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
Understanding Fat Weight Scales and Body Composition
A fat weight scale, also called a body composition scale or bioelectrical impedance scale, measures more than just your total weight โ it estimates the percentage of your body that is fat versus muscle and bone. These scales work by sending a small electrical signal through your body to estimate fat distribution. However, accuracy varies significantly, and NHS guidance still emphasises BMI and waist circumference as more reliable health indicators. Understanding what these scales measure, and their limitations, helps you make informed decisions about your weight management and overall health.
10,000+ calculations today ยท NHS-aligned thresholds ยท 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/mยฒ).
While BMI isn't a perfect measure โ it doesn't account for muscle mass, bone density, or fat distribution โ 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 โ 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 Fat Weight Scales Work and Their Limitations
Fat weight scales use bioelectrical impedance analysis (BIA) โ a small electrical current passes through your body to measure resistance, which estimates body fat percentage. However, these scales have important limitations:
- Accuracy depends on hydration level โ dehydration can significantly alter readings
- They cannot distinguish between different types of fat or account for where fat is stored
- Muscle mass, bone density, and fitness level affect readings but are not precisely measured
- Results vary between brands and models โ the same person may get different readings on different scales
- Readings are less accurate for very lean, very obese, or elderly individuals
For reliable health assessment, the NHS recommends combining scales with BMI calculation, waist circumference measurement, and professional health review. Use our free BMI calculator above to check your personal BMI instantly alongside any fat scale reading.
Clinically BackedWeight Loss
No appointments. No waiting rooms. Just care โ 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 โ 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 โ completely free.
Why BMI and Waist Circumference Matter More for UK Health Guidance
The NHS considers BMI and waist circumference more reliable than fat weight scales for assessing health risk. A healthy BMI in the UK is 18.5 to 24.9, though South Asian, Chinese, Black African, and Black Caribbean adults should aim for 18.5 to 22.9 due to higher cardiovascular risk at lower BMI levels. Waist circumference is equally important โ men should aim for under 94cm (37 inches), women under 80cm (31.5 inches). These measurements can be tracked over time more reliably than fat scale readings. If you're exploring weight management options, including lifestyle changes or considering weight loss support, our free weight converter and progress tracker can help you set realistic goals and monitor sustainable progress alongside your GP's guidance.
- 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 โ 5mg โ 7.5mg โ 10mg โ 12.5mg โ 15mg
- GLP-1 receptor agonist
- Up to 15โ17% body weight loss (STEP trials)
- Weekly injection, 5-step dose escalation
- NHS & private prescription available
- Doses: 0.25mg โ 0.5mg โ 1mg โ 1.7mg โ 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 | 15โ22.5% | 12โ17% |
| Key trial | SURMOUNT-1 (2022) | STEP 1 (2021) |
| Max dose | 15 mg weekly | 2.4 mg weekly |
| Escalation period | 20โ32 weeks | 16โ20 weeks |
| Administration | Weekly injection (pen) | Weekly injection (pen) |
| NHS availability | Private prescription only | NHS & private |
| Approx. private cost | ยฃ150โยฃ250/month | ยฃ150โยฃ300/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 โ 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.
Are fat weight scales accurate?
Fat weight scales provide estimates but are not highly accurate. They vary based on hydration, muscle mass, and individual factors. The NHS recommends using BMI and waist circumference as more reliable health indicators. Professional body composition analysis (DEXA scans) is more accurate but expensive.
What's the difference between a fat weight scale and a standard scale?
Standard scales measure total body weight only. Fat weight scales estimate the percentage breakdown between fat, muscle, and bone using bioelectrical impedance. Neither replaces proper health assessment โ your GP can advise on what measurements matter most for your individual health.
Can I rely on fat scale readings to track weight loss?
Fat scales can show trends over time if used consistently under similar conditions (same time of day, hydration level). However, they're not precise enough for week-to-week accuracy. Tracking total weight loss, waist circumference, and how you feel are more reliable indicators of progress.
What should I do if my fat scale reading seems wrong?
Retest under consistent conditions โ same time of day, after using the bathroom, in a similar hydration state. If readings still seem incorrect, check your scale's calibration or try a different scale. Remember that fat scales estimate rather than measure โ variation between devices is normal.
Is body fat percentage more important than BMI for health?
Both matter, but differently. BMI is a population-level screening tool that doesn't distinguish fat from muscle. Body fat percentage is more nuanced but harder to measure accurately at home. Your GP can help determine what's most relevant for your individual health and weight management goals.
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.