BMR Calculator

This page uses the Mifflin-St Jeor equation, the prediction most clinical dietitians reach for today because it tracked measured resting energy expenditure more closely than the older Harris-Benedict formula it replaced. For men: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age + 5. For women: the same three terms, but − 161 instead of + 5. A 30-year-old man at 70 kg and 170 cm gets 700 + 1062.5 − 150 + 5 ≈ 1,618 kcal/day. Enter pounds and inches if you prefer — the toggle changes only the display, and the equation still runs in kilograms and centimeters. The sex term is a fixed offset, not a biological claim about any individual. It is there because, averaged across the population the equation was fitted to, men carried more lean mass at the same height and weight — and lean mass is what burns energy at rest.

BMR is the energy your body spends doing nothing at all: keeping a heart beating, lungs moving, kidneys filtering, a brain running, a body at temperature. It is the floor of daily energy use, and for a sedentary person it is usually the largest single share of the day. What drives it is mostly fat-free mass — organs and muscle rather than fat tissue. That is why two people at the same weight can have genuinely different resting burn, and why the figure tends to drift down with age as lean tissue is lost. Strictly, "basal" means measured after an overnight fast, at rest, at a comfortable temperature. What predictive equations estimate is closer to resting metabolic rate, a slightly higher figure taken under less severe conditions. In everyday use the two terms are treated as interchangeable, and the difference is small next to the error in the prediction itself.

Almost nobody spends the day lying still, so this number is not something to eat against. Multiplying it by an activity factor — 1.2 for sedentary up to 1.9 for very heavy training — gives total daily energy expenditure, which is what the table above lays out. Those factors are broad brackets meant to cover a whole week, not a good day. Three gym sessions around a desk job is light to moderate, not intense, and picking one bracket too high is the most common way this calculation goes wrong. Eating at BMR while living an ordinary day therefore means an unintended and often steep deficit. That is one reason a figure produced by a calculator is not a plan.

The equation is a regression fitted to a population, and individuals scatter around the line it draws. Body composition is the biggest single reason: at the same height, weight, age and sex, more lean mass means a higher resting burn than the formula predicts, and less means a lower one. Thyroid function, some medications, illness, fever, a recent large weight change and genetics all move the real figure too, and none of them appear in the four input fields. The only way to know your resting expenditure rather than estimate it is to measure it, with indirect calorimetry — a clinical test that a web page does not substitute for. So treat the output as an informed starting estimate, and if you are using it to plan anything, let the trend in your weight over several weeks be the signal that matters.

Prediction equations of this kind were fitted on healthy adults and carry no authority outside that group. Children and teenagers have energy needs tied to growth and are assessed differently. Pregnancy and breastfeeding add requirements this formula does not model. Anyone acutely ill, recovering from surgery, living with a thyroid or metabolic condition, or taking medication that affects metabolism needs a clinical estimate rather than a web form. If you have any history of disordered eating, a calorie number from a calculator is a poor thing to anchor on, and a clinician is the right person to talk to instead. This page explains what the equation computes and where it fails. It does not tell you how many calories to eat — decisions about intake, weight and training belong with a physician or a registered dietitian who knows your history.