BMR Calculator

What is BMR?

Basal Metabolic Rate (BMR) is the number of calories your body needs to perform its most basic life-sustaining functions — breathing, circulation, cell production, nutrient processing, and temperature regulation. It represents the minimum energy expenditure required to keep your body alive while at complete rest.

BMR typically accounts for about 60-75% of your total daily energy expenditure. Even if you spent the entire day lying in bed doing nothing, your body would still burn this many calories just to maintain its vital functions.

How to Use This Calculator

Gender

Select Male or Female. The formula uses a different constant for each (+5 for male, -161 for female).

Age

You can enter your age in two ways:

• Age — Enter your age directly as a number.
• Date of Birth — Enter your birth year, month, and day. The calculator will automatically compute your exact age.

Height & Weight

Use the toggle to switch between unit systems:

• cm / kg — Metric system. Default for most countries.
• ft·in / lb — Imperial system. Default for English (US) users.

All values are automatically converted to metric before the formula is applied.

The Mifflin-St Jeor Equation

This calculator uses the Mifflin-St Jeor equation, which is widely considered the most accurate BMR formula for most people. It was developed by MD Mifflin and ST St Jeor and published in the American Journal of Clinical Nutrition in 1990.

For males:

$BMR = (10 \times weight*{kg}) + (6.25 \times height*{cm}) - (5 \times age\_{years}) + 5$

For females:

$BMR = (10 \times weight*{kg}) + (6.25 \times height*{cm}) - (5 \times age\_{years}) - 161$

The American Dietetic Association (now the Academy of Nutrition and Dietetics) reviewed multiple BMR prediction equations and concluded that the Mifflin-St Jeor equation is the most reliable for estimating resting metabolic rate in both non-obese and obese individuals.

What is TDEE?

Total Daily Energy Expenditure (TDEE) is the total number of calories you burn in a day, including all physical activity. It is calculated by multiplying your BMR by an activity factor:

• Sedentary (x1.2) — Little or no exercise, desk job. Most of the day spent sitting.
• Lightly Active (x1.375) — Light exercise 1-3 days per week. Walking, light stretching, or casual cycling.
• Moderately Active (x1.55) — Moderate exercise 3-5 days per week. Jogging, swimming, or regular gym sessions.
• Very Active (x1.725) — Hard exercise 6-7 days per week. Intense training, competitive sports, or physically demanding job.
• Extra Active (x1.9) — Very hard exercise, physical job, or training twice a day. Professional athletes and heavy manual labor.

How to Use BMR for Weight Management

Understanding your BMR and TDEE is fundamental to managing your weight:

• To lose weight: Eat fewer calories than your TDEE. A deficit of 500 calories per day leads to approximately 0.45 kg (1 lb) of weight loss per week.
• To maintain weight: Eat roughly the same number of calories as your TDEE.
• To gain weight: Eat more calories than your TDEE. A surplus of 250-500 calories per day supports gradual, healthy weight gain.

Important: Never eat below your BMR for extended periods. Going below your basal metabolic rate can slow down your metabolism, cause muscle loss, and lead to nutrient deficiencies. Always aim for a moderate, sustainable deficit above your BMR but below your TDEE.

What Affects BMR?

Several factors influence your Basal Metabolic Rate beyond the inputs in this calculator:

• Muscle mass — Muscle tissue burns more calories at rest than fat tissue. More muscle means a higher BMR.
• Genetics — Some people naturally have a faster or slower metabolism.
• Hormones — Thyroid hormones, in particular, play a major role in metabolic rate.
• Temperature — Exposure to cold can temporarily increase BMR as the body works to maintain its core temperature.
• Age — BMR naturally decreases with age, primarily due to loss of muscle mass.

FAQ

How accurate is the Mifflin-St Jeor equation?

The Mifflin-St Jeor equation is accurate to within about 10% for most people. It is the most reliable predictive equation for healthy adults, but individual variation exists. For precise measurements, indirect calorimetry (a clinical test) is the gold standard.

What is the difference between BMR and RMR?

BMR (Basal Metabolic Rate) is measured under very strict conditions — after fasting for 12 hours, in a darkened room, after 8 hours of sleep. RMR (Resting Metabolic Rate) is measured under less strict conditions and is typically 10-20% higher than BMR. In practice, the terms are often used interchangeably. This calculator estimates BMR, which provides a conservative baseline.

Why does gender affect BMR?

On average, males tend to have more muscle mass and less body fat than females of the same weight, which results in a higher BMR. The +5 (male) and -161 (female) constants in the Mifflin-St Jeor equation account for these average physiological differences.

Should I eat below my BMR to lose weight faster?

No. Eating below your BMR for extended periods can trigger adaptive thermogenesis, where your body slows its metabolism to conserve energy. This makes weight loss harder in the long run and can cause fatigue, hair loss, and hormonal imbalances. A safe approach is to eat between your BMR and TDEE.