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 Often Can You Inject Mounjaro?
Mounjaro (tirzepatide) is a once-weekly prescription injection for weight management in UK adults. You inject it the same day each week, and each KwikPen contains four weekly doses. Your prescriber will guide you on your personal injection schedule, which typically starts at 2.5 mg and increases gradually every 4 weeks up to a maximum of 15 mg. If you're considering Mounjaro, our free GLP-1 weight loss calculator can help you estimate potential outcomes at different doses based on clinical trial data.
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.
Once-Weekly Injection Schedule
Mounjaro is always injected once per week — this is the standard injection frequency for tirzepatide in the UK. You choose a day that suits you (for example, every Monday) and inject on the same day each week. Each pre-filled KwikPen device contains exactly four doses, giving you one month of treatment.
- Starting dose: 2.5 mg — weeks 1–4
- First escalation: 5 mg — weeks 5–8
- Second escalation: 7.5 mg — weeks 9–12
- Third escalation: 10 mg — weeks 13–16
- Fourth escalation: 12.5 mg — weeks 17–20
- Maximum dose: 15 mg — week 21 onwards
Your prescriber decides if and when to increase your dose based on how you respond and any side effects. The minimum time between injections is 72 hours (3 days), but the standard is exactly 7 days apart.
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 Dose and Storage Information
If you miss your weekly Mounjaro injection, you can still inject within 4 days of your scheduled dose time. Simply inject as soon as you remember, then continue your normal weekly schedule from that point.
However, if more than 4 days have passed, skip that dose and take your next injection on your normal scheduled day — never take a double dose.
Store unopened Mounjaro pens in a refrigerator at 2–8°C. After first use, you can keep the pen at room temperature (below 30°C) for up to 30 days. Unlike some other weight loss injections, the once-weekly schedule of Mounjaro makes it straightforward to track — the same day each week forms an easy routine.
- 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 you inject Mounjaro more than once a week?
No. Mounjaro is only prescribed as a once-weekly injection. Injecting more frequently than once weekly is not medically appropriate and increases the risk of side effects. Your prescriber will set your dose based on clinical guidelines, not injection frequency.
What if I inject Mounjaro 2 days early by accident?
If you accidentally inject 2 days early, you'll still be within a safe interval. However, try to maintain a consistent weekly schedule going forward — the same day each week is easiest to remember. If you're concerned, contact your prescriber or pharmacist.
Is Mounjaro the same injection frequency as Wegovy?
Yes. Both Mounjaro (tirzepatide) and Wegovy (semaglutide) are once-weekly injections in the UK. The main difference is their mechanism: Mounjaro is a dual GIP and GLP-1 receptor agonist, while Wegovy is a GLP-1 agonist only. Clinical trial results show different average weight loss percentages, but individual results vary.
Can I inject Mounjaro myself or does a GP have to do it?
You can inject Mounjaro yourself using the pre-filled KwikPen device — it's designed for self-injection into the stomach, thigh, or upper arm. Your prescriber or pharmacist will show you the correct technique. If you prefer, you can ask a healthcare professional to administer it, but self-injection is standard.
What happens if I'm 5 days late for my Mounjaro injection?
If you're more than 4 days late, skip that dose and inject on your normal scheduled day. Do not take a double dose to catch up. This guidance helps prevent side effects from dose overlap. If you frequently miss doses, speak to your prescriber about strategies to help you remember.
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.