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
Can I Start Mounjaro on 5mg?
No — Mounjaro always starts at 2.5mg, not 5mg. This lower starting dose allows your body to adjust to the medication and helps minimise early side effects like nausea. After 4 weeks on the initial dose, your prescriber may escalate you to 5mg if tolerated well. Mounjaro (tirzepatide) is a prescription-only injection licensed for weight management in UK adults, and your dosing schedule will be personalised based on your clinical assessment and how you respond to treatment.
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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.
Why Mounjaro Always Starts at 2.5mg
Mounjaro's standard dosing protocol is designed to help your body adapt gradually to the medication. Starting at 2.5mg—the lowest available dose—reduces the risk of severe gastrointestinal side effects, which are most common when first taking GLP-1 and GIP receptor agonists like tirzepatide. After 4 weeks, your prescriber will assess your tolerability and response, then may increase to 5mg. Subsequent escalations follow at 4-week intervals: 7.5mg (weeks 9–12), 10mg (weeks 13–16), 12.5mg (weeks 17–20), and finally 15mg (maximum dose). This titration schedule helps your prescriber find the lowest effective dose for you, rather than starting high and potentially facing excessive side effects. The KwikPen device delivers exactly 2.5mg per injection, so you cannot adjust the dose yourself—any changes must be made by your prescriber following a clinical review.
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.
When Your Prescriber Might Skip Doses
While the standard protocol is 2.5mg → 5mg → 7.5mg and so on, some prescribers may occasionally recommend staying on a particular dose longer if you're tolerating it well and achieving good results. Conversely, if you experience significant side effects, your prescriber may delay escalation or keep you on 2.5mg longer. This is entirely individual and depends on your health, weight loss progress, and how well you tolerate gastrointestinal effects. Never skip prescribed dose escalations without discussing it with your prescriber first—they need to know how you're responding to track your progress safely. Our GLP-1 weight loss calculator can help you understand potential outcomes at different doses, though your actual results will depend on your individual response and adherence to diet and activity 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.
Can a prescriber prescribe Mounjaro starting at 5mg instead of 2.5mg?
No. The UK licence and clinical guidance stipulate a 2.5mg starting dose. Prescribers must follow this protocol. Starting higher would increase the risk of severe nausea and vomiting. Your prescriber will escalate you to 5mg after 4 weeks if you tolerate the initial dose well.
What if I don't tolerate the 2.5mg dose?
If you experience severe side effects on 2.5mg, contact your prescriber immediately. They may delay escalation, reduce frequency temporarily, or discuss whether Mounjaro is right for you. Most people tolerate the starting dose adequately after a few days, though nausea is common initially.
How quickly can I move from 2.5mg to 5mg?
The minimum time between dose increases is 4 weeks. You cannot skip this—it's a safety protocol. Your prescriber needs 4 weeks to assess how you're responding before escalating. Do not request or expect faster escalation.
Is 5mg a common maintenance dose for weight loss?
Yes, many people find 5mg effective for weight management and remain on this dose long-term rather than escalating further. Some achieve their weight loss goals at 5mg or 7.5mg. Your prescriber will help determine the right dose for you based on results and tolerability.
Will starting at 2.5mg mean slower weight loss?
Starting at 2.5mg does not significantly delay weight loss—most loss happens over weeks 5–16 as doses escalate. Clinical trials showed meaningful results with standard titration. Individual results vary, but dose escalation follows the evidence-based protocol designed for safety and efficacy.
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.