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
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Weight Gain Calculator — Understanding Your Weight Changes
A weight gain calculator helps you track how your weight is changing over time and understand what those changes mean for your health. Whether you're noticing gradual weight increases or sudden changes, knowing your current weight, BMI, and healthy weight range according to NHS guidance is the first step. This guide explains how to calculate and interpret weight gain, and how it relates to your overall health and wellbeing.
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.
How to Calculate and Track Weight Changes
Tracking weight gain is straightforward: measure your current weight and compare it to a previous measurement. The difference is your weight gain. However, understanding what that means requires context: weight change depends on multiple factors including age, activity level, metabolism, medical conditions, and medications.
- Weigh yourself at the same time each day (ideally morning before eating)
- Use the same scales for consistency
- Record measurements weekly rather than daily (daily fluctuations are normal)
- Compare trends over weeks or months, not individual days
Use our free progress tracker to log your weight measurements automatically and visualize patterns over time. Our BMI calculator also helps you understand where your current weight falls within NHS healthy weight ranges, giving you actionable context beyond just the number on the scales.
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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.
What Constitutes Healthy vs. Unhealthy Weight Gain
Healthy weight gain occurs at approximately 0.5–1 kg per week during intentional muscle-building with resistance exercise, or during pregnancy (typically 11–16 kg total). Unintended weight gain — particularly more than 1 kg per week without medical explanation — may warrant investigation.
Use our free BMI calculator to determine your current BMI category according to NHS guidelines (healthy weight is BMI 18.5–24.9). Our weight converter helps you understand your weight in both kg and stone, which is essential for NHS health guidance. If you notice rapid weight gain, changes in appetite, fatigue, or other health symptoms, discuss these with your GP — they can assess whether underlying medical conditions are contributing.
- 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.
What counts as significant weight gain?
Weight gain of more than 1–2 kg per week without intentional exercise or dietary changes, or persistent unexplained weight gain despite maintaining previous habits, warrants GP investigation. Sudden changes can indicate metabolic, hormonal, or medication-related causes.
How do I track weight gain accurately?
Weigh yourself at the same time daily (preferably morning), use the same scales, and record weekly averages rather than daily measurements. Track over weeks or months to spot trends. Our free progress tracker automates this logging.
Is all weight gain bad for health?
No. Weight gain from muscle building during exercise is healthy. Gradual weight gain in pregnancy is expected. However, persistent weight gain increasing your BMI into overweight or obese categories is associated with increased health risks according to NHS guidance.
When should I contact my GP about weight gain?
Contact your GP if you experience rapid unexplained weight gain, weight gain alongside fatigue or appetite changes, weight gain after starting new medication, or if your BMI enters a higher health risk category. Your GP can assess underlying causes.
How is weight gain related to BMI changes?
Weight gain directly affects your BMI (weight in kg divided by height in metres squared). Even small weight gains can shift your BMI category — for example, gaining 5 kg might move you from healthy weight to overweight. Use our BMI calculator to check how weight changes affect your category.
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.