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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What Is The Semaglutide Starting Dose For Weight Loss?
Semaglutide is a GLP-1 receptor agonist prescription-only injection licensed in the UK for weight management. The semaglutide starting dose for weight loss is 0.25mg, administered as a once-weekly injection under the brand name Wegovy. This low starting dose allows your body to adapt to the medication before gradually increasing over several weeks. Individual tolerance and response vary, so a prescriber will assess whether semaglutide is suitable for you based on your personal health profile and weight management goals.
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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 The Semaglutide Dosing Schedule Works
Semaglutide for weight loss follows a structured dose escalation schedule designed to minimise side effects and allow your body to adjust. The standard weekly weight loss injection protocol is:
- Weeks 1–4: 0.25mg once weekly (starting dose)
- Weeks 5–8: 0.5mg once weekly
- Weeks 9–12: 1mg once weekly
- Weeks 13–16: 1.7mg once weekly
- Week 17 onwards: 2.4mg once weekly (maximum maintenance dose)
Each dose is injected under the skin once per week on the same day. You remain on each dose for a minimum of 4 weeks before increasing, giving your body time to adjust. Results from clinical trials (STEP-1) showed that at the maximum 2.4mg dose, participants lost an average of approximately 14.9% of their body weight over 68 weeks — though individual results vary significantly. The gradual increase helps reduce nausea and digestive side effects that are common when starting GLP-1 medications.
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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
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Why Start Low And Increase Gradually?
Starting at 0.25mg—the lowest semaglutide dose—serves an important clinical purpose. A low starting dose allows your body to become accustomed to the medication's effects before moving to higher, more potent doses. The most common side effects of semaglutide (nausea, diarrhoea, constipation, and stomach discomfort) are often dose-related. By beginning at 0.25mg, most people experience milder side effects that typically improve within a few days. This approach supports better tolerance and adherence to treatment. Your prescriber may occasionally recommend staying on a lower dose longer if you experience significant side effects, or may accelerate the schedule if you tolerate the medication well. Use our free GLP-1 weight loss calculator to explore potential outcomes at different doses based on clinical evidence.
- 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.
Is semaglutide 0.25mg the same as Ozempic?
Both Wegovy and Ozempic contain semaglutide, but they are different products. Ozempic (up to 2mg) is licensed for type 2 diabetes management, not weight loss. Wegovy (0.25mg to 2.4mg) is the licensed weight management version in the UK. Using Ozempic for weight loss is off-label. Always ensure your prescription specifically states Wegovy for weight management.
How long do I stay on the starting dose of 0.25mg?
You remain on the 0.25mg starting dose for 4 weeks (weeks 1–4). After this period, if you tolerate it well, your prescriber will increase you to 0.5mg. If you experience significant side effects, your prescriber may extend the timeline at 0.25mg before escalating.
What happens if I cannot tolerate the 0.25mg starting dose?
If you experience severe nausea, vomiting, or other significant side effects at 0.25mg, inform your prescriber immediately. They may recommend staying on this dose longer, adjusting your diet, or in some cases, reconsidering whether semaglutide is appropriate for you. Never stop or adjust doses without guidance.
Will I experience side effects at the starting dose?
Nausea is common at any dose but often milder at 0.25mg. Many people experience no significant side effects. Common effects include mild nausea, diarrhoea, constipation, and stomach discomfort. These typically resolve within days to weeks as your body adapts. Staying well-hydrated and eating small, frequent meals can help.
How do I know if semaglutide is right for me?
A UK-licensed prescriber will assess your eligibility through a clinical evaluation. You may be eligible if you have a BMI of 30kg/m² or above, or 27–29.9kg/m² with weight-related health conditions such as type 2 diabetes or high blood pressure. Use our free BMI calculator to check your starting point, then consult your GP or a licensed prescriber for personalised advice.
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.