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
Week By Week Weight Loss — What to Expect
Week-by-week weight loss varies significantly between individuals, depending on your starting point, lifestyle changes, and whether you're using prescription weight loss medication. The NHS recommends losing weight at a safe, sustainable rate of 0.5 to 1 kg (1 to 2 lbs) per week. Understanding realistic timelines helps you stay motivated and make informed decisions about your weight management approach. This guide explains what to expect, the factors that influence your progress, and how to track your results effectively using evidence-based methods aligned with UK health 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.
Safe Weekly Weight Loss Rates and Realistic Expectations
The NHS recommends a safe weight loss rate of 0.5 to 1 kg per week for sustainable results. This typically requires a calorie deficit of around 500 kcal per day, which can be achieved through a combination of dietary changes and increased physical activity. Losing weight faster than this can lead to muscle loss, nutritional deficiencies, and increased risk of regaining the weight. Individual results vary considerably based on your starting BMI, age, metabolism, and how strictly you follow your plan. Use our free BMI calculator to establish your starting point, then set realistic weekly targets. With prescription weight loss medication like GLP-1 injections, some people may experience faster initial loss, though results vary. The first 1–2 weeks often show larger drops due to water loss rather than fat loss—this is normal. Expect more consistent, steady progress from week three onwards. Tracking your progress weekly using our free progress tracker helps maintain motivation and identify patterns in your journey.
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 Your Week-to-Week Progress
Multiple factors influence weekly weight loss outcomes, even when you're following the same plan. Hormonal fluctuations, water retention, stress levels, sleep quality, and exercise intensity all play a role. Women may notice weight fluctuations linked to their menstrual cycle—this is completely normal. Medications, underlying health conditions, and how quickly your metabolism adapts also matter. Some weeks you'll lose more than others; this variation is expected and doesn't mean your approach has failed. If you're using GLP-1 weight loss injections as part of prescription weight loss medication, your results may differ from others on the same dose. Focus on the trend over 4–6 weeks rather than daily or weekly fluctuations. Our GLP-1 weight loss calculator can help you understand potential timelines if you're considering medication-assisted weight management. Remember that non-scale victories—improved energy, better fitness, clothes fitting differently—are equally important markers of progress.
- 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 should I lose per week?
The NHS recommends losing 0.5 to 1 kg (1 to 2 lbs) per week for sustainable, healthy weight loss. This typically requires a calorie deficit of around 500 kcal per day through diet and exercise combined. Faster loss can lead to muscle loss and is harder to maintain long-term. Your GP can advise on safe targets for your individual circumstances.
What causes larger weight loss in the first week?
Initial weight loss in week one is largely water loss, not fat loss. When you reduce calories and carbohydrates, your body uses stored glycogen, which holds water. This effect typically stabilises after 2–3 weeks. Expect more consistent fat loss from week three onwards, usually 0.5–1 kg per week.
Why do my weekly results vary so much?
Hormonal changes, water retention, stress, sleep, and exercise intensity all affect weekly fluctuations. Women's results often vary with their menstrual cycle. These variations are completely normal. Track your progress over 4–6 weeks rather than weekly to see the true trend and avoid discouragement.
Can prescription weight loss medication speed up weekly weight loss?
GLP-1 medications like Wegovy or Mounjaro may help achieve weight loss alongside diet and exercise, though individual results vary. Clinical trials showed average weight loss of 14–21% of body weight over several months. Your prescriber will discuss realistic timelines and monitor your progress during treatment.
How do I track week-by-week progress accurately?
Weigh yourself at the same time each week (ideally morning, after the toilet, before eating) using the same scales. Our free progress tracker helps you log weekly results and identify patterns. Also measure your waist circumference and note non-scale victories like energy levels and fitness improvements.
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.