Basal Metabolic Rate (BMR) Calculator (UK)
Understanding Your Basal Metabolic Rate (BMR)
Your Basal Metabolic Rate (BMR) is the number of calories your body needs to perform basic, life-sustaining functions at rest. Think of it as the minimum energy expenditure required to keep your heart beating, lungs breathing, brain functioning, and cells repairing, all while you're completely at rest (like sleeping or sitting perfectly still).
Why is BMR Important?
Understanding your BMR is a fundamental step towards managing your weight and optimising your health. It forms the baseline for your Total Daily Energy Expenditure (TDEE). Your TDEE includes your BMR plus the calories you burn through physical activity, the thermic effect of food (digestion), and other non-exercise activity thermogenesis (NEAT).
- Weight Management: Knowing your BMR helps you create a more accurate calorie deficit for weight loss or a surplus for weight gain.
- Nutrition Planning: It provides a foundation for understanding your overall caloric needs.
- Fitness Goals: When combined with activity levels, BMR helps in setting realistic fitness and performance targets.
How is BMR Calculated?
The most commonly used formulas for calculating BMR are the Harris-Benedict equation and the Mifflin-St Jeor equation. The Mifflin-St Jeor equation is generally considered more accurate for the modern population.
The Mifflin-St Jeor Equation:
This formula is widely recommended:
- 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
Our calculator uses the Mifflin-St Jeor equation to provide you with an estimate of your BMR.
Factors Affecting BMR
Several factors influence your BMR, including:
- Age: BMR typically decreases as you get older, as muscle mass tends to decline.
- Sex: Men generally have a higher BMR than women due to a typically higher muscle mass proportion.
- Body Composition: Muscle tissue burns more calories at rest than fat tissue. Individuals with more muscle mass will have a higher BMR.
- Body Size: Larger bodies require more energy to maintain.
- Genetics: Your genetic makeup can play a role in your metabolic rate.
- Hormones: Thyroid hormones, in particular, significantly impact metabolism.
- Environmental Temperature: Your body expends energy to maintain its core temperature.
Using Your BMR
Once you have your BMR, you can estimate your TDEE by multiplying your BMR by an appropriate activity factor:
- Sedentary: BMR × 1.2 (little or no exercise)
- Lightly Active: BMR × 1.375 (light exercise/sports 1-3 days/week)
- Moderately Active: BMR × 1.55 (moderate exercise/sports 3-5 days/week)
- Very Active: BMR × 1.725 (hard exercise/sports 6-7 days a week)
- Extra Active: BMR × 1.9 (very hard exercise/sports & physical job)
Remember, these are estimates. Individual metabolisms can vary. For precise dietary and fitness advice, consulting a healthcare professional or a registered dietitian is recommended.
Example Calculation:
Let's calculate the BMR for a 35-year-old male who weighs 80 kg and is 180 cm tall.
- Weight: 80 kg
- Height: 180 cm
- Age: 35 years
- Sex: Male
Using the Mifflin-St Jeor formula for men:
BMR = (10 × 80) + (6.25 × 180) – (5 × 35) + 5
BMR = 800 + 1125 – 175 + 5
BMR = 1755 calories per day
This means this individual needs approximately 1755 calories per day just to maintain basic bodily functions at rest.