BMR Calculator

TL;DR: To calculate your Basal Metabolic Rate (BMR), use the Mifflin-St Jeor equation: for men, BMR = (10 × weight in kg) + (6.25 × height in cm) - (5 × age in years) + 5; for women, BMR = (10 × weight in kg) + (6.25 × height in cm) - (5 × age in years) - 161, then multiply the result by 1.2 (sedentary) or 1.55 (moderately active) to estimate your Total Daily Energy Expenditure (TDEE).

What Is the BMR Calculator?

The BMR Calculator estimates your Basal Metabolic Rate—the exact number of calories your body burns at complete rest to maintain vital functions like breathing, circulation, cell production, and nutrient processing. This is not the same as the calories burned through exercise or daily movement. It represents the energy required just to keep you alive if you were to stay in bed for 24 hours. For most adults, this figure accounts for 60 to 75 percent of total daily calorie expenditure, making it the dominant factor in weight management.

This tool is essential for anyone tracking body composition, planning a fat-loss phase, building muscle, or simply trying to understand their metabolic baseline. Athletes, dietitians, and fitness enthusiasts rely on this calculation because it removes guesswork from nutrition planning. Instead of using generic 2,000-calorie guidelines, you get a personalized baseline. The calculator also applies an activity multiplier to estimate your Total Daily Energy Expenditure (TDEE), which represents all calories burned in a day, including physical activity. Understanding this distinction is critical, as confusing BMR with TDEE is the most frequent error in calorie planning.

The calculator is built on the Mifflin-St Jeor equation, which was published in 1990 and is recognized by the Academy of Nutrition and Dietetics as the most accurate predictive formula for the general population. This replaced older equations like the original Harris-Benedict formula, which often overestimates requirements by 5 to 10 percent. With inputs of weight, height, and age, you can obtain a scientifically validated estimate in seconds.

How to Use the Calculator

1. Enter Weight: Input your current body weight in kilograms (kg). If you know your weight in pounds, divide that number by 2.2046 to convert to kg before entering it. Ensure this is your current weight, not your goal weight.
2. Enter Height: Input your height in centimeters (cm). If you measure in feet and inches, convert to centimeters by multiplying total inches by 2.54. For example, 5'10" equals 70 inches, which converts to 177.8 cm.
3. Enter Age: Input your age in years. Use your exact chronological age. The formula accounts for age because metabolic rate naturally declines with age due to loss of lean muscle mass. Do not round down or use "biological age" estimates.
4. Select Gender: Choose male or female. The equation includes a gender adjustment because men generally have a higher percentage of lean muscle mass and lower body fat percentage, which increases BMR. Women receive a base deduction of 166 calories compared to men with identical measurements.
5. Select Activity Level: Choose between Sedentary (1.2) or Active (1.55). Sedentary describes little to no exercise—mostly sitting during work and leisure, such as desk jobs. Active describes moderate exercise 3 to 5 days a week or a job involving physical labor. This multiplier converts your BMR into your TDEE.
6. Click Calculate: Press the calculate button. The result will display your BMR in calories per day. The calculator will also display your estimated TDEE based on your chosen activity multiplier.
7. Compare Genders: Review the comparison output. For the same height, weight, and age, a female will often see a BMR 100–170 calories lower than a male due to the formula's sex-specific constant. This insight helps set realistic expectations for calorie targets.

Formula and Calculation Method

The calculator uses the Mifflin-St Jeor equation, which is the most validated predictive formula for resting energy expenditure. The equation differs slightly for men and women due to differences in body composition and hormonal influences on metabolism. The formula is:

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

After calculating BMR, the tool applies your selected activity multiplier to estimate TDEE: Sedentary (1.2) or Active (1.55). This multiplication accounts for the additional energy expended through daily movement and structured exercise. The final TDEE is your maintenance calorie level—eating this amount should keep your weight stable.

Worked Example: Consider a 30-year-old male weighing 75 kg and measuring 175 cm tall. Plug these numbers into the male equation:

BMR = (10 × 75) + (6.25 × 175) - (5 × 30) + 5
BMR = 750 + 1093.75 - 150 + 5
BMR = 1698.75 calories per day

If this man is sedentary, his TDEE is 1698.75 × 1.2 = 2038.5 calories. If he is active, his TDEE becomes 1698.75 × 1.55 = 2633.06 calories. This means his BMR alone—before any exercise or daily movement—accounts for about 1,700 calories. If he wants to lose weight, he would target roughly 500 calories below his TDEE, creating the widely accepted deficit for about 0.5 kg of fat loss per week. Critically, he must recalculate when his weight changes by 5 kg, as the BMR will drop alongside weight loss.

