BMR Calculator
Calculates the calories your body burns at complete rest using the Mifflin-St Jeor equation. Use it as the starting point for any diet or fitness plan.
About this calculator
Basal Metabolic Rate (BMR) is the number of calories your body needs to sustain basic life functions — breathing, circulation, and cell production — while at complete rest. This calculator uses the Mifflin-St Jeor equation, widely regarded as the most accurate formula for the general population. For males: BMR = 88.362 + (13.397 × weight_kg) + (4.799 × height_cm) − (5.677 × age). For females: BMR = 447.593 + (9.247 × weight_kg) + (3.098 × height_cm) − (4.330 × age). These coefficients reflect the differing metabolic rates between biological sexes. Knowing your BMR lets you calculate how many calories you need each day — whether your goal is weight loss, maintenance, or muscle gain. It forms the foundation for TDEE and calorie deficit calculations.
How to use
Suppose you are a 30-year-old male weighing 80 kg and standing 175 cm tall. Plug into the male formula: BMR = 88.362 + (13.397 × 80) + (4.799 × 175) − (5.677 × 30). Step by step: 13.397 × 80 = 1,071.76; 4.799 × 175 = 839.825; 5.677 × 30 = 170.31. Sum: 88.362 + 1,071.76 + 839.825 − 170.31 = 1,829.64 calories/day. This means your body burns roughly 1,830 calories per day at rest.
Frequently asked questions
What is BMR and why does it matter for weight loss?
BMR stands for Basal Metabolic Rate — the number of calories your body burns just to stay alive at complete rest. It accounts for roughly 60–70% of your total daily calorie burn. Knowing your BMR matters because eating below it for extended periods can slow metabolism and cause muscle loss. It is the essential baseline from which all calorie targets for weight loss or gain are calculated.
How accurate is the Mifflin-St Jeor equation compared to other BMR formulas?
The Mifflin-St Jeor equation is consistently rated the most accurate BMR formula for most adults in peer-reviewed studies, outperforming the older Harris-Benedict equation by about 5%. However, it still carries a margin of error of roughly ±10% because it does not account for body composition — a muscular person will have a higher BMR than a sedentary person of the same weight. For greatest precision, a DEXA scan or metabolic test can be used.
When should I recalculate my BMR?
You should recalculate your BMR whenever your weight changes by more than 2–3 kg, you have a significant birthday (age affects the formula), or your fitness level changes substantially over several months. BMR naturally declines with age, roughly 1–2% per decade after age 20. Regular recalculation ensures your calorie targets remain accurate and your diet or fitness plan stays effective.