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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BMI Table With Age — Does Age Change Your Healthy Range?
Many people wonder if their BMI target should change as they get older. The answer is straightforward: the NHS BMI formula and healthy weight ranges remain the same throughout adulthood, regardless of age. However, age does affect how your body composition changes, which is why maintaining a healthy BMI becomes increasingly important as you age. This guide explains the BMI formula, the standard healthy ranges, and why age matters for weight health even though the BMI categories themselves don't shift.
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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.
NHS BMI Categories and How They Apply to All Adults
The BMI formula is age-independent: weight (kg) ÷ height (m)². The NHS BMI range for UK adults—whether you're 25 or 75—remains consistent:
- Underweight: BMI below 18.5
- Healthy weight: BMI 18.5–24.9
- Overweight: BMI 25–29.9
- Obese (Class I): BMI 30–34.9
- Obese (Class II): BMI 35–39.9
- Severely obese: BMI 40+
For people of South Asian, Chinese, Black African, or Black Caribbean heritage, the NHS BMI thresholds are lower—healthy weight starts at 18.5 and overweight begins at 23. These adjustments reflect higher health risks at lower BMI levels for these groups, not age-based changes.
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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.
Why Age Matters for Weight Health—Even If BMI Categories Don't
Although your BMI target doesn't change with age, your body composition does. From around age 30, muscle mass naturally declines (sarcopenia), meaning the same BMI may represent a higher body fat percentage in older adults compared to younger people. This is why maintaining a healthy BMI becomes even more important as you age—and why complementary measures like waist circumference and physical activity matter more. A waist circumference above 94cm for men or 80cm for women signals increased cardiovascular risk, regardless of age. Our free BMI calculator above will give you your personal BMI instantly, and you can use the weight converter to check what your target healthy weight range is in stone and pounds.
- 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 BMI change with age?
No. The BMI formula and healthy weight ranges are the same for adults of all ages. A healthy BMI is 18.5–24.9 for all adults, regardless of whether you're 30 or 80. However, age affects body composition—older adults may have higher body fat at the same BMI due to natural muscle loss.
Should older adults aim for a different BMI range?
No, the NHS BMI categories remain the same. However, older adults should focus on maintaining muscle mass through strength exercise and meeting protein needs, since muscle naturally declines with age. Your GP can give personalised advice for your individual health.
Is BMI less accurate for older people?
BMI has some limitations for all ages, but can be less reliable in older adults because it doesn't distinguish between muscle and fat. An older person with good muscle mass may have a higher BMI but lower health risk than someone younger with the same BMI. Waist circumference measurement provides useful additional context.
What's the difference between BMI and body composition?
BMI measures weight relative to height. Body composition measures the ratio of muscle to fat. Two people with the same BMI can have very different body compositions. As we age, we tend to lose muscle and gain fat, making body composition measurement increasingly important alongside BMI.
Can I use the same BMI target throughout my life?
Yes. A healthy BMI of 18.5–24.9 applies to all adults. However, as you age, also monitor waist circumference (under 94cm for men, 80cm for women), stay physically active to preserve muscle, and discuss any health concerns with your GP for personalised guidance.
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.