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 a once-weekly injection, meaning you inject yourself exactly 7 days apart. Each dose should be taken on the same day of the week, every week. However, the minimum time between doses is 72 hours (3 days) if you need to adjust your injection day slightly. In the UK, Mounjaro is a prescription-only medicine available through NHS specialist weight management services or private prescribers following clinical assessment. Understanding your dosing schedule is essential for consistent results.
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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.
Mounjaro Dosing Schedule and Timing
Standard dosing interval: Mounjaro is injected once every 7 days, always on the same day of the week. Each Mounjaro KwikPen contains 4 doses (a 4-week supply). Your prescriber will advise which day suits your routine best—many patients choose Monday or Friday for ease of remembering.
Minimum time between doses: If you need to change your injection day, there must be at least 72 hours (3 days) between doses. For example, if you normally inject on Monday, you could inject on Thursday instead, but not sooner. Once you've adjusted the day, continue with your new schedule.
Dose escalation timing: When increasing your dose (from 2.5 mg to 5 mg, for example), you must stay on each dose for at least 4 weeks before escalating. This allows your body to adjust and helps your prescriber monitor side effects.
- Week 1–4: 2.5 mg once weekly
- Week 5–8: 5 mg once weekly (if escalating)
- Week 9–12: 7.5 mg once weekly (if continuing escalation)
Always follow your prescriber's personalised escalation plan—some patients may stay at a lower dose if it's working well.
Clinically BackedWeight Loss
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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 Adjusting Your Schedule
If you miss a Mounjaro injection, the action depends on how late you are. Within 4 days of your scheduled injection: inject as soon as you remember, then continue your normal weekly schedule from that point. More than 4 days late: skip that dose and inject on your next scheduled day—do not double up.
It's important to set a weekly reminder on your phone or calendar to avoid missed doses, as consistent weekly dosing supports steady weight management. If you frequently struggle to remember your injections, discuss this with your prescriber or GP—they may suggest alternative strategies. Our free GLP-1 weight loss calculator can help you track projected progress once you're on a stable dose, and the progress tracker lets you log your weight journey week by week.
- 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 I inject Mounjaro at a different time of day each week?
Yes. Mounjaro can be injected at any time of day—morning, afternoon, or evening. What matters is injecting once every 7 days, ideally on the same day of the week. You don't need to inject at the exact same time, just within a 24-hour window of your chosen day. Pick a convenient time that fits your routine.
What happens if I inject Mounjaro less than 72 hours apart?
Injecting Mounjaro less than 72 hours apart is not recommended and increases the risk of side effects or overdose. Always maintain at least 3 days between doses. If you accidentally inject too soon, contact your prescriber or pharmacist for advice before your next scheduled injection.
Is Mounjaro available on the NHS in the UK?
Yes, Mounjaro (tirzepatide) is approved by NICE and available on the NHS through specialist tier 3 weight management services. However, access varies significantly by region and waiting lists can be long. Many people access Mounjaro privately through a GPhC-registered online pharmacy following a clinical assessment from a UK-licensed prescriber.
Can I switch my Mounjaro injection day?
Yes, you can change your injection day, but you must allow at least 72 hours between your last dose and your new dose. For example, if you inject on Monday, you could move to Thursday (72 hours later) and then continue every 7 days from Thursday. Inform your prescriber of the change to keep your records accurate.
How long does a Mounjaro KwikPen last?
Each Mounjaro KwikPen contains 4 weekly doses, so one pen lasts 4 weeks. You'll need 13 pens per year for continuous treatment. Unopened pens must be stored in the fridge at 2–8°C. After first use, a pen can be kept at room temperature (below 30°C) for up to 30 days, then must be discarded.
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.