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
What Weight Loss Can You Expect from Mounjaro in One Month?
Most people starting Mounjaro do not experience significant weight loss in the first month because of how the medication is dosed. Mounjaro is a prescription-only, once-weekly injectable medication that begins at a low starting dose (2.5 mg) and increases gradually every 4 weeks. The first month focuses on your body adjusting to the medication rather than maximum weight loss. Understanding this timeline helps set realistic expectations as you begin your weight management journey with your prescriber.
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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 Dosing Works in Month One
Mounjaro uses a gradual dose titration schedule to help minimise side effects and allow your body to adjust. In your first month, you will receive only the starting dose of 2.5 mg — one injection per week for four weeks.
- Week 1–4: 2.5 mg weekly (starting/adjustment dose)
- Week 5–8: 5 mg weekly (first escalation)
- Week 9–12: 7.5 mg weekly (second escalation)
This means the dose that produces the most significant weight loss effects — the higher doses of 10 mg, 12.5 mg, or 15 mg — is not reached until weeks 13–20+. Clinical evidence shows that meaningful weight loss typically becomes more noticeable from month 2 onwards as your dose increases. A prescriber will only escalate your dose if the current dose is well tolerated.
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.
Realistic Weight Loss Expectations and Timeline
In the first month on Mounjaro at 2.5 mg, weight loss is usually modest or minimal — many people lose little to no weight in week one. Some may experience reduced appetite and lose 1–3 kg by the end of month one, but this is not assured.
Weight loss accelerates as your dose increases. Clinical trial data (SURMOUNT-1) showed that average weight loss of 15–21% of body weight was achieved over 72 weeks at higher maintenance doses (5 mg to 15 mg), combined with a reduced-calorie diet and physical activity. Individual results vary significantly. Use our free BMI calculator and GLP-1 weight loss calculator to track your baseline and project potential outcomes across different dose levels.
- 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.
Will I lose weight in my first month on Mounjaro?
Possibly, but not always significantly. Month one uses the 2.5 mg starting dose, which is lower than therapeutic doses. Many people experience appetite reduction but modest weight loss (0–3 kg). Weight loss typically becomes more noticeable from month 2 onwards as your dose increases.
Why does Mounjaro use such a low starting dose?
The gradual dose titration reduces side effects like nausea and diarrhoea, allowing your body to adjust. It also helps your prescriber identify the right dose for you. The starting dose is not intended for maximum weight loss — it is an adjustment phase.
When will I see real weight loss on Mounjaro?
Most people see more noticeable weight loss from month 2–3 onwards as their dose reaches 5 mg and higher. Clinical trials showed average weight loss of 15–21% over 72 weeks at maximum doses alongside lifestyle changes. Individual timelines vary — discuss expectations with your prescriber.
Is Mounjaro a weekly weight loss injection?
Yes, Mounjaro is injected once per week using a KwikPen device. Each pen contains 4 weekly doses. It is a prescription-only medication licensed for weight management in UK adults with a BMI of 30 or above, or 27–29.9 with weight-related health conditions.
How does Mounjaro compare to Wegovy for weight loss?
Mounjaro (tirzepatide) is a dual GIP + GLP-1 agonist, while Wegovy (semaglutide) is a GLP-1 agonist only. Clinical trials showed Mounjaro achieved average weight loss of 15–21%, while Wegovy achieved approximately 15%. Both require prescription and gradual dose escalation. Individual results vary significantly.
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.