BMR Calculator
Enter your age, sex, weight, and height to find your basal metabolic rate, the calories your body burns at complete rest. Choose between the Mifflin-St Jeor, revised Harris-Benedict, or body-fat-based Katch-McArdle formula, switch between metric and imperial units, read the result in kcal or kJ, and see your full daily calorie needs across five activity levels.
Formula
Worked example
A 30-year-old man, 70 kg, 175 cm with Mifflin-St Jeor: 10×70 + 6.25×175 − 5×30 + 5 = 700 + 1093.75 − 150 + 5 ≈ 1,649 kcal/day. A sedentary day (×1.2) is about 1,979 kcal, a very active day (×1.725) about 2,845 kcal.
How the three BMR formulas work
This calculator offers the three formulas used by clinicians and most reputable online tools. Mifflin-St Jeor, developed in 1990 and the formula recommended by the Academy of Nutrition and Dietetics, applies a sex offset of +5 kcal for men and -161 kcal for women on top of weight, height and age terms. The revised Harris-Benedict equation (Roza and Shizgal, 1984) uses different coefficients and tends to read a little higher, which is why Mifflin-St Jeor replaced it as the default. Katch-McArdle ignores sex entirely and works from lean body mass, so it needs your body fat percentage; for lean and athletic people who know their body composition it is often the most accurate of the three. Switch formulas to compare, and read the show-your-work panel to see exactly how your number is built.
From BMR to daily calories
BMR is the energy your body would burn over 24 hours at complete rest, covering only circulation, respiration and thermoregulation. Your real need is higher because movement, digestion and exercise all add calories. To get total daily energy expenditure (TDEE) you multiply BMR by an activity factor from 1.2 for a sedentary day up to 1.9 for very hard training or a physical job. The breakdown table shows that whole scale at once, so you can read maintenance calories straight off the row that matches your week. To lose weight gradually, eat roughly 500 kcal below that figure; to gain, eat above it.
Units, accuracy and limitations
Enter measurements in metric or imperial and read the result in calories or kilojoules; the calculator converts automatically and one kilocalorie equals 4.184 kJ. Equation-based estimates are baselines, not measurements. They were derived mostly from non-obese, non-athletic adults, so accuracy can fall at the extremes of body composition, and they cannot capture hormonal conditions such as hypothyroidism, pregnancy, fever, or the metabolic slowing that follows significant weight loss. For general wellness tracking the figure is a sound starting point, but caloric targets for medical weight management should involve a registered dietitian or physician. This tool is for general information only and is not medical advice.
Activity multipliers (BMR to TDEE)
| Activity level | Typical week | Multiplier |
|---|---|---|
| Sedentary | Little or no exercise, desk job | 1.2 |
| Lightly active | Light exercise 1-3 days/week | 1.375 |
| Moderately active | Moderate exercise 3-5 days/week | 1.55 |
| Very active | Hard exercise 6-7 days/week | 1.725 |
| Extra active | Very hard exercise or physical job | 1.9 |
Multiply your BMR by the factor that best matches a typical week to estimate maintenance calories.
Frequently asked questions
What is a normal BMR for adults?
BMR varies widely with body size, age, and sex, so there is no single 'normal' value. As a rough reference, many adult women fall between 1,200 and 1,600 kcal/day and adult men between 1,500 and 2,000 kcal/day at rest, but individuals outside these ranges are not abnormal. The meaningful number is your personal BMR in context of your actual body measurements.
Is the Mifflin-St Jeor equation more accurate than Harris-Benedict?
Yes, for most adults. A widely cited 2005 review in the Journal of the American Dietetic Association found that the Mifflin-St Jeor equation predicted measured resting energy expenditure within 10% more often than the original Harris-Benedict equation. The Harris-Benedict formula, published in 1919, was derived from a smaller sample and tends to overestimate BMR in overweight individuals. Mifflin-St Jeor is now the preferred equation in clinical nutrition guidelines.
Does BMR change if I lose or gain weight?
Yes, BMR changes with body weight because the equation is directly proportional to mass. Losing weight generally lowers BMR, partly through reduced body mass and partly through adaptive thermogenesis, a metabolic slowing beyond what the equation predicts, which is why recalculating periodically during a weight-loss effort is advisable. Significant changes in muscle mass, such as those from resistance training, can partially offset the weight-loss-related decline in BMR.
Which BMR formula should I choose?
For most people, use Mifflin-St Jeor, the formula clinical nutrition guidelines recommend for the general adult population. Pick Katch-McArdle if you know your body fat percentage and are lean or athletic, since it works from lean body mass and ignores sex. The revised Harris-Benedict equation is offered for comparison and tends to read slightly higher. This calculator lets you switch between all three so you can see the spread.
How do I turn my BMR into the calories I actually need?
Multiply your BMR by an activity factor: 1.2 for a sedentary day, 1.375 lightly active, 1.55 moderately active, 1.725 very active, and 1.9 for extra active. The result is your total daily energy expenditure (TDEE), or maintenance calories. The breakdown table on this page shows all five levels at once. To lose about half a kilogram (one pound) a week, eat roughly 500 kcal below the matching figure.