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
12 Week Weight Loss — What's Realistic and How to Achieve It
A 12 week weight loss timeline is realistic for steady, sustainable progress. Following NHS weight management UK guidance, most adults can expect to lose between 6–12 kg (1–2 stone) over 12 weeks through a combination of dietary changes and increased physical activity. The exact amount depends on your starting weight, age, metabolism, and whether you use prescription weight loss medication or lifestyle changes alone. This guide explains what's achievable, how fast is safe, and the different approaches available to you.
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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.
Safe Weight Loss Rates and 12 Week Targets
The NHS recommends losing weight at a rate of 0.5 to 1 kg per week for sustainable, healthy results. Over 12 weeks, this means a realistic target is 6–12 kg (approximately 1–2 stone).
Faster weight loss is possible but carries higher risks of muscle loss, nutritional deficiencies, and weight regain. A calorie deficit of around 500 kcal per day typically results in approximately 0.5 kg loss per week. To achieve this, you might reduce daily intake by 500 kcal, increase activity to burn 500 kcal, or combine both approaches.
Your starting weight matters too — people with higher BMI often lose weight faster initially due to having more excess weight to shed. Use our free BMI calculator to check your current status and understand your baseline.
- Sustainable: 0.5–1 kg per week = 6–12 kg over 12 weeks
- Aggressive (not recommended without medical support): 1–2 kg per week
- Very rapid: over 2 kg per week (requires medical supervision)
Clinically BackedWeight Loss
No appointments. No waiting rooms. Just care — from a UK-regulated online pharmacy.
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.
Weight Loss Methods Available Over 12 Weeks
In the UK, you have several approaches for 12 week weight loss:
- Lifestyle changes alone: Diet and exercise typically result in 6–8 kg over 12 weeks
- NHS weight loss programme: Access through your GP, includes behaviour change support
- Prescription weight loss medication (GLP-1): Wegovy or Mounjaro alongside lifestyle changes may help achieve higher weight loss through reduced appetite
- Structured diet programmes: Low-calorie diet (1000–1500 kcal/day) under guidance can accelerate results
Clinical trials of GLP-1 weight loss medication show participants lose approximately 15–21% of body weight over longer periods, though individual results vary significantly. If you think prescription weight loss medication might help, your GP can assess your eligibility based on your BMI and health status. Try our free GLP-1 weight loss calculator to see potential outcomes at different doses.
- 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 much weight can I realistically lose in 12 weeks?
At the safe NHS-recommended rate of 0.5–1 kg per week, you can expect to lose 6–12 kg (1–2 stone) in 12 weeks through lifestyle changes. With prescription weight loss medication alongside diet and exercise, some people may lose more, though individual results vary significantly. Use our free BMI calculator to establish your baseline.
Is 12 weeks enough time to see real health benefits from weight loss?
Yes. Research shows that losing even 5–10% of your body weight can meaningfully improve blood pressure, blood sugar control, joint pain, and sleep quality. Over 12 weeks of consistent effort, you'll likely notice improvements in energy, mood, and how clothes fit before the full health benefits appear.
Can I lose weight faster than 1 kg per week?
Faster weight loss is possible but not recommended without medical supervision. Very rapid loss (over 2 kg per week) increases risks of muscle loss, gallstones, and nutritional deficiencies. If you're interested in faster results, ask your GP about prescription weight loss medication or specialist weight management services.
Should I try prescription weight loss medication for a 12 week goal?
If your BMI is 30 or above, or 27 or above with weight-related health conditions, you may be eligible. Prescription medications like Wegovy are prescription-only and require a clinical assessment. They work best alongside reduced-calorie diet and increased physical activity, not as replacements for lifestyle change.
How do I track my 12 week weight loss progress?
Weigh yourself once weekly (same day, same time) and log the results. Our free progress tracker helps you visualise trends over weeks — weight fluctuates day-to-day due to water retention and digestion, so weekly tracking is more meaningful than daily weighting.
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.