About the BMR Calculator

Your Basal Metabolic Rate (BMR) is the number of calories your body burns at complete rest just to keep vital functions running — breathing, circulation, cell production, and temperature regulation. It is the biological floor of your calorie needs, and everything else you eat goes toward physical activity and digestion.

Knowing your BMR is the first step in any evidence-based nutrition strategy. Whether you want to lose weight, maintain your current weight, or build muscle, you need to know how many calories your body needs at rest before adding your activity level to find your Total Daily Energy Expenditure (TDEE).

How It Works

Our calculator uses the Mifflin-St Jeor equation — the most clinically validated formula for estimating BMR in healthy adults. It factors in weight, height, age, and biological sex. You then multiply your BMR by an activity multiplier to get your TDEE.

Formula / Key Reference

Mifflin-St Jeor Equation:

Men: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age) + 5
Women: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age) − 161

Activity Multipliers (for TDEE):

Sedentary (desk job, little exercise): BMR × 1.2
Lightly active (exercise 1–3 days/week): BMR × 1.375
Moderately active (exercise 3–5 days/week): BMR × 1.55
Very active (hard exercise 6–7 days/week): BMR × 1.725
Extra active (physical job + hard training): BMR × 1.9

Real-World Example

Person: Male, 35 years old, 180 cm, 85 kg, exercises 4 times per week

BMR = (10 × 85) + (6.25 × 180) − (5 × 35) + 5
= 850 + 1,125 − 175 + 5

= 1,805 calories/day

TDEE (moderately active multiplier 1.55): 1,805 × 1.55 = 2,798 calories/day

To lose 1 lb per week (500 calorie/day deficit): target 2,298 calories/day

To gain 1 lb per week (500 calorie/day surplus): target 3,298 calories/day

Common Uses

  • Setting a calorie target for a structured weight loss or muscle-building plan
  • Comparing how BMR changes with age (it decreases ~2–3% per decade after 30)
  • Adjusting calorie intake after significant weight changes
  • Supporting sports nutrition and performance planning
  • Educational use in nutrition, fitness, and health courses

Frequently Asked Questions

What is the difference between BMR and TDEE? ▼
BMR is the calories burned at complete rest. TDEE is BMR multiplied by an activity factor, representing the total calories burned in a day including exercise, walking, and general movement. You need to know your TDEE to plan a diet.
Which BMR formula is most accurate? ▼
The Mifflin-St Jeor equation is considered the most accurate for most people in clinical research. The older Harris-Benedict equation tends to overestimate by about 5%. For athletes with very high muscle mass, the Katch-McArdle formula (which uses body fat percentage) can be more precise.
Does BMR decrease when I diet? ▼
Yes. When you eat significantly below your TDEE for an extended period, your body can reduce its metabolic rate as an adaptive response — sometimes called 'metabolic adaptation.' This is one reason why gradual calorie reduction (rather than crash dieting) and maintaining muscle through resistance training are important for sustainable fat loss.
How often should I recalculate my BMR? ▼
Recalculate whenever your weight changes by 10 lbs or more, you change your activity level significantly, or after major life events like pregnancy, surgery, or aging a decade. Your BMR is not static.