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 — UK Health Information
A weight gain calculator helps you track how much weight you need to gain to reach a healthy weight range for your height. Whether you're underweight, recovering from illness, or building muscle, understanding your target weight is important for your health. In the UK, the NHS uses BMI measurements to define healthy weight ranges, and our free BMI calculator can help you determine whether weight gain would be beneficial for your individual circumstances. This guide explains how to use weight gain calculations, what healthy weight gain looks like, and when to seek GP advice about your weight management goals.
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 Healthy Weight Gain for Your Height
Healthy weight gain depends on your current weight, height, and individual health circumstances. The NHS defines a healthy BMI range as 18.5 to 24.9 for most UK adults. If your BMI is below 18.5, you are classified as underweight, and weight gain may help improve your health outcomes.
To calculate your target healthy weight range, use the formula: healthy weight (kg) = height (metres) squared × BMI (18.5 to 24.9). For example, an adult who is 1.70 metres tall has a healthy weight range of 53.4 kg to 71.7 kg (approximately 8 stone 5 lbs to 11 stone 4 lbs in UK measurements). The difference between your current weight and this range shows how much weight gain would move you into a healthier category.
Use our free BMI calculator and weight converter on this page to instantly calculate your personal healthy weight range in stone, pounds, and kilograms. A GP can provide personalised advice about whether weight gain is appropriate for you, especially if you're recovering from illness or have medical conditions affecting your weight.
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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.
When Weight Gain May Be Recommended
The NHS recommends weight gain in specific situations: underweight status (BMI below 18.5), recovery from illness or surgery, eating disorder recovery, and inadequate nutrition. Underweight individuals face increased health risks including weakened immunity, bone loss, and hormonal imbalances. Safe weight gain typically progresses at 0.5 to 1 kg (1 to 2 lbs) per week, focusing on nutrient-dense foods rather than empty calories.
If you're underweight, your GP can assess whether weight gain is necessary and discuss strategies with you. Registered dietitians can provide personalised nutrition plans. Track your progress using our free progress tracker to monitor steady, healthy weight gain over time. Always consult your GP before starting any weight management programme, especially if you have underlying health conditions.
- 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 is a healthy weight gain rate in the UK?
The NHS recommends gaining 0.5 to 1 kg (1 to 2 lbs) per week for sustainable, healthy weight gain. Faster gains may include excessive fat rather than muscle. Your GP can advise on a safe rate based on your individual circumstances, health status, and reasons for weight gain.
How do I calculate my healthy weight range?
Multiply your height in metres by itself, then multiply by 18.5 (lower limit) and 24.9 (upper limit). For example, at 1.70m tall, your healthy range is 53.4 kg to 71.7 kg. Use our free BMI calculator and weight converter above to calculate instantly in stone, pounds, and kilograms.
Is it unhealthy to be underweight?
Yes. Being underweight (BMI below 18.5) increases risks of weakened immunity, bone loss, hormonal disruption, and nutritional deficiencies. The NHS recommends reaching a healthy weight range. However, always consult your GP before making dietary changes to ensure weight gain is appropriate for you.
Should I see my GP if I want to gain weight?
Yes. A GP assessment is recommended, especially if you're significantly underweight, recovering from illness, or have medical conditions. They can rule out underlying causes, refer you to dietetic services if needed, and provide personalised weight gain guidance safe for your health.
What's the difference between healthy weight gain and unhealthy weight gain?
Healthy weight gain focuses on nutrient-dense foods, progresses gradually (0.5–1 kg/week), and moves you into a healthy BMI range. Unhealthy gain may be too rapid, reliant on processed foods, or exceed healthy targets. A registered dietitian can help you gain weight in the healthiest way for your body composition and wellbeing.
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.