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
BMI and Weight Loss Calculator Explained
Your BMI (body mass index) and weight loss goals are directly connected — understanding both helps you set realistic targets and track progress effectively. MyWeightCheck provides free tools to calculate your BMI instantly and explore potential weight loss outcomes based on evidence-based methods. Whether you're checking if you're a healthy weight or considering weight loss options, these calculators give you the personalised data you need to make informed decisions with your GP.
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 BMI and Weight Loss Targets Work Together
BMI is calculated using your weight (kg) divided by your height (m)². The NHS BMI categories are: underweight (below 18.5), healthy weight (18.5–24.9), overweight (25.0–29.9), and obese (30.0 and above). For South Asian, Chinese, Black African, and Black Caribbean adults, the NHS recommends lower thresholds — healthy weight is 18.5–22.9 and overweight starts at 23.0.
Weight loss calculators estimate how much weight you might lose based on calorie deficit or medication type. The NHS recommends losing 0.5–1 kg per week through a combination of reduced-calorie diet and increased physical activity — this translates to a calorie deficit of around 500 kcal daily. Our free BMI calculator above shows your current category instantly, while our GLP-1 weight loss calculator can project potential outcomes if you're considering prescription weight loss medication like Mounjaro or Wegovy.
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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.
BMI Limitations and Complementary Health Measures
While BMI is a useful screening tool, it has important limitations. BMI does not distinguish between muscle and fat — athletes may have a high BMI but low body fat percentage. It also doesn't account for where fat is stored; carrying weight around your waist is a higher health risk than fat distributed elsewhere.
For a more complete picture, also consider your waist circumference. The NHS recommends: men keep waist under 94 cm (37 inches); women under 80 cm (31.5 inches). Use our weight converter to check your weight in different units, and our progress tracker to monitor changes over time alongside your BMI measurements.
- 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.
What's the difference between a BMI calculator and a weight loss calculator?
A BMI calculator shows where your current weight sits within NHS healthy ranges. A weight loss calculator estimates how much weight you might lose over time based on calorie deficit or medication type. Both are useful: BMI shows your starting point, weight loss projection shows your potential destination.
Can I use a weight loss calculator to studied results?
No. Weight loss calculators provide estimates based on average outcomes, but individual results vary significantly depending on your genetics, metabolism, adherence to diet/exercise, medications, and health conditions. Always discuss realistic targets with your GP.
Why do South Asian and Black African adults have different BMI thresholds?
Research shows these populations face higher risk of type 2 diabetes and cardiovascular disease at lower BMI levels. The NHS recommends lower healthy weight thresholds (18.5–22.9) for these groups to better reflect their individual health risk profiles.
Should I use BMI or waist measurement to check my health?
Both are useful. BMI is a quick screening tool, but waist circumference is also important — excess weight around your stomach carries higher health risk. Use both metrics together for a fuller picture of your health. Your GP can interpret both in context of your individual health.
How often should I recalculate my BMI?
You can recalculate whenever your weight changes significantly (every few weeks if you're losing weight). Our free progress tracker helps you log weight changes and see your BMI category update automatically, making it easy to monitor your journey over time.
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.