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 To Inject Mounjaro — Timing & Scheduling
There is no single "best time" to inject Mounjaro — what matters most is choosing a day and time you can remember each week, and sticking to it consistently. Mounjaro is a once-weekly tirzepatide injection, and consistency is far more important than the time of day. Many people inject on the same day each week (for example, every Monday morning), but your body's response depends on maintaining that regular rhythm, not on whether you inject in the morning, afternoon, or evening.
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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.
Weekly Injection Consistency & Timing Guidelines
Mounjaro is injected once every seven days — the exact time of day is entirely your choice. However, consistency matters. Here's what you need to know:
- Pick a day and stick to it: Choose the same day each week. Many people inject on a Monday, but any day works. Set a phone reminder to help.
- Timing flexibility: Morning, afternoon, or evening injections all work equally well. The medication does not depend on circadian timing.
- Time window: If you miss your usual time, you have flexibility — you can inject within a few hours of your scheduled time without affecting dose effectiveness.
- Missed dose: If you miss an injection, take it within 4 days of the missed dose and resume your normal weekly schedule. If it's been more than 4 days, skip that dose and inject on your next regular day.
Practical tip: Many people find it helpful to inject on the same day as another weekly routine — for example, Sunday evening with meal prep, or Monday morning before work. This makes it easier to remember.
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 Affects Mounjaro Effectiveness — Beyond Timing
While injection timing is flexible, several factors do affect how well Mounjaro works for you:
- Dose consistency: Taking your dose every week (not skipping weeks) is far more important than the time of day.
- Storage: Keep unopened KwikPens refrigerated at 2–8°C. After first use, pens can be kept at room temperature (below 30°C) for up to 30 days.
- Injection technique: Rotate injection sites weekly between your stomach, upper thigh, or upper arm to avoid lipohypertrophy (thickened skin).
- Lifestyle factors: Mounjaro works best alongside a reduced-calorie diet and increased physical activity — medication alone does not produce results.
Try our GLP-1 weight loss calculator to estimate your potential results when combining Mounjaro with lifestyle changes.
- 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 effectiveness does not depend on the time of day. What matters is choosing a consistent day each week and sticking to it. Morning, afternoon, or evening injections all work equally well. Pick a time that fits your routine and you're likely to remember.
Can I change my injection day if I miss my usual time?
You can inject within a few hours of your normal time without issues. If you miss your full weekly dose, inject within 4 days of the missed dose and continue your normal schedule. If more than 4 days have passed, skip that dose and inject on your next scheduled day. Never take a double dose.
What's the minimum time between Mounjaro injections?
The minimum time between doses is 72 hours (3 days). Mounjaro is designed for once-weekly dosing — do not inject more frequently. If you inject early, you may need to adjust your schedule to maintain the 7-day pattern.
Does Mounjaro work differently if I inject in the morning versus evening?
No. Clinical trials and real-world data show no difference in effectiveness between morning and evening injections. Your body responds to the consistent weekly dose, not the time of day. Choose whatever time suits your lifestyle.
Should I inject Mounjaro before or after eating?
Mounjaro works the same whether you eat before or after injection. You can eat normally on injection day. However, many people find it easier to remember their injection if they pair it with a routine — for example, Sunday evening or Monday morning — regardless of meal timing.
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.