Calculate your Basal Metabolic Rate using both the Mifflin-St Jeor and Harris-Benedict equations.
BMR Results
About the BMR Calculator — Basal Metabolic Rate Calculator
The BMR calculator estimates how many calories your body burns each day at complete rest — simply to keep vital systems running. Your basal metabolic rate accounts for breathing, circulation, temperature regulation, hormone production, and cell repair. Knowing your BMR is the essential first step in planning any weight loss, weight gain, or maintenance nutrition strategy, because every calorie target ultimately starts from this baseline number.
This basal metabolic rate calculator supports both the Mifflin-St Jeor equation and the Harris-Benedict equation, displaying both results side by side so you can compare them. It accepts metric inputs (kg, cm) and imperial inputs (lbs, feet, inches) and is suitable for adults of any age and either gender. Fitness enthusiasts use it to calibrate their macros, dietitians use it with clients to set realistic deficits, and personal trainers reference it when designing cutting or bulking programmes.
How to Use the BMR Calculator
Select your unit system — Choose Imperial (pounds, feet, inches) or Metric (kilograms, centimetres) depending on what measurements you have available.
Enter your age — Age significantly affects BMR because metabolic rate typically decreases by roughly 1–2% per decade after age 20.
Select your gender — Men and women have different muscle-to-fat ratios on average, so the formulas use separate constants for each.
Enter your height and weight — Use your current weight, not your goal weight. BMR reflects your body as it is now.
Click Calculate BMR — Results from both formulas appear instantly, showing calories per day at rest for comparison.
The Two Formulas Explained
The Mifflin-St Jeor equation, developed in 1990, is considered the most accurate predictor of resting metabolic rate for most people. It uses weight in kilograms, height in centimetres, and age in years: for men, BMR = 10W + 6.25H − 5A + 5; for women, BMR = 10W + 6.25H − 5A − 161. Research published in the Journal of the American Dietetic Association (2005) found it consistently outperforms older formulas across a wide range of body types and weights.
The Harris-Benedict equation, originally published in 1919 and revised in 1984, was the gold standard for decades. The revised version gives: for men, BMR = 88.362 + 13.397W + 4.799H − 5.677A; for women, BMR = 447.593 + 9.247W + 3.098H − 4.330A. It tends to produce slightly higher estimates than Mifflin-St Jeor, particularly for individuals who are overweight, which is why the newer formula is now preferred in clinical practice.
Tips for Getting the Best Results
Use your current weight, not your goal weight: BMR is a snapshot of your current metabolism. Using your target weight would underestimate your actual daily calorie needs and could lead you to eat too little, triggering metabolic adaptation and muscle loss.
Multiply by an activity factor to get TDEE: Your BMR alone does not account for movement. Multiply it by 1.2 (sedentary), 1.375 (light activity), 1.55 (moderate exercise), 1.725 (very active), or 1.9 (extremely active) to estimate your Total Daily Energy Expenditure, which is the number most people actually need for diet planning.
Re-calculate as your weight changes: BMR changes as your body composition changes. If you lose or gain more than 5kg, recalculate to ensure your calorie targets remain accurate. A BMR calculated at 90kg will overestimate needs once you reach 75kg.
Use Mifflin-St Jeor as your primary reference: Both formulas are shown for comparison, but the Mifflin-St Jeor result is the more accurate of the two for the majority of adults. If they differ significantly, prefer the Mifflin-St Jeor value for setting calorie targets.
Consider lean mass for more precision: Both equations estimate BMR from total body weight, which does not distinguish muscle from fat. If you have a very high or very low body fat percentage, consider using a Katch-McArdle formula (not shown here) that uses lean body mass for a more individualised estimate.
Why Use a BMR Calculator Online
Manual BMR calculations involve multi-step formulas with different constants for each gender and formula, making errors common. This basal metabolic rate calculator does the arithmetic instantly and correctly every time. It runs entirely in your browser — no data is sent to a server, no account is needed, and results appear immediately. Metric and imperial units are both supported, so there is no need to convert your measurements before entering them.
The side-by-side display of both formulas gives fitness enthusiasts, dietitians, and trainers the full picture. Students studying nutrition science can verify their manual calculations. Anyone tracking a weight-loss journey can check their BMR periodically as their weight changes. The clean interface works on mobile, tablet, and desktop without any app to install.
Frequently Asked Questions about BMR Calculator
The Mifflin-St Jeor equation is considered more accurate for most people. A large 2005 study found it had the smallest mean difference from directly measured resting metabolic rate across a diverse population. The Harris-Benedict equation was the standard for decades but tends to overestimate BMR in overweight individuals by 5% or more, making it less reliable for people with higher body fat percentages.
BMR is the calories your body burns at absolute rest — no movement, no digestion, no activity. TDEE (Total Daily Energy Expenditure) is your actual daily calorie burn, which includes BMR plus all physical activity. TDEE is calculated by multiplying BMR by an activity multiplier ranging from 1.2 for sedentary people up to 1.9 for those with very physically demanding lifestyles or intense daily training.
Eating significantly below BMR for extended periods is generally not recommended. Your BMR represents the minimum calories needed for vital organ function. Consistently eating below this level can lead to muscle tissue breakdown, nutrient deficiencies, hormonal disruption, and metabolic adaptation where your body reduces its calorie burn to compensate. Most nutrition professionals recommend a deficit no greater than 500–750 calories below TDEE, not below BMR.
The Mifflin-St Jeor and Harris-Benedict equations use different mathematical constants derived from different research populations and time periods. Harris-Benedict was developed in 1919 (revised 1984) using a smaller, less diverse sample. Mifflin-St Jeor was published in 1990 with a broader population. The difference is typically 50–150 calories per day, and is larger for people who are overweight where Harris-Benedict tends to produce higher estimates.
Yes. BMR naturally decreases as you age, primarily because lean muscle mass tends to decline with age — a process called sarcopenia. Both the Mifflin-St Jeor and Harris-Benedict formulas subtract a value proportional to age, reflecting this trend. On average, BMR decreases by roughly 1–2% per decade after age 20. Regular strength training can partially offset this decline by preserving or increasing lean muscle mass.
Standard BMR formulas are less accurate for athletes with unusually high muscle mass, since muscle tissue burns more calories than fat at rest. Both Mifflin-St Jeor and Harris-Benedict use total body weight, not lean mass. Athletes with very low body fat and high muscle mass may find that lean-mass-based formulas like Katch-McArdle produce more accurate estimates. As a practical rule, athletes should treat the calculator result as a minimum baseline and adjust upward based on actual performance and body composition changes.
No. BMR is strictly the energy used at complete metabolic rest — no food digestion, no movement, no activity. Digesting food requires additional energy, a process called the thermic effect of food (TEF), which accounts for roughly 10% of total daily calorie expenditure. TEF is included in TDEE calculations but not in BMR. This is another reason why eating at BMR level — rather than at TDEE level — creates a larger actual deficit than people expect.
Use your BMR as a starting point, not as your calorie target. First multiply it by your activity factor to estimate TDEE. Then subtract 300–500 calories from TDEE to create a moderate, sustainable deficit. Eating at BMR directly would likely put most people in too large a deficit, especially those who are physically active. For personalised guidance, combine the basal metabolic rate calculator result with advice from a registered dietitian.