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
How Long Does It Take To See Weight Loss?
The timeline for seeing weight loss varies significantly depending on your starting point, metabolism, diet, and whether you're using prescription weight management medication. Most people begin noticing changes within 2–4 weeks of making lifestyle changes or starting treatment, though visible results often take 6–8 weeks. The NHS recommends aiming for sustainable weight loss of 0.5–1 kg per week, which means meaningful results typically emerge within the first month. However, individual experiences differ widely — some see faster initial changes, others progress more gradually.
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.
Realistic Timeline for Seeing Weight Loss Results
When you start a weight loss journey — whether through dietary changes, increased physical activity, or prescription medication like GLP-1 weight loss injections — the timeline depends on several factors. In the first 1–2 weeks, you may experience initial water weight loss, particularly if reducing carbohydrate intake. This isn't fat loss, so it can fluctuate. Between weeks 2–4, many people notice their clothes fit differently or feel less bloated, even if the scales haven't shifted dramatically. After 6–8 weeks, measurable weight loss typically becomes visible on the scales.
- Initial water weight loss: days 1–14
- First visible changes: weeks 2–4
- Sustained fat loss visible: weeks 6–8+
- Significant health improvements: 8–12 weeks onwards
Using our GLP-1 weight loss calculator can help you project realistic timelines based on the dose and medication you're using. The NHS recommends a sustainable rate of 0.5–1 kg per week, which translates to approximately 2–4 kg per month.
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.
Factors That Affect How Quickly You Lose Weight
Several variables influence your personal weight loss timeline. Starting weight: People with a higher BMI often see faster initial results because larger calorie deficits are easier to achieve. Age and metabolism: Metabolism naturally slows with age, so weight loss may take longer for older adults. Gender: Hormonal differences mean men typically lose weight slightly faster than women initially. Consistency: Regular adherence to dietary changes and physical activity makes the biggest difference.
If taking prescription weight loss medication like Mounjaro or Wegovy, the timeline depends on your dose escalation — most people reach their target dose after 16–20 weeks, with weight loss continuing throughout the adjustment period. Check your BMI and track progress using our free progress tracker to monitor trends over time.
- 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.
Will I see weight loss in the first week?
Possibly, but initial losses in week one are typically water weight rather than fat loss, especially if reducing calories or carbs. This can be 1–2 kg initially but may fluctuate. Real fat loss becomes visible after 2–4 weeks of consistent effort.
How much weight should I expect to lose per week?
The NHS recommends a safe, sustainable rate of 0.5–1 kg per week. This equals approximately 2–4 kg per month. Faster loss is possible with prescription medication or supervised low-calorie diets, but slower, steady loss is more sustainable long-term.
Does weight loss happen faster with GLP-1 medication like Wegovy?
Clinical trials show that GLP-1 injections like Wegovy support greater weight loss alongside lifestyle changes, but timelines vary individually. Initial changes may appear within 2–4 weeks, with more significant results after 8–12 weeks. Our GLP-1 weight loss calculator can help estimate your potential timeline.
Why haven't I lost weight after two weeks?
Early plateaus are common and don't mean it isn't working. Your body needs time to adapt. Ensure you're maintaining a calorie deficit, staying hydrated, sleeping adequately, and being consistent. If using prescription medication, you may still be on a starting dose — results typically improve as your dose increases.
What can I do to speed up weight loss safely?
Focus on consistency rather than speed. Combine a moderate calorie deficit (500 kcal daily for ~0.5 kg weekly loss) with regular physical activity and adequate sleep. If eligible, your GP can discuss prescription weight management options. Use our BMI calculator to track your progress and adjust your approach based on results.
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.