Estimate your basal metabolic rate (BMR) — the number of calories your body burns at complete rest — using the Harris-Benedict equation. Enter your sex, age, height, and weight, and the calculator returns your BMR plus your total daily energy expenditure (TDEE) across six activity levels, so you know roughly how many calories you need each day.
The Harris-Benedict calculator estimates your basal metabolic rate (BMR) — the amount of energy, measured in calories, that your body needs to keep functioning while at complete rest. Even when you are lying perfectly still, your body is hard at work: your heart beats, your lungs breathe, your brain fires, your kidneys filter, and every cell maintains itself. All of that requires energy, and BMR is the number that captures it. For most people, BMR accounts for around 60 to 70 percent of the total calories they burn in a day, which is why it is the essential starting point for any calorie plan, whether your goal is to lose weight, gain muscle, or simply maintain your current physique.
The Harris-Benedict equation is one of the oldest and most widely used formulas for estimating BMR. First published in 1919 and revised in 1984, it uses four simple inputs — your sex, age, height, and weight — to produce a personalized estimate. This calculator applies the revised Harris-Benedict equation and then multiplies your BMR by a set of activity factors to give you your total daily energy expenditure (TDEE), the number that tells you how many calories you actually burn on a typical day once movement and exercise are included.
Your basal metabolic rate is the minimum number of calories your body needs to sustain its most basic, life-preserving functions over 24 hours. These functions run automatically and continuously, whether you are awake or asleep, and include:
BMR is measured under strict conditions: after a full night's sleep, in a fasted state, at a comfortable temperature, and while completely at rest. Because these conditions are hard to reproduce outside a laboratory, a closely related term — resting metabolic rate (RMR) — is often used interchangeably. RMR is measured under slightly less restrictive conditions and tends to be a few percent higher, but for everyday planning the two are treated as roughly equivalent.
This calculator uses the revised Harris-Benedict equations, which improved the accuracy of the original 1919 formulas. The equations differ by sex, because men and women have different average body compositions, with men typically carrying more lean muscle mass, which is metabolically active tissue. The formulas are:
Men: BMR = 66.5 + (13.75 × weight in kg) + (5.003 × height in cm) − (6.75 × age)
Women: BMR = 655.1 + (9.563 × weight in kg) + (1.850 × height in cm) − (4.676 × age)
Each term reflects a real physiological relationship. Weight has the largest coefficient because a bigger body has more tissue to maintain and therefore burns more energy at rest. Height adds a smaller contribution, since taller people generally have larger organs and greater surface area. Age is subtracted, because metabolism gradually slows as we get older — largely due to the natural loss of muscle mass over the decades. The constant at the front (66.5 for men, 655.1 for women) anchors the equation so that the result lands in a realistic range.
Suppose a 25-year-old man who is 180 cm tall and weighs 75 kg wants to know his BMR. Plugging the numbers into the men's equation:
So his BMR is about 1,830 calories per day. That is the energy his body would burn if he did nothing but rest for 24 hours. To find out how many calories he needs on a normal day, we multiply this figure by an activity factor, as explained below. These are the default values in the calculator, so you can press Calculate to see the full breakdown and then swap in your own numbers.
Your BMR only tells part of the story, because almost nobody spends all day lying down. Every time you stand, walk, work, exercise, or even fidget, you burn additional calories on top of your basal rate. To capture this, the Harris-Benedict method multiplies your BMR by an activity factor (also called the physical activity level, or PAL). The result is your total daily energy expenditure (TDEE) — the number of calories you burn in a full, typical day.
This calculator uses six activity levels:
For our example man with a BMR of 1,830 calories, a moderately active lifestyle (×1.55) puts his TDEE at about 2,836 calories per day. That is roughly how much he needs to eat to maintain his current weight given that activity level. Choosing the level that honestly matches your week is important: overestimating your activity is one of the most common reasons a calorie plan stalls.
All calculations are performed in metric units internally; if you enter inches or pounds, the calculator converts them for you, so you always get an accurate result no matter which units you prefer.
