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
When Will You Start To Notice Weight Loss?
Weight loss timelines vary significantly depending on your starting weight, the method you're using, and individual factors like metabolism and adherence to dietary changes. If you're considering weight management through lifestyle changes alone, prescription weight loss medication, or GLP-1 injections like Wegovy, understanding realistic timelines can help you set sustainable goals. This guide explains when you're likely to see visible results and how to track progress effectively with NHS-aligned guidance.
10,000+ calculations today · NHS-aligned thresholds · 100% free
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.
Timeline for Noticing Weight Loss Results
Most people begin to notice physical changes after losing approximately 5–10% of their body weight, though this varies considerably. If you weigh 100kg, this means noticing changes somewhere between 5–10kg lost.
For lifestyle changes alone: At a sustainable rate of 0.5–1kg per week (NHS recommendation), visible changes typically appear within 4–8 weeks. Early signs include looser clothing, reduced bloating, and increased energy.
For GLP-1 weight loss medication (like Wegovy): Clinical trials (STEP data) showed participants experienced noticeable appetite reduction within 2–4 weeks. Weight loss acceleration typically occurs weeks 5–12 as doses increase. Average weight loss in trials was approximately 15% body weight over 68 weeks.
Individual factors affecting timeline: Your starting BMI, age, current medications, metabolic rate, and consistency with dietary changes all influence how quickly you'll notice results. Use our GLP-1 weight loss calculator to estimate potential outcomes based on your individual situation.
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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.
What to Track Beyond the Scale
Weight loss isn't linear—many people experience plateaus or water weight fluctuations that mask fat loss. Track multiple markers of progress: how clothes fit, energy levels, sleep quality, mood, and waist circumference (more relevant to health than total weight alone).
Our free progress tracker helps you log weekly changes and identify patterns over time, making it easier to spot progress even when the scale isn't moving. A loss of just 5% body weight delivers measurable health benefits including improved blood pressure, better blood sugar control, and reduced joint strain—often noticeable before significant scale changes.
For prescription weight loss medication in the UK, your GP or prescriber will review your progress at regular intervals. If using GLP-1 weight loss medication, expect dose adjustments every 4 weeks, with meaningful results typically visible by week 12–16 of treatment.
- 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 quickly will I lose weight on Wegovy or other GLP-1 injections?
Clinical trials showed participants lost an average of 15% body weight over 68 weeks with Wegovy. Individual results vary significantly. Most people notice appetite reduction within 2–4 weeks, with more visible weight loss appearing between weeks 5–12 as doses increase. Your GP or prescriber will monitor your progress and adjust your dose accordingly.
Can I notice weight loss before the scales show it?
Yes. Many people notice clothes fitting differently, increased energy, better sleep, or reduced bloating before significant scale changes. A loss of 5% body weight—often unnoticeable on scales—delivers real health benefits. Our progress tracker helps you log these non-scale victories alongside weight measurements for a complete picture.
Why isn't my weight loss showing week-to-week?
Weight naturally fluctuates daily due to water retention, hormones, digestion, and exercise (muscle weighs more than fat). The NHS recommends weighing yourself weekly and tracking the trend over 4 weeks rather than daily changes. This shows your true progress and helps distinguish genuine fat loss from water weight variations.
Is losing 0.5–1kg per week realistic?
Yes, the NHS recommends this as a safe, sustainable rate. It requires a calorie deficit of approximately 500kcal per day through diet, exercise, or both. This rate minimises muscle loss and is more likely to be sustained long-term. Faster loss is possible with medical support but carries higher risks and isn't necessary for health benefits.
When should I see health improvements, not just weight loss?
Evidence shows that losing just 5–10% of your body weight improves blood pressure, blood sugar control, cholesterol levels, and joint health. These improvements often appear within 8–12 weeks even if total weight loss seems modest. Your GP can monitor these markers. Weight loss is one tool for improving health—focus on consistency rather than speed.
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.