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
Mounjaro Weight Loss by Week — What the Evidence Shows
Weight loss with Mounjaro (tirzepatide) doesn't happen at a fixed rate each week — it's gradual and varies significantly between individuals. Clinical trials show that people using Mounjaro typically experience progressive weight loss over weeks and months as their dose increases, reaching maximum effects around 72 weeks. Most weight loss occurs between weeks 12 and 52. Understanding realistic weekly progress can help you set appropriate expectations and stay motivated throughout your treatment. Use our GLP-1 weight loss calculator to estimate potential results based on your personal situation.
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.
Understanding Mounjaro's Weekly Weight Loss Pattern
Mounjaro works gradually rather than delivering dramatic overnight results. Early weeks (weeks 1–4): Most people experience minimal weight loss in the first 2–4 weeks while taking the 2.5 mg starting dose — typically 0.5–1 kg. Weeks 5–12: As your dose increases to 5 mg and beyond, weight loss accelerates. Many people report losing 1–2 kg per week during this phase, though some experience less. Weeks 12–52: This is when significant cumulative weight loss occurs. Clinical trial data from the SURMOUNT-1 study showed that participants averaged approximately 15–21% total body weight loss by week 72. Important: Individual results vary enormously depending on your starting weight, adherence to diet and exercise, metabolism, and individual response to the medication. Your GPhC-registered prescriber can discuss realistic timelines based on your personal health profile.
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.
Factors Affecting Your Weekly Weight Loss Rate
Several factors influence how much weight you lose each week with Mounjaro. Your current weight: People starting at higher weights often lose more kilograms per week initially. Dose level: The 15 mg maximum dose typically delivers greater weight loss than lower doses, but progression takes time — minimum 4 weeks at each dose level. Diet and exercise: Mounjaro works best alongside a reduced-calorie diet and increased physical activity. Weight loss injections are not a substitute for lifestyle changes. Individual metabolism: Genetic factors, age, and baseline metabolic rate all affect response. Consistency: Missing doses or not following dietary guidance reduces results. Track your progress with our free progress tracker to monitor your weekly changes and identify patterns.
- 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.
How much weight will I lose per week on Mounjaro?
There's no single answer — weekly loss varies from person to person and week to week. Early weeks may show minimal loss; mid-treatment weeks often show 1–2 kg per week. Clinical trials showed an average of 15–clinically studied weight loss over 72 weeks. Your prescriber can discuss realistic expectations based on your individual circumstances.
Why is weight loss slower in the first few weeks?
Weeks 1–4 use the 2.5 mg starter dose, which is lower than therapeutic doses. Your body is also adjusting to the medication. Weight loss accelerates as your dose increases to 5 mg, 7.5 mg, 10 mg, 12.5 mg, and finally 15 mg — with a minimum 4-week interval between increases.
Will I lose the same amount every single week?
No. Weight loss is rarely linear. You may lose 2 kg one week, 0.5 kg the next, then 1.5 kg the following week. Water retention, hormonal cycles, and natural metabolism fluctuations cause this variation. Looking at weekly loss over a 4-week period is more meaningful than daily or single-week changes.
Is weekly weight loss with Mounjaro faster than diet alone?
Clinical trials suggest Mounjaro helps achieve greater weight loss compared to diet and exercise alone. However, Mounjaro is not a replacement for healthy eating and movement — it works alongside these lifestyle changes. Use our BMI calculator to check your baseline, then monitor progress with our free progress tracker.
What if I'm not losing weight every week?
Weight loss plateaus are normal and temporary. If you've not seen progress for 2–3 weeks, discuss this with your prescriber — you may need a dose increase, or your body may simply need time to adjust. Consistency with diet, exercise, and medication timing matters 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.