Many factors influence how many calories your body burns at rest. The Harris-Benedict equation captures the four largest and most measurable ones — sex, age, height, and weight — but it is worth understanding the full picture:
Once you know your TDEE, you have a practical target for managing your weight, because weight change comes down to the balance between calories consumed and calories burned:
A widely cited rule of thumb holds that a deficit or surplus of about 3,500 calories corresponds to roughly one pound of body weight. While the human body is more complex than that simple figure suggests — metabolism adapts, appetite shifts, and water weight fluctuates — it remains a useful mental model for setting realistic expectations. Whatever your goal, it is generally wise not to drop below about 1,200 calories per day for women or 1,500 for men without medical supervision, since very low intakes make it hard to get adequate nutrition and can slow your metabolism further.
The Harris-Benedict equation is not the only way to estimate BMR. Two other formulas are commonly used, and it helps to understand how they compare:
The Harris-Benedict equation remains popular because it is reliable, well studied, and requires only information most people already know. For the general population it produces estimates close to those of Mifflin-St Jeor, usually within a few percent. If you are very lean and know your body fat percentage, Katch-McArdle may serve you better; otherwise, Harris-Benedict is an excellent and time-tested choice.
Like all predictive equations, Harris-Benedict gives an estimate, not a laboratory measurement. Studies have found it accurate to within about 10 to 15 percent for most people, which is more than good enough for setting a starting calorie target. Its main limitation is that it cannot account for individual differences in body composition: because it uses total weight rather than lean mass, it may overestimate the BMR of people with a high body fat percentage and underestimate it for very muscular individuals. It was also developed decades ago on populations that differ from today's, which is part of why the revised version and newer equations exist.
The best way to use any BMR estimate is as a starting point. Calculate your TDEE, eat at that level for two or three weeks, and track your weight. If the scale is not moving the way you expect, adjust your intake up or down by 100 to 200 calories and observe again. Your real-world results are the ultimate feedback, and they let you fine-tune a formula-based estimate into a plan that genuinely fits your body.
More than a century after it was first published, the Harris-Benedict equation endures because it strikes an ideal balance between simplicity and usefulness. It asks only for facts you already know, it produces a personalized number rather than a generic guess, and it forms the foundation of the calorie targets used by countless fitness apps, nutrition programs, and health professionals. Understanding where that number comes from — and what it does and does not capture — puts you in control of your own nutrition. Whether you are planning a cut, a bulk, or steady maintenance, knowing your BMR and TDEE turns vague guesswork into a clear, actionable plan.
BMR is the calories your body burns at complete rest to stay alive. TDEE is your total daily calorie burn, which is your BMR multiplied by an activity factor to account for movement and exercise. TDEE is always higher than BMR.
For the general population, Mifflin-St Jeor is often considered slightly more accurate, but the two produce very similar results for most people. Harris-Benedict remains a trusted, widely used equation, and both are excellent starting points.
No — you should not eat only your BMR. Base your calorie target on your TDEE, then subtract a moderate deficit (such as 500 calories) to lose weight. Eating at or below BMR for long periods is usually too aggressive and hard to sustain.
Metabolism slows with age mainly because we tend to lose muscle mass over time, and muscle burns more calories than fat. Staying physically active and doing resistance training can help preserve muscle and keep your BMR higher.
Yes. You can enter your weight in kilograms or pounds and your height in centimeters or inches. The calculator converts everything to metric internally before applying the Harris-Benedict equation, so the result is accurate either way.
Recalculate whenever your weight changes noticeably — for example, every 5 to 10 pounds — since weight is a major input. It is also worth updating as you age. Keeping the number current ensures your calorie targets stay realistic.
This Harris-Benedict Calculator is provided for general informational and educational purposes only. It gives an estimate of basal metabolic rate and daily calorie needs based on a predictive equation and is not a substitute for professional medical or nutritional advice. Individual energy requirements vary with body composition, health conditions, and other factors. Consult a qualified healthcare provider or registered dietitian before making significant changes to your diet, especially if you have a medical condition.