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
When Is Best To Take Mounjaro? Weekly Timing & Injection Guide
Mounjaro (tirzepatide) is a once-weekly injection, meaning you take it the same day each week — but the specific time of day is flexible. Unlike some medications, there's no "best time" for Mounjaro in terms of morning versus evening; what matters most is consistency and choosing a day and time that fits your routine. This guide covers UK prescription guidance on timing, injection sites, storage, and how our GLP-1 weight loss calculator can help you track progress alongside your Mounjaro doses.
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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 Injection Timing — What the Evidence Shows
Mounjaro is flexible on timing: You inject once per week on the same day, but whether you choose Monday morning or Thursday evening doesn't significantly affect how the medication works. Clinical guidance from Eli Lilly and UK prescribers emphasises consistency — picking a day and time you'll remember is more important than a specific "optimal" time.
Weekly dosing schedule: Each KwikPen contains four weekly doses. You'll progress through dose increases every 4 weeks minimum: starting at 2.5 mg, then 5 mg, 7.5 mg, 10 mg, 12.5 mg, and up to the maximum 15 mg. Your prescriber determines timing of increases based on your response and tolerability.
- Set a recurring phone reminder for your chosen injection day
- Pick a time that's easiest to remember — morning, lunchtime, or evening all work equally
- Some people inject on the same day they take other weekly medications for easier memory
- If you miss a dose within 4 days, inject as soon as you remember; if more than 4 days have passed, skip to your next scheduled dose
Unlike oral medications, Mounjaro doesn't need to be taken with or without food — you can inject regardless of whether you've eaten.
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.
Storage & Injection Site Rotation — Practical Guidance
Storage before use: Unopened Mounjaro pens must be refrigerated at 2–8°C in their original carton. Once you've used a pen for the first time, it can be kept at room temperature (below 30°C) for up to 30 days — this flexibility makes it easier to carry during daily life.
Injection sites: You can inject Mounjaro into your stomach (abdomen), upper thigh, or upper arm. Rotate your injection site each week to prevent skin irritation and lipodystrophy (thickening of fatty tissue). If you inject into your stomach on week one, try your thigh the next week, then your arm, then rotate back.
Always check that your pen hasn't been frozen — if it has, dispose of it safely and contact your prescriber. Track your weekly injections and weight progress using our free progress tracker to monitor how the tirzepatide dose is working for you over time.
- 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 take Mounjaro at different times each week?
Mounjaro works best on a consistent weekly schedule, but the exact time doesn't matter — morning, afternoon, or evening all work equally. The key is choosing a day and time you'll remember every week. If timing varies by a few hours, it won't reduce effectiveness, but aim for the same day each week.
What if I forget my Mounjaro injection?
If you remember within 4 days of your missed dose, inject as soon as possible and continue your normal schedule the following week. If more than 4 days have passed, skip that dose and take your next injection on your regular scheduled day. Never double-dose to make up a missed injection.
Can I take Mounjaro with food or on an empty stomach?
Mounjaro timing is not affected by food or meals — you can inject at any time regardless of what you've eaten. This flexibility is one advantage of injectable medications over oral tablets, which sometimes need to be taken with or without food.
How long does each Mounjaro KwikPen last?
Each KwikPen contains four weekly doses, so one pen lasts approximately 4 weeks. Your prescriber will provide enough pens to cover your treatment. Store unopened pens in the fridge and opened pens at room temperature for up to 30 days.
Is there a best day of the week to take Mounjaro?
No — any day of the week works equally well. Choose whichever day is easiest for you to remember. Many people pick Monday to start their week, but Thursday, Sunday, or any other day is just as effective. Consistency matters more than which specific day you choose.
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.