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
Weight Loss Date Estimator — How Long Will It Take?
Estimating your weight loss timeline depends on several factors, including your starting weight, target weight, the approach you choose, and whether you use prescription medication. In the UK, adults eligible for weight management support have options including prescription GLP-1 injections like Mounjaro and Wegovy, NHS-supported programmes, or lifestyle changes alone. Our GLP-1 weight loss calculator can help you project realistic timescales based on clinical evidence. Understanding these timelines helps you set achievable milestones and stay motivated throughout your weight loss 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.
UK-Licensed Prescription Weight Loss Options
Three main prescription weight loss medications are licensed in the UK: Mounjaro (tirzepatide), Wegovy (semaglutide), and Saxenda (liraglutide). Mounjaro users in clinical trials lost an average of 15–21% of their body weight over 72 weeks alongside diet and exercise. Wegovy showed average weight loss of approximately 15% over 68 weeks. Both are once-weekly injections; Saxenda requires daily injections. Eligibility includes adults with a BMI of 30 or above, or 27–29.9 with weight-related health conditions such as type 2 diabetes, high blood pressure, or cardiovascular disease. South Asian, Chinese, Black African, and Black Caribbean adults may have access at lower BMI thresholds due to higher health risks at lower weights. Weight loss with GLP-1 medication typically becomes noticeable within 4–8 weeks, with most significant results between weeks 12–24 as doses increase. Individual timescales vary considerably.
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.
NHS vs Private Access and Your Timeline
In the NHS, prescription weight loss treatment is available through tier 3 specialist weight management services, typically following referral from your GP. Waiting times vary significantly by region—some areas have waits exceeding 12 months. Privately, you can access prescription weight loss medication faster through GPhC-registered online prescribing services, with assessment and prescription within days. Whichever route you choose, medication works best when combined with reduced-calorie eating and increased physical activity. Use our free BMI calculator to check your starting point, and our weight loss calculator to project realistic results based on UK clinical evidence. Your GP can advise whether prescription support is appropriate for your circumstances and health history.
- 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 can I lose weight with prescription weight loss medication in the UK?
Noticeable weight loss typically begins within 4–8 weeks as doses increase. Clinical trials show most significant loss between weeks 12–24. Average loss with Mounjaro is 15–21% of body weight over 72 weeks; Wegovy shows approximately 15% over 68 weeks. However, individual results vary based on adherence, diet, exercise, and starting weight. Your GP or prescriber can give personalised projections.
What's the difference between NHS and private weight loss medication access in terms of timeline?
NHS access through specialist services offers free medication but involves GP referral and often lengthy waiting lists (sometimes 6–12+ months depending on your region). Private online prescribing is faster—assessment and prescription within days—but involves cost (typically £130–£320 monthly). Both approaches use the same UK-licensed medications and follow identical clinical protocols.
How do I estimate my personal weight loss date?
Start by calculating your current BMI using our free BMI calculator to establish your baseline. Then use our GLP-1 weight loss calculator, which projects realistic timescales based on your starting weight, target weight, and medication type. Remember this is an estimate—actual loss depends on diet adherence, exercise, individual metabolism, and medication tolerance. Discuss realistic targets with your GP.
What's the safe rate of weight loss I should aim for?
The NHS recommends losing 0.5–1 kg (1–2 lbs) per week for sustainable, healthy results. This typically requires a calorie deficit of around 500 kcal daily through diet and exercise combined. With prescription GLP-1 medication alongside dietary changes, you may lose more initially. However, very rapid loss can lead to muscle loss and nutrient deficiencies, so medical guidance is important.
Do I need to change my diet and exercise if I'm taking prescription weight loss medication?
Yes. Prescription weight loss medications work best alongside a reduced-calorie diet and increased physical activity. Clinical trials for Mounjaro and Wegovy involved participants following structured eating plans and exercise programmes—medication alone is not sufficient. Your GP, prescriber, or a registered dietitian can advise on sustainable dietary and lifestyle changes to maximise results and maintain weight loss long-term.
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.