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 Does 1 Kilogram of Fat Actually Mean?
One kilogram of fat is equivalent to approximately 7,700 kilocalories (kcal) of stored energy in your body. Understanding what this means helps you set realistic weight loss goals and recognise the effort required to lose weight sustainably. According to NHS guidance, healthy weight loss is typically 0.5 to 1 kilogram per week, which means losing 1kg of fat requires either a calorie deficit of around 7,700 kcal over several days or weeks. This context helps you appreciate both the challenge and the achievability of gradual weight loss alongside lifestyle changes.
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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 Much Energy is 1 Kilogram of Fat?
Body fat storage: One kilogram of pure body fat contains approximately 7,700 kcal of stored energy. This is why weight loss requires consistent calorie deficit over time—it's not possible to lose 1kg of fat in a single day, and gradual weight management is not recommended by the NHS without medical supervision.
Realistic weight loss rate: The NHS recommends losing 0.5–1kg per week for sustainable results. To lose 1kg of fat, you need a cumulative calorie deficit of around 7,700 kcal. This typically takes between one week (at a 1,100 kcal/day deficit) to multiple weeks (at a more moderate 500 kcal/day deficit).
Why gradual loss matters: Losing weight too quickly increases muscle loss and is harder to maintain long-term. A moderate deficit of 500 kcal/day (achievable through diet and exercise) leads to sustainable loss of approximately 0.5kg per week, allowing your body to preserve muscle mass whilst losing fat.
Clinically BackedWeight Loss
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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.
Where Body Fat is Stored and Why It Matters
Body fat distribution affects your health differently depending on where it's stored. Visceral fat (around organs) is metabolically more active and carries higher health risks than subcutaneous fat (under skin). The NHS emphasises that waist circumference is as important as weight when assessing health risk—men with a waist over 94cm and women over 80cm face increased cardiovascular risk, regardless of BMI.
Use our free BMI calculator alongside the weight converter to understand your current weight in both metric and imperial measurements and assess your healthy weight range. Track your progress with our free progress tracker to monitor changes in how you feel and fit, not just the scales.
Body fat percentage matters more than weight alone. One kilogram of fat takes up more physical space than one kilogram of muscle, so two people at the same weight can look different based on muscle-to-fat ratio. Our free body composition guide explains why building muscle through resistance exercise preserves muscle during weight loss. For personalised advice on healthy fat loss targets, speak to your GP.
- 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.
How long does it take to lose 1kg of fat?
At the NHS-recommended rate of 0.5–1kg per week, losing 1kg of fat takes one to two weeks. This assumes a calorie deficit of 500–1,100 kcal per day from diet and exercise combined. Faster loss is possible but increases muscle loss risk and is harder to sustain long-term.
Is 1kg of fat the same as 1kg of body weight?
No. One kilogram of body weight includes fat, muscle, bone, organs, and water. When you lose 1kg on the scales, it's a mix of fat, muscle, water, and glycogen. To lose 1kg of pure fat, you need a larger calorie deficit than the weight loss shown because muscle loss also occurs.
What's a healthy amount of body fat to lose per week?
The NHS recommends losing 0.5–1kg per week for sustainable, healthy weight loss. This represents mostly fat loss with minimal muscle loss. Faster loss should only occur under medical supervision, such as with very low calorie diets or weight loss medications.
How does 1kg of fat compare to 1kg of muscle?
One kilogram of fat takes up about three times more space than 1kg of muscle, which is why people who build muscle may not see dramatic scale changes but notice improved strength and appearance. Muscle is denser and metabolically more active than fat.
Can weight loss injections help me lose 1kg of fat?
Weight loss medications like Wegovy (semaglutide) are prescription-only and work alongside reduced-calorie diet and exercise. Clinical trials showed average weight loss of around 15% body weight, though individual results vary. Speak to your GP about whether prescription weight loss treatment is suitable for you.
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.