BMR Calculator

How the BMR Calculator Works

Our BMR calculator estimates your Basal Metabolic Rate — the number of calories your body burns at complete rest — using the Mifflin-St Jeor equation. It then multiplies your BMR by activity factors to show your daily calorie needs (TDEE) across five activity levels, from sedentary to very active.

The Mifflin-St Jeor Equation

This calculator uses the Mifflin-St Jeor equation, which was developed in the 1990s and is considered the most accurate BMR formula for the general population:

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

For a 30-year-old man weighing 70 kg and 175 cm tall, the BMR is 10 × 70 + 6.25 × 175 − 5 × 30 + 5 = 1,621 calories per day. This is the energy his body would burn if he stayed in bed all day — the baseline before any activity is added.

Activity Levels and TDEE

Your Total Daily Energy Expenditure (TDEE) is your BMR multiplied by an activity factor. The five standard activity levels are:

• Sedentary (1.2×): Little or no exercise, desk job.
• Light (1.375×): Light exercise 1–3 days per week.
• Moderate (1.55×): Moderate exercise 3–5 days per week.
• Active (1.725×): Hard exercise 6–7 days per week.
• Very Active (1.9×): Very hard exercise, physical job, or training twice a day.

For the example above, a sedentary lifestyle gives a TDEE of about 1,945 calories, while a very active lifestyle gives about 3,080 calories. The difference shows how much activity contributes to total energy expenditure.

Using BMR for Weight Management

To lose weight, you need to eat fewer calories than your TDEE — a deficit of 500 calories per day typically leads to about 1 pound of weight loss per week. To gain weight, eat more than your TDEE. To maintain your weight, match your intake to your TDEE. Your BMR is the floor: eating below it for extended periods can slow your metabolism and is not recommended without medical supervision.

Factors That Affect BMR

BMR is influenced by age, gender, weight, height, body composition, genetics, and hormones. Muscle tissue burns more calories than fat tissue, so people with more muscle have a higher BMR. BMR tends to decrease with age as muscle mass declines, which is why strength training becomes increasingly important for maintaining metabolism over time.

Tips for Using This Calculator

• Use accurate measurements for weight and height for the best estimate.
• Choose the activity level that matches a typical week, not your best or worst day.
• Use the TDEE that matches your activity as your daily calorie target for maintenance.
• For weight loss, aim for a moderate deficit of 300–500 calories below TDEE.
• Remember that BMR is an estimate — adjust based on real-world results over time.