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 Before Mounjaro Kicks In — What to Expect
Most people notice the first appetite-suppressing effects of Mounjaro within 2–4 weeks of starting treatment, though this varies. However, meaningful weight loss typically becomes visible after 8–12 weeks as your body adjusts to the medication and you build sustainable habits. Understanding the timeline, cost, and access routes in the UK helps you make an informed decision. Both NHS and private routes are available, with different timescales and expenses.
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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 Costs and Access Routes for Mounjaro
Mounjaro (tirzepatide) is available in the UK through NHS specialist weight management services and private online prescribing. On the NHS route, you'll be referred to a tier 3 specialist service by your GP — though waiting lists vary significantly by region and can take months or even years. When prescribed through NHS services, Mounjaro is provided at no additional cost beyond standard NHS prescription charges (currently £9.90 per item in England, or free if eligible).
Private prescription costs typically range from £129–£280 per month depending on your dose. A Mounjaro KwikPen contains four weekly injections, so each pen lasts one month. Most private prescribers require an initial online consultation (£30–£100) followed by ongoing follow-up appointments. Payment is per dose, so costs increase as you titrate from the starting 2.5 mg dose upwards towards the maximum 15 mg. Using our GLP-1 weight loss calculator can help you estimate costs at different dose levels.
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: Timeline and Process
The NHS route offers lower cost but longer waits—some regions have waiting lists of 12+ months for specialist assessment. Once accepted, you'll be monitored regularly by NHS staff at no extra cost. The private route is faster: you can have a prescription within 24–48 hours of an online consultation with a UK-licensed prescriber, then collect from a GPhC-registered pharmacy. You'll manage your own dose titration (increasing from 2.5 mg to 5 mg, then escalating every 4 weeks) with support from your prescriber. Private prescribing is typically used by people who don't want to wait for NHS services or who don't meet local NHS criteria. Both routes require a clinical assessment confirming you're eligible—BMI ≥30, or ≥27 with weight-related health conditions like type 2 diabetes, hypertension, or sleep apnoea.
The NHS route offers lower cost but longer waits—some regions have waiting lists of 12+ months for specialist assessment. Once accepted, you'll be monitored regularly by NHS staff at no extra cost. The private route is faster: you can have a prescription within 24–48 hours of an online consultation with a UK-licensed prescriber, then collect from a GPhC-registered pharmacy. You'll manage your own dose titration (increasing from 2.5 mg to 5 mg, then escalating every 4 weeks) with support from your prescriber. Private prescribing is typically used by people who don't want to wait for NHS services or who don't meet local NHS criteria. Both routes require a clinical assessment confirming you're eligible under current NHS NICE guidance.
- 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 does Mounjaro start to work?
Most people feel reduced appetite within 2–4 weeks of the first injection. Noticeable weight loss typically appears after 8–12 weeks as your body adjusts and you build consistent eating habits. Individual responses vary significantly based on diet, activity level, and metabolism.
How much does Mounjaro cost privately in the UK?
Private Mounjaro costs typically range from £129–£280 per month depending on your dose. Starting dose (2.5 mg) is usually cheaper; maximum dose (15 mg) costs more. Add initial consultation fees (£30–£100) and ongoing follow-up appointments to your total monthly cost.
Can I get Mounjaro on the NHS in the UK?
Yes—Mounjaro is available through NHS tier 3 specialist weight management services. You'll need a GP referral and must meet eligibility criteria (BMI ≥30, or ≥27 with weight-related health conditions). Waiting times vary by region; some areas have 12+ month waits. Prescription cost is standard NHS rate (£9.90 in England).
How does Mounjaro compare to Wegovy for timing and cost?
Both Mounjaro and Wegovy start showing effects within 2–4 weeks, though weight loss becomes visible around 8–12 weeks. Mounjaro is a dual GIP/GLP-1 agonist; Wegovy is GLP-1 only. Private costs are similar (£130–£280/month), and both are available through NHS and private routes in the UK.
What happens if Mounjaro isn't working after 3 months?
If you haven't seen appetite suppression or weight changes after 12 weeks (three injections), discuss with your prescriber. You may need a dose increase—Mounjaro requires escalation every 4 weeks until you reach an effective dose. Your prescriber will assess whether the medication is right for you and consider alternatives if needed.
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.