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 Take Mounjaro Every 2 Weeks?
No — Mounjaro must be taken as a once-weekly injection. The tirzepatide in Mounjaro is designed to be administered every 7 days, and changing this schedule without medical guidance can affect how well it works and how your body responds. If you're considering a different dosing schedule, speak to your prescriber before making any changes. This guide explains the correct dosing, what to expect during dose titration, and how to manage your Mounjaro prescription in the UK.
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.
Why Mounjaro Must Be Given Once Weekly
Mounjaro's effectiveness depends on maintaining consistent levels of tirzepatide in your bloodstream. The medication is designed as a once-weekly injection through a pre-filled KwikPen device, and clinical trials that established its safety and weight loss benefits were based on this weekly schedule.
Key dosing facts:
- Starting dose: 2.5 mg once weekly for weeks 1–4
- Doses increase at 4-week intervals (5 mg, 7.5 mg, 10 mg, 12.5 mg, 15 mg maximum)
- Minimum gap between doses: 72 hours (3 days) — you can inject up to 2 days early or 2 days late if needed
- Each KwikPen contains 4 doses (one month's supply)
Spacing injections further apart — such as every 2 weeks — would mean you receive only half the intended dose over the same time period, reducing its effects on appetite regulation and weight management. Your prescriber will not recommend bi-weekly dosing, as it falls outside the licensed dosing schedule.
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.
What If You Miss or Need to Delay Your Injection?
Life happens — if you miss your weekly Mounjaro injection, the guidance is straightforward. If it's within 4 days of your missed dose: take it as soon as you remember, then resume your normal weekly schedule. If it's more than 4 days since you should have injected: skip that dose and take your next injection on your normal scheduled day.
Never take a double dose to catch up. If you need to delay your injection by a day or two for practical reasons, that's acceptable — the minimum safe gap is 72 hours — but contact your prescriber's clinic if you need to reschedule regularly. They can discuss whether adjusting your injection day to fit your routine might help.
- 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 happens if I accidentally inject Mounjaro every 2 weeks instead of weekly?
You would receive half the intended dose over the same time period, significantly reducing its effects on appetite and weight management. Contact your prescriber immediately. They may advise adjusting your next injection schedule to get back on track. Never continue bi-weekly dosing without medical guidance.
Can my prescriber change my Mounjaro to a different injection schedule?
Not outside the once-weekly licence. Mounjaro is approved in the UK for once-weekly use only. If once-weekly dosing is difficult for you, discuss this with your prescriber — they may suggest practical solutions like adjusting your injection day or exploring alternative medications.
What's the difference between tirzepatide (Mounjaro) and semaglutide (Wegovy) dosing?
Both are once-weekly injections. Mounjaro is a dual GIP/GLP-1 agonist with a maximum dose of 15 mg weekly, while Wegovy (semaglutide) is a GLP-1 agonist with a maximum dose of 2.4 mg weekly. Both follow weekly schedules; neither is dosed every 2 weeks.
How do I know what dose I should be on?
Your prescriber will start you on 2.5 mg Mounjaro and increase the dose every 4 weeks based on your tolerance and response. Use our free GLP-1 weight loss calculator to understand potential outcomes at different doses, though your actual dose will depend on your clinical assessment.
What if I want to space my injections further apart to save money?
Do not attempt this without medical advice. Mounjaro's cost is managed through private prescription pathways in the UK, but skipping or delaying doses is not a safe cost-saving strategy. Speak to your prescriber about payment plans or discuss your concerns about access and cost openly.
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.