BMR Calculator

Basal Metabolic Rate (BMR) is the number of calories your body burns at complete rest to maintain vital functions like breathing, circulation, cell production, and brain activity. It represents roughly 60–70% of your total daily energy expenditure. BMR is most commonly estimated with the Mifflin-St Jeor equation: for men, BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age) + 5; for women, BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age) − 161.

The Mifflin-St Jeor equation (1990) is the current clinical standard and is recommended by the Academy of Nutrition and Dietetics for estimating resting metabolic rate in healthy adults. It is accurate to roughly ±10% for most people and performs better than the older Harris-Benedict equation, especially in overweight and obese populations. The Katch-McArdle formula is more accurate for lean, athletic individuals because it accounts for lean body mass using your body fat percentage.

BMR is the energy your body needs at complete rest. Total Daily Energy Expenditure (TDEE) is your BMR multiplied by an activity factor that accounts for exercise, walking, and daily movement. TDEE = BMR × activity multiplier, where multipliers range from 1.2 (sedentary) to 1.9 (extra active). TDEE is the true number of calories you burn in a day — eat at this level to maintain weight, below it to lose, and above it to gain.

A calorie deficit of roughly 500 kcal per day below your TDEE typically results in about 0.5 kg (1 lb) of fat loss per week, while a surplus of 300–500 kcal supports gradual muscle gain. Your BMR is the absolute floor of your energy needs — clinical guidelines generally recommend never eating below your BMR without medical supervision, as this can slow metabolism and cause muscle loss. Use your BMR to understand your baseline, and your TDEE to plan intake.

BMR declines roughly 1–2% per decade after age 20, primarily because lean muscle mass (the most metabolically active tissue) decreases with age while fat mass tends to increase. Muscle burns about 13 kcal per kg per day at rest, compared to about 4.5 kcal for fat. Strength training preserves muscle and can substantially slow this decline — which is why two people of the same weight and height can have very different BMRs.

Yes. The Mifflin-St Jeor equation includes a constant of +5 kcal for men and −161 kcal for women. On average, women have a 5–10% lower BMR than men of the same age, height, and weight, primarily because they typically carry a higher percentage of body fat and less lean mass. When normalized for lean body mass, the difference largely disappears.

BMR (Basal Metabolic Rate) is measured under strict conditions: immediately after waking, 12 hours after eating, in a thermoneutral environment, at complete physical and mental rest. RMR (Resting Metabolic Rate) is measured under less strict conditions — after 3–4 hours of fasting and some rest — and is typically 10–20% higher than BMR. For practical purposes, the two are used interchangeably, and most online calculators estimate RMR while calling it BMR.

Yes. The calculator is 100% free with no registration, and every calculation runs entirely in your browser using JavaScript — no data is ever sent to a server. If you choose to save results, they are stored only in your browser's localStorage, and you can export, import, or clear your history at any time.