I use a weight loss predictor with the MyWeightCheck tools?
Start by calculating your current BMI using our free BMI calculator. Then use our GLP-1 weight loss calculator to estimate outcomes with prescription medication, or track your actual progress with our progress tracker as you work toward your goal 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.