BMR Calculator (Basal Metabolic Rate)
BMR Calculator
Your Basal Metabolic Rate (BMR) is the foundation of all calorie calculations. It tells you the minimum number of calories your body needs each day just to stay alive — before any activity is factored in. Knowing your BMR helps you set realistic calorie targets for weight loss, maintenance, or muscle gain.
Conversion Formula
Mifflin-St Jeor (1990): Male = 10W(kg) + 6.25H(cm) - 5A + 5; Female = 10W(kg) + 6.25H(cm) - 5A - 161. Harris-Benedict (revised 1984): Male = 88.362 + 13.397W(kg) + 4.799H(cm) - 5.677A; Female = 447.593 + 9.247W(kg) + 3.098H(cm) - 4.330A. Imperial inputs are automatically converted to metric before calculation.
Step-by-Step Examples
Male, 30 years, 170 lbs (77 kg), 70 in (178 cm), imperial = Mifflin: 1,740 kcal/day; Harris: 1,885 kcal/day
Mifflin: 10×77.11 + 6.25×177.8 - 5×30 + 5 = 771.1 + 1111.25 - 150 + 5 = 1737 ~ 1,738 kcal. Harris: 88.362 + 13.397×77.11 + 4.799×177.8 - 5.677×30 = 88.36 + 1032.8 + 853.2 - 170.3 = 1804 kcal.
Female, 25 years, 130 lbs (59 kg), 65 in (165 cm), imperial = Mifflin: 1,361 kcal/day; Harris: 1,425 kcal/day
Mifflin: 10×58.97 + 6.25×165.1 - 5×25 - 161 = 589.7 + 1031.9 - 125 - 161 = 1336 kcal. Harris: 447.593 + 9.247×58.97 + 3.098×165.1 - 4.330×25 = 447.6 + 545.3 + 511.4 - 108.3 = 1396 kcal.
Male, 45 years, 85 kg, 180 cm, metric = Mifflin: 1,795 kcal/day; Harris: 1,940 kcal/day
Mifflin: 10×85 + 6.25×180 - 5×45 + 5 = 850 + 1125 - 225 + 5 = 1755 kcal. Harris: 88.362 + 13.397×85 + 4.799×180 - 5.677×45 = 88.4 + 1138.7 + 863.8 - 255.5 = 1835 kcal.
History
The original Harris-Benedict equation was published in 1918-1919. It was revised by Roza and Shizgal in 1984. The Mifflin-St Jeor equation was published in 1990 and validated against indirect calorimetry in multiple studies.
Common Use Cases
- Weight loss calorie targets
- Bulking calorie targets
- Clinical nutrition planning
- Athletic performance nutrition
- Understanding daily energy needs
Frequently Asked Questions
What is BMR?
Basal Metabolic Rate (BMR) is the number of calories your body burns at complete rest — just to maintain basic functions like breathing, circulation, and cell repair. For example, a 30-year-old male who is 5'10" (178 cm) and weighs 170 lbs (77 kg) has a Mifflin BMR of about 1,740 kcal/day.
What is the difference between BMR and TDEE?
BMR is your resting calorie burn. TDEE (Total Daily Energy Expenditure) includes activity. Multiply BMR by an activity factor: 1.2 for sedentary, 1.375 for lightly active, 1.55 for moderately active, 1.725 for very active, and 1.9 for extremely active. A BMR of 1,740 with moderate activity gives a TDEE of about 2,697 kcal/day.
Why do Mifflin and Harris-Benedict give different numbers?
The two formulas use different coefficients derived from different research populations. Mifflin-St Jeor (1990) is generally considered more accurate for modern populations. Harris-Benedict was revised in 1984 but tends to run slightly higher. For a 170 lb, 5'10" 30-year-old male, Mifflin gives ~1,740 and Harris gives ~1,885 kcal/day.
Should I eat at my BMR for weight loss?
Eating exactly at BMR is not recommended for extended periods as it may slow metabolism and cause nutrient deficiencies. Instead, calculate your TDEE and subtract 300-500 calories for a sustainable deficit. Eating below BMR short-term (e.g., 1,200-1,500 kcal) is sometimes done under medical supervision.
Does BMR decrease with age?
Yes. BMR typically decreases by about 1-2% per decade after age 20, largely due to muscle mass loss. A 50-year-old with the same weight and height as a 30-year-old will have a BMR roughly 80-150 kcal/day lower. Strength training helps preserve muscle and slow this decline.