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
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How to Calculate Weight Difference in the UK
Calculating your weight difference is one of the most practical ways to track progress, whether you're monitoring a health condition or managing your weight. In the UK, we typically measure weight in stone and pounds alongside kilograms, which can make tracking weight change confusing across different units. This guide explains how to calculate weight difference accurately using UK measurements and shows you how to interpret those changes within NHS health guidelines.
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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 to Calculate Weight Difference Across Units
To calculate your weight difference, simply subtract your starting weight from your current weight. The result is your weight change — whether gain or loss.
If using kilograms: Current weight (kg) minus starting weight (kg) = weight difference (kg).
If using stone and pounds: Convert both your starting and current weight to the same unit first, then subtract.
For example, if you weighed 85 kg and now weigh 78 kg, your weight difference is 7 kg loss. Using our free weight converter, this equals approximately 1 stone (14 lbs) of weight loss.
To convert between units: use the standard conversion where 1 stone = 6.35029 kg, or 1 kg = 2.20462 lbs. This ensures your weight difference calculations are consistent whether tracking in metric or imperial.
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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.
UK Health Context for Weight Change
The NHS recommends losing weight at a rate of 0.5 to 1 kg (1 to 2 lbs) per week for sustainable results. This means a healthy weekly weight difference should fall within this range.
Understanding your weight difference also helps you assess whether your current approach is working. If your weight difference over several weeks is significantly faster than 1 kg per week without medical supervision, you may be losing muscle alongside fat. Conversely, if you're not seeing any weight difference after weeks of effort, your GP can help assess whether underlying health factors are involved.
Use our free BMI calculator to see how your weight difference translates to changes in your BMI category, and track long-term progress with our progress tracker to spot trends beyond single weekly 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 is a healthy weight difference per week in the UK?
The NHS recommends losing no more than 0.5 to 1 kg (1 to 2 lbs) per week. This rate helps preserve muscle mass and supports sustainable, long-term weight management. Faster weight loss may occur initially but isn't recommended long-term without medical supervision.
How do I calculate weight difference in stone and pounds?
Convert both your starting and current weight to the same unit (either all stone/pounds or all kilograms), then subtract. For example, if you went from 12 stone to 10 stone 8 lbs, your difference is 1 stone 6 lbs (approximately 9 kg) loss. Use our weight converter for instant calculations.
Should I weigh myself daily to track weight difference?
Weekly weigh-ins are more reliable than daily measurements. Weight fluctuates due to hydration, hormones, and digestion — daily differences don't reflect true fat loss. Weigh yourself at the same time each week for consistent comparisons.
What does my weight difference tell me about my health?
Weight difference, combined with your BMI and waist circumference, gives a fuller picture of health. Even a 5 to 10% reduction in body weight can lower blood pressure, improve blood sugar control, and reduce cardiovascular risk — benefits that appear well before reaching a "target" weight.
How is weight difference different from BMI change?
Weight difference shows absolute change in kilograms or pounds. BMI change reflects how that weight difference affects your body mass index relative to your height. Use our BMI calculator to see how your weight difference impacts your BMI category and health risk level.
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.