About This Tool
The BMR (Basal Metabolic Rate) Calculator estimates the number of calories your body burns at complete rest to maintain vital functions like breathing, circulation, and cell production. This is your baseline energy expenditure—the calories you'd burn if you stayed in bed all day. Knowing your BMR is essential for weight management because it helps you determine your total daily energy expenditure (TDEE) when combined with activity level. Common use cases include setting a calorie deficit for weight loss, ensuring you eat enough to avoid metabolic slowdown during dieting, and tailoring nutrition plans for athletes or those with specific fitness goals. The Mifflin-St Jeor equation is considered one of the most accurate formulas for estimating BMR in the general population.
How It Works
The Mifflin-St Jeor equation calculates BMR based on sex, weight, height, and age. For men: BMR = 10 × weight (kg) + 6.25 × height (cm) – 5 × age (y) + 5. For women: BMR = 10 × weight (kg) + 6.25 × height (cm) – 5 × age (y) – 161. The result is in calories per day. For example, a 30-year-old woman weighing 65 kg and 165 cm tall has a BMR of 10×65 + 6.25×165 – 5×30 – 161 = 650 + 1031.25 – 150 – 161 = 1370.25 calories/day.
Examples
- A 45-year-old man who weighs 80 kg and is 178 cm tall: BMR = 10×80 + 6.25×178 – 5×45 + 5 = 800 + 1112.5 – 225 + 5 = 1692.5 calories/day. This is what he burns at rest, so his weight loss diet should not go below this number without medical supervision.
- A 25-year-old woman who weighs 55 kg and is 160 cm tall: BMR = 10×55 + 6.25×160 – 5×25 – 161 = 550 + 1000 – 125 – 161 = 1264 calories/day. She can use this as a baseline to calculate her total needs for maintenance or weight loss.
Pro Tips
- Never eat below your BMR for extended periods—it can slow your metabolism and cause muscle loss. Use BMR as a floor, not a target.
- BMR decreases with age due to muscle loss. Strength training can help preserve or increase muscle mass, keeping your BMR higher.
- For the most accurate BMR estimate, get your body composition tested (e.g., DEXA scan) and use a formula that accounts for lean mass, such as the Katch-McArdle equation.