BMR calculator

BMR (Basal Metabolic Rate) is the energy your body spends at complete rest — breathing, circulating blood, keeping your organs running and your body temperature steady. It's the single largest piece of your daily calorie burn, typically 60–70% of the total.

This tool estimates BMR with the Mifflin–St Jeor equation, the most accurate of the common predictive formulas for the general population:

BMR_male   = 10·W + 6.25·H - 5·A + 5
BMR_female = 10·W + 6.25·H - 5·A - 161
W = body weight (kg), H = height (cm), A = age (years)

Worked example. A 30-year-old man, 178 cm tall, weighing 81.6 kg (180 lb):

BMR = 10·81.6 + 6.25·178 - 5·30 + 5
    = 816 + 1112.5 - 150 + 5
    = 1783.5 ≈ 1784 kcal / day

That's roughly what he would burn lying still for 24 hours. Multiply it by an activity factor and you get TDEE — total daily energy expenditure — the number you actually eat to. Sex matters here because, on average, men carry more lean mass than women at the same height and weight, which is why the male and female constants differ by 166 kcal.

What it isn't. The Mifflin–St Jeor equation is a population estimate built from height, weight, age, and sex — it doesn't know your body composition. Two people with identical stats but very different muscle mass can have BMRs that differ by a few hundred calories. Treat the number as a well-grounded starting point and adjust against real-world results, not a precise measurement.

Common questions

What is BMR? Basal metabolic rate is the number of calories your body uses at complete rest over a day to run its basic functions. It's measured in a fasted, fully rested state and is the baseline for any calorie target.

BMR vs TDEE — what's the difference? BMR is rest-only. TDEE (total daily energy expenditure) is BMR scaled up by an activity multiplier to include walking, training, fidgeting, and digesting food. BMR is the floor; TDEE is what you eat to. Use the TDEE calculator to apply the activity step.

How accurate is Mifflin–St Jeor? Among the common predictive formulas it's the most accurate for the general population, usually landing within about 10% of a measured value. Because it ignores body composition, lean and muscular individuals tend to sit at the higher end of that range. Track your weight over a couple of weeks and adjust your intake if reality disagrees with the estimate.