Free Online Calculators
Resting calorie needs โ Mifflin-St Jeor & Harris-Benedict
This calculator finds your Basal Metabolic Rate (BMR) โ the number of calories your body burns at complete rest just to keep vital functions running. It applies both the Mifflin-St Jeor and Harris-Benedict formulas, using your weight, height, age, and sex. The result gives you a reliable baseline for planning your daily calorie intake.
Your Basal Metabolic Rate (BMR) is the number of calories your body burns simply to stay alive โ breathing, circulating blood, regulating temperature, and keeping every cell functioning while you're completely at rest. Think of it as the minimum energy bill your body pays every single day, whether you exercise or not. Knowing your BMR is the essential first step toward any meaningful nutrition goal, whether you want to lose weight, gain muscle, or simply maintain a healthy lifestyle. Our free BMR Calculator uses both the industry-standard Mifflin-St Jeor equation and the classic Harris-Benedict formula so you can see how both methods compare and make smarter decisions about your calorie intake.
Most people focus on calories burned during exercise, but the truth is that your BMR typically accounts for 60โ75% of your total daily energy expenditure. Even on a completely sedentary day, your body demands a significant number of calories just to survive. If you eat below your BMR for extended periods, your body can respond by slowing your metabolism, breaking down muscle tissue, and storing more fat โ the opposite of what most people want. Understanding your BMR gives you a scientifically grounded baseline, so your diet and fitness plan works with your biology, not against it.
Developed in 1990, the Mifflin-St Jeor equation is widely regarded as the most accurate formula for estimating BMR in the general population. Research has consistently shown it outperforms older methods, which is why our calculator uses it as the primary result.
The only difference between the two is the final constant: +5 for men and โ161 for women, which accounts for the physiological differences in body composition between biological sexes.
The Harris-Benedict equation was first published in 1919 and revised in 1984. While it's older and slightly less accurate on average, it remains widely used and serves as a useful comparison point. The revised (1984) version looks like this:
By showing you both results side by side, our calculator lets you see the range of estimates and choose the value that best fits your planning needs. For most people, the two formulas produce results within 50โ100 calories of each other.
Sarah is 30 years old, weighs 65 kg, and stands 165 cm tall. Using the Mifflin-St Jeor formula: BMR = (10 ร 65) + (6.25 ร 165) โ (5 ร 30) โ 161 = 650 + 1031.25 โ 150 โ 161 = 1,370 calories per day. This means Sarah's body needs at least 1,370 calories just to function at rest. To find her actual daily calorie needs, she would multiply this by an activity factor โ for example, 1.55 for moderate exercise, giving her roughly 2,120 calories to maintain her current weight.
James is 45 years old, weighs 80 kg, and is 180 cm tall. His Mifflin-St Jeor BMR = (10 ร 80) + (6.25 ร 180) โ (5 ร 45) + 5 = 800 + 1125 โ 225 + 5 = 1,705 calories per day. Since James trains heavily โ running 50+ km per week โ he applies an activity multiplier of 1.725, pushing his total daily energy expenditure to approximately 2,940 calories. Without knowing his BMR first, James might drastically undereat, risking injury and poor recovery.
Linda is 55, weighs 72 kg, and is 162 cm tall. Her BMR = (10 ร 72) + (6.25 ร 162) โ (5 ร 55) โ 161 = 720 + 1012.5 โ 275 โ 161 = 1,296.5 calories per day. Linda notices her BMR is noticeably lower than it was at 35, which explains why her previous diet plan no longer works as well. Armed with this number, she adjusts her calorie target and macronutrient balance more precisely, rather than simply eating less and feeling frustrated.
Your BMR is your resting baseline โ it doesn't account for any physical activity. To estimate your Total Daily Energy Expenditure (TDEE), multiply your BMR by one of the standard activity factors below:
To lose weight, aim for a calorie intake roughly 500 calories below your TDEE. To gain muscle, add 250โ500 calories above your TDEE. Always ensure you eat at or above your BMR to protect metabolic health.
The Mifflin-St Jeor equation has been validated in numerous studies and is accurate within approximately 10% for most adults. Factors like unusually high muscle mass, certain medical conditions, or hormonal imbalances can cause individual variation. For clinical or medical decisions, always consult a registered dietitian or physician who can assess your specific circumstances more precisely.
Yes โ BMR is not fixed. It tends to decrease gradually with age, partly because muscle mass naturally declines (a process called sarcopenia) and partly due to hormonal changes. Significant weight loss can also lower your BMR, which is why many people hit plateaus on calorie-restricted diets. Strength training is one of the most effective ways to preserve or increase muscle mass and keep your BMR higher as you age.
No. Your BMR represents the calories needed for zero activity โ even lying still all day burns slightly more than your pure BMR. Consistently eating only at your BMR level, especially if you're active, can lead to nutrient deficiencies, fatigue, and muscle loss. Always use your TDEE (BMR multiplied by your activity level) as your true maintenance calorie target, and adjust from there based on your goals.