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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Weight Loss Timeline Calculator — Plan Your Journey
A weight loss timeline calculator helps you understand how long it realistically takes to reach your goal weight in the UK. Whether you're managing weight through diet and exercise, considering prescription weight loss medication, or tracking progress with GLP-1 injections like Mounjaro or Wegovy, knowing realistic timelines keeps you motivated and accountable. This guide explains how weight loss works, what factors affect your timeline, and how to use the free GLP-1 weight loss calculator on this page to estimate your journey.
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.
How Weight Loss Timelines Work in the UK
Safe weight loss in the UK follows NHS guidance of 0.5–1 kg (1–2 lbs) per week. This rate balances effective results with preserving muscle mass and reducing nutritional deficiencies. The timeline for reaching your goal depends on how much weight you need to lose and which method you choose.
- Diet and exercise alone: Typically requires a 500 kcal daily deficit for approximately 0.5 kg weekly loss
- GLP-1 weight loss injections: Prescription weight loss medication like Wegovy (semaglutide) and Mounjaro (tirzepatide) may accelerate weight loss alongside reduced-calorie diet and increased physical activity. Clinical trials showed participants on GLP-1 medication lost an average of 15–21% of body weight over 68–72 weeks, though individual results vary significantly
- Combination approach: Many people combine lifestyle changes with prescription weight loss medication for faster, more sustainable results
Your personal timeline also depends on your starting weight, current BMI, metabolism, age, and overall health. Use our GLP-1 weight loss calculator above to estimate potential weight loss if you're considering prescription medication.
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 Weight Loss Timeline
Several factors influence how quickly you'll lose weight and reach your goal:
- Starting weight: Larger initial weight losses often occur in the first few weeks (partly water weight), then plateau as body adapts
- Age and metabolism: Metabolic rate slows with age, potentially extending timelines
- Consistency: Adherence to dietary changes and physical activity directly impacts results
- Medical conditions: Thyroid disorders, PCOS, and diabetes affect weight loss rates
- Sleep and stress: Poor sleep and high stress increase cortisol, which can slow weight loss
- Medication choices: If using prescription weight loss medication, the dose prescribed affects timeline. NHS weight management services and private prescribers assess the right medication and dose for you individually
Track your progress weekly using our free progress tracker, but expect natural fluctuations of 1–2 lbs due to water retention and hormonal changes.
- 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 long does it take to lose 1 stone using a weight loss calculator?
Losing 1 stone (6.35 kg) at the NHS-recommended safe rate of 0.5–1 kg per week takes approximately 6–13 weeks with diet and exercise alone. With prescription GLP-1 medication like Wegovy or Mounjaro alongside lifestyle changes, timelines may be shorter, though individual results vary. Use our GLP-1 calculator to estimate your personal timeline.
What's a realistic weight loss timeline for prescription weight loss injections in the UK?
Clinical trials showed participants on Wegovy (semaglutide) lost an average of 15% body weight over 68 weeks, and Mounjaro users lost 15–21% over 72 weeks. These are averages—individual results vary significantly. Timelines depend on starting weight, dose prescribed, diet adherence, and physical activity. Your prescriber will discuss realistic expectations during clinical assessment.
Can I calculate my weight loss timeline using my BMI?
Yes. Your BMI determines your starting health category (underweight, healthy, overweight, or obese). Use our free BMI calculator to find your current BMI, then identify your healthy weight range. Calculate the difference and apply the safe loss rate (0.5–1 kg weekly) to estimate your personal timeline.
Is losing weight faster than 1 kg per week safe in the UK?
The NHS recommends losing no more than 0.5–1 kg per week for sustainable results and muscle preservation. Faster loss (1.5+ kg weekly) is possible with medical supervision or prescription weight loss medication but increases risk of muscle loss and nutritional deficiencies. Always discuss safe loss rates with your GP or prescriber before starting any weight loss programme.
How does a weight loss timeline change with GLP-1 medication like Mounjaro or Wegovy?
GLP-1 medications like Mounjaro and Wegovy may accelerate weight loss when combined with reduced-calorie diet and increased physical activity. Clinical data showed average weight loss of 15–21% over 68–72 weeks. However, these are prescription-only medicines requiring clinical assessment and an individual may not be eligible. Try our GLP-1 weight loss calculator to estimate projected results at different doses.
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.