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 Between Mounjaro Doses?
Mounjaro (tirzepatide) is injected once every week, with a minimum of 72 hours (3 days) between doses. Each KwikPen contains a 4-week supply, and you follow a structured dose escalation schedule over several weeks. In the UK, Mounjaro is a prescription-only medicine that requires clinical assessment before starting. Your prescriber will guide you through the exact timing and dose increases based on your individual response.
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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.
Weekly Dosing Schedule and Dose Escalation
Mounjaro is administered as a once-weekly injection, which means you inject on the same day each week. The minimum safe interval between doses is 72 hours (3 days) — you should not inject sooner than this. Each pre-filled KwikPen delivers a single weekly dose and contains enough medication for 4 weeks of treatment.
Your dose will typically increase every 4 weeks as follows: 2.5 mg for weeks 1–4 (starting dose), 5 mg for weeks 5–8, 7.5 mg for weeks 9–12, 10 mg for weeks 13–16, 12.5 mg for weeks 17–20, and 15 mg from week 21 onwards (maximum dose). Your prescriber may adjust this schedule based on how you respond and any side effects you experience. Some patients stay on lower doses if they achieve good results or experience tolerability issues at higher doses.
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.
Missed Doses and Practical Timing Tips
If you miss a dose, the timing for your next injection depends on how late you are. If it's within 4 days of your missed dose, inject as soon as you remember, then continue with your normal weekly schedule. If it's more than 4 days since your missed dose, skip that dose entirely and take your next injection on your normal scheduled day. Never inject twice in quick succession to make up for a missed dose.
To make injection timing easier, choose the same day each week — for example, every Monday morning. You can adjust your injection day by up to 2 days early or late if needed for convenience, but try to keep to a consistent weekly rhythm. Set a phone reminder or mark it in your calendar to help you stay on track. Use our GLP-1 weight loss calculator to track projected progress as you move through your dose escalation.
- 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's the minimum time between Mounjaro injections?
The minimum safe interval between Mounjaro doses is 72 hours (3 days). You must not inject sooner than this. Mounjaro is designed as a once-weekly injection, so aim for the same day each week if possible, but you can adjust by up to 2 days early or late for convenience.
How many weeks do I stay on each Mounjaro dose?
You typically stay on each dose for 4 weeks before escalating to the next one. Your prescriber may recommend staying longer on a particular dose if you're experiencing good weight loss results or managing side effects well. Some people don't escalate beyond 5 mg or 10 mg if they achieve their goals.
What if I miss a Mounjaro injection?
If you're within 4 days of your missed dose, inject as soon as you remember and continue your normal schedule. If more than 4 days have passed, skip that dose and inject on your normal day. Never double-dose or inject twice within a short period to catch up.
Can I change the day I inject Mounjaro?
Yes, you can adjust your injection day by up to 2 days early or late for convenience. However, try to keep to a consistent weekly rhythm — for example, always inject on a Monday. Setting a phone reminder helps many people stay on track with their weekly schedule.
How long does each Mounjaro KwikPen last?
Each pre-filled KwikPen contains 4 weekly doses, so one pen lasts approximately 4 weeks. You'll need a new pen each month while you're being a UK pharmacy. Your prescriber or pharmacy will arrange repeat supplies as 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.