Practical Examples

To understand how this calculator applies to different individuals, review the following real-world scenarios. These illustrate how small input changes affect output and how BMR compares to TDEE.

In the first scenario, the 40-year-old male has a BMR of 1725 calories. If he is sedentary, his total daily burn is only 2070 calories. Many people overestimate this number, assuming they burn more due to "thinking" or "breathing." In reality, if he eats 2,500 calories daily, he accumulates a surplus of 430 calories per day, translating to roughly 0.5 kg of fat gain weekly. The second scenario highlights a gender difference: the 25-year-old female has a BMR nearly 360 calories below the male in scenario one despite being younger and lighter—this is normal and driven by lean mass differences. The third scenario shows the age penalty: the 68-year-old has a BMR 250 calories lower than the 40-year-old male with identical weight and similar height. This is why dietary needs shrink with age.

Tips for Accurate Results

• Recalculate after 5 kg weight changes: BMR scales directly with body mass. If you lose 5 kg, your BMR decreases by roughly 50 calories per day (10 × 5 kg). Failing to recalculate leads to plateaus because your maintenance calories have dropped.
• Never confuse BMR with TDEE: BMR is the absolute resting rate. TDEE includes your activity multiplier. If you use BMR as your calorie target, you will be in a severe deficit, which can cause muscle loss and hormonal disruption. Always use TDEE for maintenance or deficit planning.
• Use metric units correctly: The formula requires kilograms and centimeters. Pounds must be divided by 2.2046; feet and inches must be converted via total inches multiplied by 2.54. A single unit error can skew results by 100–200 calories.
• Avoid the obsolete Harris-Benedict formula: Many older websites still use the 1919 original equation. That formula overestimates BMR by up to 10% because it was derived from a smaller, less diverse population. The Mifflin-St Jeor equation in this calculator is the current clinical standard.
• Be honest with activity levels: Most people overestimate their activity. If you have a desk job and exercise once a week, you are sedentary (1.2), not active (1.55). Choosing active while sedentary will lead to overeating and weight gain.
• Account for age precisely: Entering an incorrect age by even 5 years shifts the BMR by 25 calories. For long-term tracking, update your age annually on your birthday.
• Use this as a baseline, not a law: Individual metabolic variations occur due to thyroid function, genetics, and medications. The calculated numbers are highly accurate for populations but may differ slightly for individuals. Monitor weight trends for 2–3 weeks and adjust intake by 100–150 calories as needed.

Frequently Asked Questions

1. Is the BMR the same as the number of calories I need to eat to lose weight?
No. BMR is the calories burned at complete rest. To lose weight, you need to know your Total Daily Energy Expenditure (TDEE), which is calculated by multiplying your BMR by your activity factor (1.2 or 1.55 in this calculator). To lose approximately 0.5 kg per week, subtract 500 calories from your TDEE, not your BMR. For example, if your BMR is 1700 and you are sedentary, your TDEE is 2040 calories. A weight-loss target would be around 1540 calories daily. Eating exactly at your BMR of 1700 would create a deficit of only 340 calories, leading to slower loss than intended.

2. Why does the female formula subtract 161 while the male formula adds 5?
The difference in the constants reflects average physiological differences between sexes. Men typically have a higher proportion of lean muscle mass and lower essential fat stores, which increases resting metabolic rate. The plus 5 for men and minus 161 for women means that, for identical weight, height, and age, a woman's BMR will be exactly 166 calories lower than a man's. This is not a flaw in the formula; it is an empirically derived adjustment based on thousands of metabolic measurements. For example, a 30-year-old male and female both at 70 kg and 170 cm will have BMRs of approximately 1670 and 1504 calories, respectively.

3. How often should I recalculate my BMR, and does it change as I lose weight?
You should recalculate your BMR every time your body weight changes by 5 kg (approximately 11 pounds). Because the formula uses weight as a core variable, losing 5 kg will lower your BMR by about 50 calories per day (10 calories per kg). If you lose 10 kg total, your BMR drops by roughly 100 calories. This means your maintenance calories also decrease. If you do not adjust your intake after significant weight loss, your deficit shrinks, and weight loss stalls. Additionally, BMR decreases with age (about 5 calories per year after age 20), so recalculating annually or after major body composition changes is advised for accurate calorie targets.