BMR Calculator

What is BMR Calculator?

A BMR (Basal Metabolic Rate) Calculator estimates the calories your body needs to maintain basic physiological functions at complete rest — breathing, circulation, cell production, body temperature regulation, and nutrient processing. For most people, BMR accounts for roughly 60-75% of all calories burned in a day, making it the largest component of your energy budget.

This free BMR calculator uses the Mifflin-St Jeor equation, published in 1990 and recommended by the Academy of Nutrition and Dietetics as the most reliable predictive formula for healthy adults. Multiplying your BMR by an activity factor gives your Total Daily Energy Expenditure (TDEE), the starting point for any weight or nutrition plan.

How to Use

1. Select your gender and unit system (Metric or Imperial).
2. Enter your age, height, and weight; Imperial values are converted to metric automatically.
3. Click Calculate BMR to see your basal metabolic rate, rounded to the nearest calorie.
4. Check the activity table for estimated daily calorie needs at five activity levels.

The Mifflin-St Jeor BMR Formula

The calculator applies a gender-specific constant:

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

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

• BMR — the result, in kilocalories (kcal) per day.
• Weight — body mass in kilograms (1 lb = 0.45359237 kg).
• Height — standing height in centimeters (1 inch = 2.54 cm).
• Age — each additional year subtracts 5 kcal per day.
• +5 / −161 — the gender constant, reflecting average differences in body composition.

Alternative BMR Formulas

Two other equations are widely used. The revised Harris-Benedict equation (1984) tends to estimate slightly higher:

Men: BMR = 88.362 + (13.397 × weight) + (4.799 × height) − (5.677 × age)

Women: BMR = 447.593 + (9.247 × weight) + (3.098 × height) − (4.330 × age)

The Katch-McArdle formula uses lean body mass instead of total weight, so it is identical for both sexes but requires your body fat percentage:

BMR = 370 + (21.6 × lean body mass in kg), where lean body mass = weight × (1 − body fat %).

If you do not know your body fat percentage, estimate it with our Body Fat Calculator. Katch-McArdle is often the best choice for very lean or muscular people, whose composition differs most from the averages behind Mifflin-St Jeor.

BMR Calculation Example

Take a 40-year-old man, 85 kg and 178 cm tall, and work through the Mifflin-St Jeor equation:

• Weight term: 10 × 85 = 850
• Height term: 6.25 × 178 = 1,112.5
• Age term: 5 × 40 = 200
• BMR = 850 + 1,112.5 − 200 + 5 = 1,767.5 ≈ 1,768 kcal/day

A woman with identical stats uses −161 instead of +5, giving 1,601.5 ≈ 1,602 kcal/day. For comparison, revised Harris-Benedict gives 1,854 kcal and Katch-McArdle (at 20% body fat, 68 kg lean mass) gives 1,839 kcal — all in a similar range.

Applying the activity multipliers from the results table above, this man's estimated daily needs are 2,122 kcal sedentary, 2,740 kcal moderately active, and 3,359 kcal with a physical job or heavy training.

BMR Reference Table

Mifflin-St Jeor values (kcal/day) for representative builds at four ages — note that BMR falls by 50 kcal per decade at any fixed size.

BMR vs. RMR vs. TDEE

These terms are often confused. BMR is measured under strict laboratory conditions: after a full night's sleep, a 12-hour fast, and complete rest. RMR (Resting Metabolic Rate) is measured more loosely and runs a few percent higher, since it includes small costs like digestion and posture. In everyday use the two are nearly interchangeable.

TDEE (Total Daily Energy Expenditure) is the practical number: your BMR multiplied by an activity factor, covering everything you burn in a normal day. Get it directly with our TDEE Calculator, then plan intake with the Calorie Calculator.

Why BMR Drops With Age

Resting metabolism declines steadily through adulthood, which the equations capture with the −5 kcal per year term. The main driver is sarcopenia — the loss of 3-8% of muscle mass per decade after age 30 — because muscle burns more calories at rest than fat. Hormonal changes and a small decline in organ metabolic rates also contribute.

Using BMR for Weight Loss or Gain

Your BMR is a floor, not a target. Eating below it for extended periods can trigger muscle loss, fatigue, and metabolic adaptation. Instead, start from your TDEE:

• Weight loss: eat 250-500 kcal below your TDEE to lose roughly 0.25-0.5 kg (0.5-1 lb) per week.
• Weight gain: eat 250-500 kcal above your TDEE, combined with strength training, to gain mostly lean tissue.
• Maintenance: eat at your TDEE and recalculate every few months, since BMR shifts with weight and age.

Frequently Asked Questions