BMR Calculator - Free Online Tool

Calculate your Basal Metabolic Rate and daily calorie needs using scientifically validated formulas

Welcome to our free BMR (Basal Metabolic Rate) Calculator, a comprehensive tool that estimates the number of calories your body burns at rest to maintain essential life functions such as breathing, blood circulation, cell production, and nutrient processing. Your BMR represents the minimum amount of energy your body needs to function while at complete rest. This calculator uses two of the most trusted formulas in nutritional science: the Mifflin-St Jeor equation (developed in 1990 and considered the most accurate by the American Dietetic Association) and the classic Harris-Benedict equation (originally developed in 1919 and revised in 1984). By showing results from both formulas side by side, you can get a more complete picture of your metabolic rate. Your BMR is influenced by several factors including age, gender, weight, and height. Men typically have a higher BMR than women due to greater muscle mass. BMR also decreases with age as muscle mass naturally declines. Taller and heavier individuals generally have higher BMRs because their bodies require more energy to maintain. Beyond your BMR, this calculator also computes your Total Daily Energy Expenditure (TDEE) by factoring in your activity level. Your TDEE represents the total number of calories you burn in a day, including exercise and daily activities. This is the number you should use when planning your diet, whether your goal is weight loss, maintenance, or muscle gain. The calculator provides practical calorie targets: a 500-calorie daily deficit for gradual weight loss (approximately 1 pound per week) and a 500-calorie surplus for weight gain. It also includes a suggested macronutrient breakdown showing recommended grams of protein, carbohydrates, and fat based on a balanced 30/40/30 split. All calculations are performed instantly in your browser. No personal data is stored or transmitted to any server, ensuring your complete privacy. Whether you are starting a new diet plan, training for a sport, or simply curious about your metabolism, this calculator gives you the science-backed numbers you need to make informed decisions about your nutrition.

Understanding Basal Metabolic Rate

Your Basal Metabolic Rate (BMR) is the number of calories your body burns at complete rest over a 24-hour period. It accounts for 60-75% of your total daily calorie expenditure.

The Mifflin-St Jeor Equation

Developed in 1990, the Mifflin-St Jeor equation is considered the most accurate BMR formula by the American Dietetic Association. For men: BMR = 10 x weight(kg) + 6.25 x height(cm) - 5 x age + 5. For women: BMR = 10 x weight(kg) + 6.25 x height(cm) - 5 x age - 161.

The Harris-Benedict Equation

Originally published in 1919 and revised in 1984, the Harris-Benedict equation is the classic BMR formula. For men: BMR = 88.362 + 13.397 x weight(kg) + 4.799 x height(cm) - 5.677 x age. For women: BMR = 447.593 + 9.247 x weight(kg) + 3.098 x height(cm) - 4.330 x age.

Formulas

Mifflin-St Jeor (Men)

BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age + 5

Developed in 1990, considered the most accurate BMR formula by the American Dietetic Association. Recommended for the general population.

Mifflin-St Jeor (Women)

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

Female version of the Mifflin-St Jeor equation, which uses a constant of −161 instead of +5 to account for lower average lean mass in women.

Revised Harris-Benedict (Men)

BMR = 88.362 + 13.397 × weight(kg) + 4.799 × height(cm) − 5.677 × age

Updated in 1984 by Roza and Shizgal from the original 1919 formula. Uses revised coefficients for improved accuracy.

Revised Harris-Benedict (Women)

BMR = 447.593 + 9.247 × weight(kg) + 3.098 × height(cm) − 4.330 × age

Female version of the revised Harris-Benedict equation with gender-specific coefficients.

Katch-McArdle

BMR = 370 + 21.6 × lean body mass(kg)

Uses lean body mass (fat-free mass) instead of total weight. More accurate for lean or muscular individuals. Requires body fat percentage input.

Reference Tables

Typical BMR Ranges by Age and Sex

Average basal metabolic rate ranges in calories per day for adults of average weight and height

Age Group	Men (cal/day)	Women (cal/day)
18–25	1,700–1,900	1,350–1,550
26–35	1,600–1,800	1,300–1,500
36–45	1,550–1,750	1,250–1,450
46–55	1,500–1,700	1,200–1,400
56–65	1,400–1,650	1,150–1,350
66+	1,300–1,550	1,100–1,300

Activity Level Multipliers (TDEE = BMR × Factor)

Multiply your BMR by the appropriate factor to estimate total daily energy expenditure

Activity Level	Factor	Description
Sedentary	1.2	Little or no exercise, desk job
Lightly Active	1.375	Light exercise 1–3 days/week
Moderately Active	1.55	Moderate exercise 3–5 days/week
Very Active	1.725	Hard exercise 6–7 days/week
Extra Active	1.9	Very hard daily exercise or physical job

Worked Examples

Example 1: Mifflin-St Jeor for a Male

A 30-year-old male, weight 80 kg (176 lbs), height 178 cm (5'10"), moderately active.

