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 Does Mounjaro Take To Work?
Mounjaro (tirzepatide) doesn't produce immediate results — weight loss takes time. Most people begin noticing effects within the first 2–4 weeks, though significant weight loss typically develops over 8–12 weeks as your dose increases. Because Mounjaro uses a gradual dose titration schedule (starting at 2.5 mg and increasing weekly), your body adjusts gradually, which is safer but means patience is essential. Understanding the timeline helps manage expectations and explains why accessing Mounjaro through NHS or private routes involves planning ahead.
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.
Timeline: When Mounjaro Effects Become Noticeable
Weeks 1–4 (2.5 mg starting dose): Initial appetite suppression may begin, though some people feel minimal change. Nausea is common during this phase and often improves with time. You may notice slightly reduced food cravings or feeling fuller faster.
Weeks 5–12 (5 mg dose): More noticeable appetite reduction and early weight loss typically emerge. Clinical trial data shows measurable weight loss usually becomes apparent by week 8–12. The KwikPen delivery system makes weekly injections straightforward.
Weeks 13+ (escalating to 10 mg, 15 mg): As your dose increases, effects typically become more pronounced. By week 16–20, most people experience significant appetite suppression. Maximum effect usually requires reaching your target dose and maintaining it for several weeks. Individual responses vary — some see faster results, others need longer. Mounjaro vs Wegovy comparisons show similar timelines, though Mounjaro's dual GIP/GLP-1 mechanism may produce results slightly faster for some patients.
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.
Accessing Mounjaro In The UK: Cost And Routes
NHS access: Available through specialist tier 3/4 weight management services following GP referral. NICE has approved tirzepatide for NHS use, but availability and waiting times vary significantly by region and clinical commissioning group (ICB). NHS access is free at point of use but may involve substantial waiting lists.
Private prescription access: Available through GPhC-registered online prescribing services following a clinical assessment. Private Mounjaro costs typically range from £150–£280 per month depending on your dose and provider. A private online consultation usually costs £50–£99 and includes prescriber assessment. Doses escalate weekly, so your monthly costs increase as you progress from 2.5 mg to higher doses. Private access is faster than NHS routes — usually within days rather than months.
- 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 will I lose weight on Mounjaro?
Weight loss varies significantly between individuals. Clinical trials showed average loss of 15–21% of body weight over 72 weeks on the maximum dose. Most people notice initial changes within 2–4 weeks, with more substantial loss by weeks 8–12. Results depend on dose, diet, activity level, and individual metabolism. Your GP or prescriber can discuss realistic expectations for your situation.
Why does Mounjaro use a slow dose increase schedule?
Gradual dose titration (starting 2.5 mg, increasing weekly) allows your body to adjust and reduces side effects like nausea. Jumping to high doses immediately would be less safe and cause worse gastrointestinal symptoms. The slower approach, while requiring patience, produces better long-term outcomes and compliance.
Can I get Mounjaro through the NHS quickly?
NHS access depends on your regional ICB and specialist service availability. Some areas have short waiting lists (weeks), others have waiting lists of many months or over a year. Your GP can refer you to your local tier 3 weight management service to check current waiting times. Private prescription routes are typically faster — usually within days.
What's the difference between Mounjaro and Wegovy timelines?
Both are once-weekly injections with similar overall timelines for noticeable effects (2–4 weeks, significant loss by 8–12 weeks). Mounjaro uses a dual GIP/GLP-1 mechanism and may produce results slightly faster for some people, though individual variation is substantial. Your prescriber can discuss which suits your circumstances better.
Is the cost of private Mounjaro worth it compared to waiting for NHS?
That depends on your personal circumstances, finances, and urgency. NHS access is free but may involve waiting months. Private costs £150–£280/month but provides faster access. Some people choose private initially then switch to NHS when available. Your GP can discuss both options and help you decide what's realistic for your situation.
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.