BMR Calculator

Your Basal Metabolic Rate (BMR) is the number of calories your body burns at complete rest, just to stay alive — running your heart, lungs, brain, and the constant repair of your cells. It is the single biggest part of your daily calorie burn, usually 60–70% of the total. Get this number right and everything downstream — maintenance calories, a diet, a bulk — has a solid base.

How BMR is calculated

To calculate BMR, this calculator uses the Mifflin-St Jeor equation, which research has found to be the most accurate for most people:

• Men: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age + 5
• Women: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age − 161

The two formulas are identical except for the last number, which accounts for the difference in average body composition between the sexes. A worked example each way: a 30-year-old man who is 180 cm (5 ft 11 in) and 80 kg (176 lb) has a BMR of about 1,780 kcal/day, while a 30-year-old woman at 165 cm (5 ft 5 in) and 65 kg (143 lb) comes out at about 1,370 kcal/day — in both cases, the energy they would burn doing nothing at all. You can enter your own details in metric or imperial — the calculator converts automatically before applying the formula.

Mifflin-St Jeor vs Harris-Benedict

You will see more than one equation quoted for BMR. This calculator uses Mifflin-St Jeor (published 1990), which studies have repeatedly found to predict resting energy expenditure most accurately across the general population. The older Harris-Benedict equation (1919, revised 1984) tends to read a little high, particularly for people carrying more body fat. A third option, Katch-McArdle, works from your lean body mass rather than total weight, so it can be more precise — but only if you already know your body-fat percentage. For most people, without a body-fat reading, Mifflin-St Jeor is the sensible default, which is why it is the one here.

From BMR to daily calories

You never actually burn just your BMR, because you move. Multiplying BMR by an activity factor gives your total daily calorie needs — shown in the table beside the calculator for each activity level, from sedentary to very active. That total is your TDEE, the number to eat around to maintain your weight. The TDEE calculator walks through that second step, and the calorie calculator turns it into loss or gain targets.

What affects your BMR

BMR rises with more muscle mass and greater body size, and it drifts down gradually with age as muscle is lost. Sex plays in too: men usually have a higher BMR than women of the same size because they carry more muscle, which is why the women’s formula ends in −161. One thing worth knowing — crash dieting can lower your BMR temporarily, as the body adapts to a sharp shortage of food. That is why very steep diets so often stall. Because BMR is an estimate, use it as a baseline and adjust based on how your weight actually behaves over time.