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 is a body composition device that uses bioelectrical impedance analysis (BIA) to estimate your body fat percentage alongside your weight. Unlike standard scales that only measure total weight in kg or stone, fat scales send a harmless electrical signal through your body to estimate the ratio of fat to muscle. They're increasingly popular in UK households for health monitoring, though their accuracy varies depending on hydration, exercise timing, and the device quality. Understanding how they work—and their limitations—is important for interpreting results as part of your broader healthy weight UK assessment.
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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 Accurate Are Fat Scales in the UK?
Fat scales use bioelectrical impedance analysis (BIA), which measures how easily electrical current flows through your body. Fat conducts electricity differently than muscle, allowing the device to estimate body composition. However, accuracy varies significantly:
- Hydration status affects readings — dehydration makes fat estimates higher
- Exercise timing matters — measurements taken immediately after exercise can be inaccurate
- Device quality varies — budget scales are less reliable than clinical-grade equipment
- Individual factors like age, ethnicity, and fitness level influence accuracy
- BIA is typically accurate within ±3–5% of actual body fat for healthy individuals
For the most reliable assessment, use the same fat scale at the same time of day, under consistent conditions. NHS guidance suggests that waist circumference and BMI remain more reliable indicators of health risk than fat percentage alone. You can calculate your BMI instantly using our free BMI calculator on this page to get a clinically validated health metric alongside any fat scale 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 Scales vs Other UK Health Measurements
While fat scales provide body composition data, they're most useful when combined with other nhs health advice metrics. BMI (Body Mass Index) remains the NHS standard screening tool, though it doesn't distinguish muscle from fat. Waist circumference is another key measurement — men with waist over 102cm (40 inches) and women over 88cm (35 inches) face increased health risk regardless of BMI.
Rather than relying solely on fat scale readings, use multiple indicators: track your weight in kg or stone using our weight converter, monitor your BMI, measure your waist, and assess how your clothes fit and energy levels change. Our free progress tracker helps you log all these metrics over time. For personalised uk health information about what your body composition means for your health, consult your GP, especially if you're considering weight management or have health concerns.
- 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.
Is a fat scale more accurate than BMI?
Not necessarily. Fat scales measure body composition but have a margin of error of ±3–5%. BMI is less precise per individual but provides a clinically validated screening tool. NHS guidance recommends using both alongside waist measurement for a complete picture of health risk. Your GP can advise which metric is most relevant for you.
Can I use a fat scale if I'm pregnant?
No. Fat scales use electrical signals that are not recommended during pregnancy. Pregnant women should discuss safe weight monitoring with their midwife or GP. Standard scales measuring weight in kg or stone are safe to use throughout pregnancy.
How often should I weigh myself on a fat scale?
Once weekly, at the same time of day and under consistent conditions (e.g. morning, before exercise, after using the toilet), gives the most reliable trend data. Daily readings fluctuate due to hydration, food intake, and hormonal changes. Track results over weeks and months rather than worrying about daily variations.
What's a healthy body fat percentage in the UK?
For women: 21–31% is generally considered acceptable; for men: 18–24%. However, healthy ranges vary by age and fitness level. Rather than fixating on a single number, focus on overall health markers including energy levels, fitness improvements, and stable weight within your NHS healthy weight range.
Should I buy an expensive fat scale or a budget one?
Clinical-grade fat scales (£200+) are more accurate than budget models (£30–80), but consistency matters more than cost. If you use the same device under the same conditions regularly, even a budget scale can track trends reliably. For most people, combining a standard scale with our free BMI calculator and weight converter provides sufficient health monitoring.
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.