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
Best Time of Day to Take Mounjaro for Weight Loss
The best time to take your weekly Mounjaro injection depends on your personal routine rather than a specific time of day—the medication works the same whether you inject Monday morning or Friday evening. What matters is consistency: choosing a day and time that fits your lifestyle helps you remember your once-weekly dose. Unlike some medications, Mounjaro (tirzepatide) doesn't require taking it with food, on an empty stomach, or at a particular hour. This flexibility makes it easier to fit into your schedule while managing your weight loss journey alongside a reduced-calorie diet and increased physical activity.
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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.
How Mounjaro and Wegovy Dosing Schedules Compare
Both Mounjaro and Wegovy are once-weekly weight loss injections licensed in the UK, but they work on different schedules. Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist that starts at 2.5 mg and increases gradually over weeks—you stay on each dose for a minimum of 4 weeks before escalating, reaching a maximum of 15 mg. Wegovy (semaglutide) is a single-action GLP-1 agonist that starts at 0.25 mg and titrates more gradually, reaching a maximum of 2.4 mg. Clinical trial data shows Mounjaro achieved average weight loss of approximately 20.9% body weight at the highest dose, whilst Wegovy showed around 14.9% in equivalent trials—though individual results vary significantly. The key timing difference is that both are injected once per week on the same day, and your Mounjaro KwikPen or Wegovy pen contains four weekly doses in one prefilled device.
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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.
Timing and Consistency Matter More Than Clock Time
Since Mounjaro works continuously throughout the week after injection, the exact hour you inject is less important than picking a day and sticking to it. Many people choose the same day each week—Monday mornings, for example—to build a routine and avoid missing doses. You'll receive a UK prescription for weight loss from a licensed prescriber following a clinical assessment, and your instructions will specify your injection day. If you miss a dose by more than 4 days, skip that dose and take your next one on your regular schedule—never double-dose. Some people find it helpful to set a phone reminder on their chosen day. Use our free GLP-1 weight loss calculator to explore potential results at different doses, and track your progress with our free progress tracker to see how consistent dosing supports your weight loss 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.
Does it matter what time of day I inject Mounjaro?
No—Mounjaro works the same regardless of whether you inject in the morning, afternoon, or evening. What matters is choosing a consistent day each week and sticking to it. Most people pick a specific day (e.g. Monday) to build a routine and reduce the chance of missing a dose.
Can I take Mounjaro with food or do I need an empty stomach?
Mounjaro does not need to be taken on an empty stomach or with food—you can inject it anytime that suits your routine. The medication works independently of your meal timing, though you'll still benefit from following a reduced-calorie diet as part of your weight loss plan.
How does Mounjaro dosing differ from Wegovy timing?
Both are once-weekly injections, but Mounjaro (tirzepatide) escalates faster—you may increase doses every 4 weeks up to 15 mg maximum. Wegovy (semaglutide) titrates more gradually to a maximum of 2.4 mg. Both require a clinical assessment and UK prescription before starting, and both work best with consistent weekly timing.
What if I forget my Mounjaro injection?
If you remember within 4 days of your scheduled day, inject as soon as you remember and continue your normal weekly schedule. If more than 4 days have passed, skip that dose and take your next injection on your regular day. Never take a double dose to make up for a missed one.
Can I choose any day of the week for my Mounjaro injection?
Yes—you can choose any day that fits your lifestyle. What's important is consistency. Once you select your day, inject on that same day every week. Your prescriber may recommend a specific day based on your preference and their assessment of your suitability for treatment.
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.