BMR = 10 × 80 + 6.25 × 178 − 5 × 30 + 5

BMR = 800 + 1,112.5 − 150 + 5 = 1,767.5 cal/day

TDEE = BMR × 1.55 (moderately active) = 1,767.5 × 1.55 = 2,740 cal/day

Weight loss target = TDEE − 500 = 2,240 cal/day

BMR is 1,768 cal/day, TDEE is 2,740 cal/day, and the weight loss target (1 lb/week) is 2,240 cal/day.

Example 2: Harris-Benedict for a Female

A 45-year-old female, weight 65 kg (143 lbs), height 165 cm (5'5"), lightly active.

BMR = 447.593 + 9.247 × 65 + 3.098 × 165 − 4.330 × 45

BMR = 447.593 + 601.055 + 511.17 − 194.85 = 1,364.97 cal/day

TDEE = BMR × 1.375 (lightly active) = 1,365 × 1.375 = 1,877 cal/day

BMR is approximately 1,365 cal/day and TDEE is approximately 1,877 cal/day.

Example 3: Katch-McArdle for an Athlete

A 28-year-old male, weight 85 kg, body fat 12%.

Lean body mass = 85 × (1 − 0.12) = 85 × 0.88 = 74.8 kg

BMR = 370 + 21.6 × 74.8 = 370 + 1,615.68 = 1,985.68 cal/day

BMR using Katch-McArdle is approximately 1,986 cal/day, higher than standard formulas would estimate due to high lean mass.

How to Use the BMR Calculator

Enter Your Personal Details

Select your gender and enter your age. Gender affects BMR because men typically have more muscle mass than women, which burns more calories. Age matters because metabolism naturally slows as you get older.

Enter Your Height and Weight

Choose between imperial (lbs, feet/inches) or metric (kg, cm) units, then enter your current weight and height. These measurements are the primary factors in the BMR equations.

Select Your Activity Level

Choose the activity level that best matches your typical week. Options range from Sedentary (desk job, no exercise) to Extra Active (intense daily exercise or physical labor). Be honest to get accurate TDEE results.

Review Your BMR and TDEE Results

View your BMR from both the Mifflin-St Jeor and Harris-Benedict formulas, your TDEE (total calories burned daily), and calorie targets for weight loss or gain. The macronutrient breakdown shows suggested daily protein, carb, and fat intake in grams.

Frequently Asked Questions

What is the difference between BMR and TDEE?

BMR (Basal Metabolic Rate) is the number of calories your body burns at complete rest just to maintain basic life functions like breathing, circulation, and cell repair. It represents your body's minimum energy requirement if you stayed in bed all day. TDEE (Total Daily Energy Expenditure) is your BMR multiplied by an activity factor that accounts for exercise and daily movement. TDEE represents the total calories you actually burn in a day. For example, if your BMR is 1,600 calories and you are moderately active (multiplier of 1.55), your TDEE would be approximately 2,480 calories. You should use TDEE, not BMR, when planning your daily calorie intake.

Which BMR formula is more accurate - Mifflin-St Jeor or Harris-Benedict?

The Mifflin-St Jeor equation is generally considered more accurate for most people and is recommended by the American Dietetic Association. It was developed in 1990 using modern population data, whereas the Harris-Benedict equation dates back to 1919 (revised in 1984). Studies show the Mifflin-St Jeor formula predicts BMR within 10% of measured values for about 82% of people, compared to about 76% for Harris-Benedict. However, both formulas provide useful estimates. We display both results so you can see the range and use the average if you prefer a middle-ground approach.

How can I use my BMR to lose weight?

To lose weight, you need to create a calorie deficit by eating fewer calories than your TDEE (not your BMR). A safe deficit is 500 calories per day, which leads to approximately 1 pound of weight loss per week since one pound of body fat equals about 3,500 calories. For example, if your TDEE is 2,400 calories, eating 1,900 calories daily should produce steady weight loss. Never eat below your BMR for extended periods, as this can slow your metabolism, cause muscle loss, and lead to nutrient deficiencies. Always consult a healthcare provider before starting any significant calorie restriction program.

Why does BMR decrease with age?

BMR decreases with age primarily because of the gradual loss of lean muscle mass, a process called sarcopenia. Starting around age 30, adults lose approximately 3-8% of muscle mass per decade if they do not engage in regular strength training. Since muscle tissue is more metabolically active than fat tissue (burning about 6 calories per pound at rest versus 2 calories per pound for fat), less muscle means fewer calories burned at rest. Hormonal changes also play a role. Levels of growth hormone and testosterone decline with age, further reducing muscle mass and metabolic rate. Regular resistance training and adequate protein intake can help slow this decline.

How accurate is a BMR calculator and what factors can affect results?

BMR calculators using the Mifflin-St Jeor equation are accurate within about 10% for most healthy adults. However, several factors can cause your actual BMR to differ from the calculated estimate. Body composition is a major factor: two people of the same weight can have very different BMRs if one has more muscle mass. Genetics, thyroid function, certain medications, and hormonal conditions also influence metabolism. Environmental factors like temperature, stress levels, and sleep quality can temporarily affect BMR. For the most precise measurement, consider indirect calorimetry testing at a medical facility. Use calculator results as a practical starting point and adjust based on real-world results over 2-4 weeks.