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 Lose 15 Kg: A Realistic UK Guide
Losing 15 kg is an achievable weight loss goal for most UK adults, and even a loss of this magnitude can bring significant health improvements. Whether you're looking to improve your health, reduce the risk of weight-related conditions, or feel better day-to-day, understanding realistic timescales, evidence-based methods, and how to track progress is essential. The NHS recommends losing weight at a steady pace of 0.5–1 kg per week for sustainable, long-term results. This guide covers what a 15 kg weight loss means for your health, how long it typically takes, and the methods that work best.
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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.
What Does 15 Kg Weight Loss Mean for Your Health?
A 15 kg weight loss represents approximately 5–10% of body weight for most UK adults, which is the threshold at which significant health improvements begin. Research shows that losing this amount can reduce blood pressure, improve blood sugar control, lower cholesterol levels, and ease joint pain and mobility issues. For adults with a BMI above 30 (obesity), a 15 kg weight loss can move you into a healthier weight category and substantially reduce the risk of type 2 diabetes, cardiovascular disease, and certain cancers.
Using our free BMI calculator, you can check where your current weight falls and see how your BMI would change after a 15 kg loss. This helps visualise the health benefit in concrete terms. The NHS also emphasises that sustainable weight loss improves mental health, energy levels, and quality of life — benefits that go beyond the numbers on the scales.
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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.
How Long Does It Take to Lose 15 Kg?
Following NHS guidance for safe, sustainable weight loss of 0.5–1 kg per week, losing 15 kg typically takes between 15 and 30 weeks (approximately 3.5 to 7 months). The timescale depends on your starting weight, metabolism, activity level, and how consistently you maintain a calorie deficit. A larger calorie deficit (approximately 750 kcal/day) results in faster loss but requires careful management. For weight management in the UK, prescription weight loss medication may be considered if lifestyle changes alone are insufficient — your GP can assess eligibility based on your BMI and any weight-related health conditions.
Our free progress tracker helps you log weekly weigh-ins and visualise your progress towards your 15 kg goal, keeping motivation high over the months ahead.
Methods that support a 15 kg loss sustainably include: reduced-calorie diet with whole foods, increased physical activity (150+ minutes moderate activity per week), behaviour change strategies, and adequate sleep and stress management. Some people benefit from structured programmes like the NHS Weight Loss Plan, or from working with a dietitian. For adults with a BMI of 30+ or 27+ with weight-related health conditions, GLP-1 weight loss injections (such as Wegovy or Mounjaro) may be prescribed alongside lifestyle changes. Our GLP-1 weight loss calculator can help estimate potential outcomes if medication is being considered. Always consult your GP before starting any weight loss programme or medication.
- 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 15 kg a realistic weight loss goal?
Yes. For most UK adults, 15 kg is realistic and achievable over 3–7 months when combined with a calorie deficit, physical activity, and behaviour change. This amount of loss typically produces noticeable health improvements and fits NHS guidance for sustainable weight management.
How much calorie deficit do I need to lose 15 kg?
A deficit of approximately 500 kcal per day results in 0.5 kg loss per week (15 kg in 30 weeks). A 750 kcal deficit produces 1 kg per week (15 kg in 15 weeks), though this requires careful management and is best done with professional support.
Will I lose 15 kg faster with weight loss medication?
Clinical trials show GLP-1 medications (like Wegovy) and dual GIP/GLP-1 medications (like Mounjaro) may accelerate weight loss when combined with lifestyle changes. Individual results vary significantly. Eligibility requires clinical assessment by your GP or a prescriber.
What's the difference between 15 kg loss and BMI improvement?
The BMI change depends on your height. Use our free BMI calculator to see your current BMI and estimate your BMI after a 15 kg loss. For most adults, 15 kg loss moves you closer to or into the healthy BMI range (18.5–24.9).
Can I support gradual weight management?
Losing 15 kg in 8 weeks requires a very large calorie deficit and gradual weight management, which is not recommended without medical supervision. The NHS recommends 0.5–1 kg per week. Faster loss increases risk of muscle loss, nutritional deficiency, and regaining the weight. Speak to your GP if gradual weight management is being considered.
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.