Health & Fitness
BMR Calculator
Calculate your Basal Metabolic Rate (BMR) to determine the number of calories your body burns at rest.
Reviewed by the calculator.uk.com Team · Last reviewed 15 June 2026 · Our methodology
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Related to BMR Calculator
The BMR (Basal Metabolic Rate) calculator uses two widely accepted scientific equations to estimate the number of calories your body burns at complete rest. These equations take into account your age, gender, height, and weight to provide accurate estimates of your daily basal energy expenditure.
Mifflin-St Jeor Equation
This is the primary equation used in our calculator, as it's considered the most accurate for modern populations. For men: BMR = (10 × weight) + (6.25 × height) - (5 × age) + 5. For women: BMR = (10 × weight) + (6.25 × height) - (5 × age) - 161.
Harris-Benedict Equation
This is the original BMR equation, still widely used in clinical settings. For men: BMR = 66.47 + (13.75 × weight) + (5.003 × height) - (6.755 × age). For women: BMR = 655.1 + (9.563 × weight) + (1.850 × height) - (4.676 × age).
Your BMR represents the minimum number of calories your body needs to maintain basic life functions like breathing, circulation, and cell production. This number serves as a baseline for understanding your daily caloric needs and can be used to develop effective nutrition and weight management strategies.
Total Daily Energy Expenditure (TDEE)
To estimate your total daily calorie needs, multiply your BMR by an activity factor: • Sedentary (little/no exercise): BMR × 1.2 • Lightly active (1-3 days/week): BMR × 1.375 • Moderately active (3-5 days/week): BMR × 1.55 • Very active (6-7 days/week): BMR × 1.725 • Extra active (athletes): BMR × 1.9
1. Why do I get two different BMR results?
The calculator provides results from both the Mifflin-St Jeor and Harris-Benedict equations. The Mifflin-St Jeor equation is generally considered more accurate for modern populations, while the Harris-Benedict equation is still widely used in clinical settings. The difference between the results is typically small, and both provide valid estimates.
2. How can I use my BMR for weight management?
Your BMR helps determine your daily caloric needs. For weight loss, consume fewer calories than your total daily energy expenditure (TDEE). For weight gain, consume more. A safe caloric deficit or surplus is typically 500 calories per day, which can lead to about 1 pound (0.45 kg) of weight change per week.
3. Why does BMR decrease with age?
BMR typically decreases with age due to several factors: loss of muscle mass (which burns more calories than fat), hormonal changes, and reduced cellular activity. This is why both equations include age as a factor in their calculations.
4. How often should I recalculate my BMR?
It's recommended to recalculate your BMR whenever there are significant changes in your weight (more than 10 pounds/4.5 kg), after major lifestyle changes, or approximately every 6 months. Regular recalculation helps maintain accurate estimates of your caloric needs.
5. What is the scientific source for this calculator?
Two independent equations are used side by side here: Mifflin-St Jeor, published by Mark Mifflin and Sachiko St Jeor in 1990, and the older Harris-Benedict equation, first published in 1918 and revised in 1984. Both were derived from measured resting energy expenditure in study populations and remain standard tools in clinical and sports nutrition. Mifflin-St Jeor is generally regarded as the better fit for contemporary populations, which is why it is preferred in more recent dietetics guidance, but Harris-Benedict is still referenced in many clinical settings.