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 Much Is One Dose of Mounjaro?
Each Mounjaro KwikPen contains four doses of tirzepatide, providing a four-week supply. The dose you receive depends on your individual treatment plan and how your body responds to the medication. Doses range from 2.5 mg (starting dose) up to 15 mg (maximum), with escalation happening every four weeks. Your prescriber will determine which dose is appropriate for you following a clinical assessment. Understanding your specific dose helps you track your treatment and manage your weight loss journey effectively. Our GLP-1 weight loss calculator can help you explore potential outcomes at different dose levels.
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.
Mounjaro Dose Schedule and KwikPen Contents
Each Mounjaro KwikPen contains exactly four weekly doses. Because Mounjaro is injected once weekly, one pen lasts four weeks. The dose inside each pen varies depending on your treatment stage:
- 2.5 mg — Weeks 1–4 (starting dose for dose adjustment)
- 5 mg — Weeks 5–8+ (first maintenance dose)
- 7.5 mg — Weeks 9–12+ (dose escalation if needed)
- 10 mg — Weeks 13–16+ (further escalation available)
- 12.5 mg — Weeks 17–20+ (dose titration continues)
- 15 mg — Week 21 onwards (maximum dose)
Your prescriber will keep you on each dose for a minimum of four weeks before increasing. This ensures your body adapts safely and you experience the full benefit. In clinical trials, the average weight loss increased with higher doses — participants on 15 mg tirzepatide achieved approximately 20.9% average body weight loss alongside diet and exercise changes.
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 Access and UK Prescription Context
In the UK, Mounjaro is available through both NHS specialist tier 3 weight management services and private prescribing routes. NHS eligibility requires referral to a specialist weight management service and assessment against NICE guidelines. You must have a BMI of 30 kg/m² or above, or 27–29.9 kg/m² with weight-related health conditions such as type 2 diabetes or high blood pressure.
NHS availability varies significantly by region and waiting times can be lengthy. Private prescribing offers faster access following an online clinical assessment with a UK-licensed prescriber. Whichever route you use, your prescriber will start you on 2.5 mg and adjust upwards based on your tolerance and response. Use our BMI calculator above to check whether you might meet eligibility criteria.
- 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.
What exactly comes in one Mounjaro KwikPen?
One KwikPen contains four pre-filled doses of tirzepatide, providing a four-week supply. Each week you inject one dose. The strength of the pen (2.5 mg, 5 mg, 7.5 mg, etc.) depends on your treatment stage. Pens are stored in the fridge and kept in their original carton until use.
Can I adjust my Mounjaro dose myself?
No. Dose adjustments must only be made by your prescriber. You will stay on each dose for a minimum of four weeks. Your prescriber reviews how you're tolerating the dose and whether escalation is needed. Never increase or decrease your dose without clinical guidance.
What's the difference between Mounjaro and Wegovy doses?
Mounjaro (tirzepatide) and Wegovy (semaglutide) use different mechanisms and dose ranges. Mounjaro starts at 2.5 mg and goes up to 15 mg weekly. Wegovy starts at 0.25 mg and reaches 2.4 mg maximum. Approximate equivalences exist but any switch must be managed by your prescriber — there's no official conversion chart.
How long does one Mounjaro pen last?
One KwikPen lasts exactly four weeks because it contains four weekly doses. You'll need a new pen every month if you're receiving regular treatment. Plan refills accordingly with your prescriber or pharmacy to avoid gaps in your treatment schedule.
Does a higher Mounjaro dose mean more weight loss?
Clinical trials showed that higher doses were associated with greater average weight loss — 15 mg achieved approximately 20.9% average loss versus 15% at 5 mg. However, individual results vary significantly. Your prescriber will find the dose that works best for your body and tolerability, not necessarily the maximum dose.
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.