BMI, BMR & Calorie Calculator UK

Clinical context

What BMI means for weight loss treatment in the UK

BMI (body mass index) is a quick screening number—weight relative to height. It does not measure body fat directly, but UK clinicians often use it alongside your history to think about Wegovy, Mounjaro, and other options. Our tool helps you estimate BMI and understand typical private eligibility bands—not to replace a consultation.

BMI requirement for Wegovy and Mounjaro (typical UK framing)

• BMI 30 or above (obesity): often the clearest group for discussing GLP-1 weight loss medicines privately, assuming no contraindications.
• BMI 27–29.9 (overweight): treatment may be considered when weight-related health conditions are present (for example, high blood pressure, dyslipidaemia, obstructive sleep apnoea, or prediabetes)—your prescriber decides.
• Under BMI 27: prescription weight loss injections are usually not the first option; lifestyle change and broader medical review tend to lead.

If you are asking am I eligible for Wegovy in the UK, the answer always depends on a full assessment—BMI is only one part. See Wegovy eligibility (UK) and Mounjaro eligibility (UK) on our guides for detail.

What is BMI?

BMI compares your weight to your height using the formula weight ÷ height² (with height in metres and weight in kilograms). It is widely used because it is simple and consistent, which helps public health and clinical pathways talk about risk at a population level.

For individuals, BMI is a starting point: athletes with high muscle mass, some older adults, and certain ethnic groups may need different interpretations—your clinician may also look at waist size, blood tests, medications, and medical history.

BMI and weight loss treatment in the UK

Prescription medicines such as Wegovy and Mounjaro are not bought off the shelf: a qualified prescriber must review risks and benefits. BMI thresholds help triage who might be suitable, especially in private services that mirror NICE-style criteria, but they never tell the whole story.

When you are ready to compare pathways and monthly costs, our Wegovy vs Mounjaro page and cheapest options UK hub connect research to action—always alongside professional advice.

Is BMI accurate?

BMI is accurate for what it is designed to do: summarise weight-for-height. It is not accurate as a personal body fat measurement, and it can misclassify muscular people as overweight or miss risk in people with higher visceral fat at a "healthy" BMI.

Reliable decisions about GLP-1 treatment rely on a prescriber's judgement, monitoring, and your follow-up—not on any online calculator alone. Use this page to learn and prepare questions; use appointments to decide.

FAQ

BMI & UK weight loss treatment

What is a healthy BMI in the UK?

For most UK adults, a BMI between 18.5 and 24.9 is considered a healthy weight range. Below 18.5 is underweight; 25 to 29.9 is overweight; 30 or above is obese. BMI is a screening tool—not a diagnosis—and doesn't account for muscle mass or where fat is stored.

What BMI qualifies for Wegovy in the UK?

Private prescribing in the UK often follows similar bands to clinical guidance: typically BMI 30 or above, or BMI 27 or above with weight-related health conditions. Only a qualified prescriber can confirm eligibility after reviewing your medical history, medications, and goals.

Is BMI enough to get weight loss treatment?

No. BMI helps triage who might be suitable, but treatment decisions require a full assessment: conditions like diabetes, thyroid disorders, pregnancy, medicines you take, mental health, and more. You should never start prescription injections without clinician supervision.

What BMI is needed for Mounjaro in the UK?

Like other GLP-1-based weight loss medicines, Mounjaro is generally considered for adults with obesity (often BMI 30+) or overweight (often BMI 27+) when certain health conditions apply. NICE recommendations and individual providers may differ—your prescriber interprets what's appropriate for you.

BMR & TDEE (metabolism & calories)

What is BMR (Basal Metabolic Rate)?

BMR is an estimate of how many calories your body burns at complete rest—before daily activity, digestion, or exercise. It reflects energy needed for breathing, circulation, cell repair, and other basic functions. It is not the same as how much you should eat in a day; that is closer to TDEE (total daily energy expenditure).

How does Health Wise calculate BMR?

We use the Mifflin–St Jeor equation, a widely used formula that takes your weight, height, age, and sex. Like all estimates, it can differ from lab-measured metabolic rate—muscle mass, genetics, thyroid health, and medications can shift real energy needs. Use the number as a planning guide, not a prescription.

What is TDEE (Total Daily Energy Expenditure)?

TDEE is an estimate of how many calories you burn across a whole day, including BMR plus the energy from movement, work, fidgeting, digestion, and exercise. Our calculator multiplies your BMR by an activity factor (from sedentary to very active). Pick the level that best matches your typical week, not your best week.

What is the difference between BMR and TDEE?

BMR is rest-only; TDEE adds everything you do on top of that. If you ate exactly your BMR every day while still walking, working, and training, you would usually be in a large deficit because TDEE is higher. For weight planning, TDEE (or a clinician’s plan) is usually the more relevant starting point than BMR alone.

How accurate are BMR and TDEE calculators?

They are reasonable population averages, not personalised medical tests. Error margins of roughly 10–20% are common. Athletes, very lean or very muscular people, older adults, and those on certain drugs (including some GLP-1 medicines) may sit above or below the estimate. Treat outputs as discussion points with a dietitian, GP, or prescriber—not rigid targets.

Should I follow TDEE calorie targets if I am on Wegovy or Mounjaro?

GLP-1 treatments often reduce appetite naturally, so fixed calorie numbers from any online calculator may not match how you feel or what your clinician wants. Some people need structured minimum intakes for health; others need adjustments for muscle or medical conditions. Always follow the eating plan agreed with your healthcare team rather than a generic deficit from a website.