BMR Calculator UK
Calculate your Basal Metabolic Rate (calories burned at rest) using the Mifflin–St Jeor formula.
How it works
BMI compares your weight to your height as a general screening number. It is the same formula worldwide; only the units differ.
BMI = weight (kg) ÷ height (m)²- Under 18.5 = underweight
- 18.5–24.9 = healthy
- 25–29.9 = overweight
- 30+ = obese
Frequently asked questions
What is BMR?
Basal metabolic rate is the number of calories your body uses at rest to maintain basic functions like breathing and circulation, before any physical activity.
How is BMR calculated?
This calculator uses the Mifflin-St Jeor equation, which estimates BMR from your weight, height, age and sex.
What is the difference between BMR and RMR?
They are very close. BMR is measured under strict resting conditions, while resting metabolic rate (RMR) is measured under slightly less restrictive conditions and is usually a little higher.
What lowers or raises BMR?
More lean muscle and larger body size tend to raise it; ageing and muscle loss tend to lower it. Sex, genetics and hormones also influence it.
How accurate is a BMR estimate?
It is a population-based estimate and can differ from your true value, which only lab testing measures. Treat it as a general reference, not an exact figure.
Is this medical advice?
No. It is for general education only. For advice specific to your health or nutrition, consult a qualified healthcare professional.
What basal metabolic rate means
Your basal metabolic rate (BMR) is the energy your body uses at complete rest just to keep essential functions running — breathing, circulation, organ function and maintaining body temperature. It typically accounts for the majority of the calories a person uses in a day, before any activity is added.
How it is calculated
This tool uses the Mifflin-St Jeor equation, which research generally finds the most accurate for the population. For men: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age) + 5. For women the final term is −161 instead of +5. The result is an estimate of resting calorie use per day.
What affects your BMR
BMR tends to be higher with more lean muscle mass and larger body size, and it generally declines with age as muscle is lost. Sex, genetics, hormones and some medical conditions also play a role, which is why two people of the same weight can have different rates.
Using the number sensibly
BMR is an estimate, not a precise measurement — only lab testing measures it directly. It is most useful as a general reference point for understanding energy needs. For guidance tailored to your health, body composition or any medical condition, speak with a doctor or registered dietitian.
Results are estimates for general guidance in United Kingdom and may not reflect the latest local rates, fees or rules. Check official sources before making decisions.