Basal metabolic rate (BMR) calculator

What is basal metabolic rate?

Your Basal Metabolic Rate (BMR) is the number of calories your body uses to maintain basic functions like breathing, circulation and cell repair - even when you're not doing anything at all. It's the foundation of your daily energy needs and an essential first step in managing your weight, planning your nutrition, or understanding your metabolism.

Everyone’s BMR is different. It’s influenced by factors like age, sex, weight, height, and body composition. Knowing your BMR can help you understand how many calories your body needs to function and is especially useful if you're trying to lose, maintain, or gain weight in a healthy way.

BMR is typically estimated using a scientific formula. The most widely accepted method is the Mifflin-St Jeor equation, which provides a reliable estimate based on your physical characteristics.

For men:
BMR = (10 × weight in kg) + (6.25 × height in cm) – (5 × age in years) + 5

For women:
BMR = (10 × weight in kg) + (6.25 × height in cm) – (5 × age in years) – 161

This formula gives you the number of calories your body needs to function at rest. It does not include calories burned through physical activity, which is why BMR is often used as a starting point for calculating your Total Daily Energy Expenditure (TDEE), the full picture of how many calories you burn each day.

Several factors influence your BMR, and understanding them can help you better manage your energy intake and health goals:

• Age – BMR decreases as you get older, due to a natural loss of muscle mass and slower metabolism

• Sex – Men generally have a higher BMR than women, largely because of differences in muscle mass and hormone levels

• Weight and height – Larger individuals tend to have a higher BMR, as their bodies require more energy to function

• Muscle mass – Muscle tissue burns more calories at rest than fat tissue, so individuals with more muscle typically have a higher BMR

• Genetics – Some people are naturally predisposed to have a faster or slower metabolism

• Hormonal conditions – Thyroid function and other hormonal imbalances can significantly affect metabolic rate

• Temperature and environment – Being in cold climates or experiencing fever may increase your BMR as the body works harder to maintain its core temperature

BMR calculators use well-established formulas to provide a close estimate of your resting calorie needs. However, no online calculator can be perfectly accurate because individual metabolism is influenced by many factors, some of which are difficult to measure without medical testing.

To improve accuracy:

• Use your current weight and height

• Choose the formula appropriate for your sex

• Recalculate your BMR as your body changes

• Treat the result as a starting point, not a fixed number

If you're managing a medical condition, or looking for tailored advice about weight loss or nutrition, it's best to speak with a qualified GP, dietitian, or nutrition professional. They can help interpret your BMR in the context of your overall health and lifestyle.