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
What Is a Fat Scale and How Does It Work?
A fat scale, also called a body composition scale or bioelectrical impedance scale, is a weighing device that estimates your body fat percentage alongside your total weight. Unlike a standard bathroom scale, fat scales use a weak electrical current to measure body composition — typically distinguishing between fat mass, muscle mass, water weight, and bone density. They're becoming increasingly popular in UK homes as part of a more comprehensive approach to health monitoring, though they have important limitations worth understanding.
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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 Body Composition Scales Work
Fat scales use bioelectrical impedance analysis (BIA) to estimate body composition. A small, painless electrical current passes through your body — typically via metal contacts on your feet or hands. Muscle tissue conducts electricity differently than fat tissue, allowing the scale to calculate the ratio between them.
- The scale sends a signal through your body and measures resistance
- Based on your height, weight, age, and sex, it calculates estimated fat percentage
- Results appear instantly on a digital display, often with other metrics like muscle mass and water percentage
However, accuracy depends heavily on factors like hydration level, recent exercise, food intake, and skin contact quality. A reading can vary by 5–10% depending on these variables. For this reason, fat scales work best for tracking trends over weeks and months rather than relying on single readings.
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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.
Fat Scale vs Standard Scale: Key Differences
A standard bathroom scale only measures total weight — it cannot distinguish between fat and muscle. This is why two people at the same weight can look completely different: one may have high muscle mass, the other high fat percentage. A fat scale provides additional insight into body composition, which is useful for understanding whether weight changes are due to fat loss or muscle gain.
For UK health guidance, the NHS emphasizes BMI alongside waist circumference as primary screening tools. Use our free BMI calculator above to check your BMI instantly. A fat scale can be a useful supplementary tool when combined with BMI and waist measurement, but should not replace them as your main health indicator.
- 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.
Are fat scales accurate?
Fat scales provide reasonable estimates for tracking trends but are not perfectly accurate for individual readings. Accuracy varies by 5–10% depending on hydration, recent exercise, food intake, and body type. They work best for monitoring changes over weeks, not for single precise measurements.
What is a healthy body fat percentage?
For women, healthy body fat ranges from 14–24%, with 25–31% being acceptable. For men, 6–13% is athletic, 14–17% is fitness, and 18–24% is acceptable. These ranges vary by age and individual health — consult your GP for personalised guidance.
How often should I weigh myself on a fat scale?
Weighing once or twice weekly at the same time of day (ideally morning, after using the toilet) gives the most reliable trend data. Avoid daily weighing, as natural fluid fluctuations can cause readings to vary significantly without actual fat loss or gain.
Can a fat scale replace BMI measurements?
No. Whilst a fat scale is useful for assessing body composition, the NHS recommends using BMI as a primary screening tool alongside waist circumference. Try our weight converter and BMI calculator above for a complete health picture tailored to UK health standards.
What factors affect fat scale readings?
Hydration status, recent exercise, meal timing, skin contact quality, menstrual cycle, and swelling all affect readings. For consistent results, weigh yourself at the same time daily, well-hydrated, before eating, and after using the toilet.
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.