BMR Calculator

Find out how many calories your body burns at rest, then see rough daily targets for your activity level.

📖 How it works & FAQ

Sex

Age (years)

Units

Weight (kg)

Height (cm)

0 BMR (calories/day) Mifflin-St Jeor, at complete rest

0 Sedentary Little or no exercise (x1.2)

0 Moderately active Exercise 3-5 days/week (x1.55)

0 Very active Hard exercise 6-7 days/week (x1.725)

What BMR actually measures

Your Basal Metabolic Rate (BMR) is the number of calories your body would burn in 24 hours if you did nothing but rest, breathe, and keep your organs running. It is the single biggest slice of your daily energy use, usually 60-70% of the total, before any walking, working, or exercise is added on top.

The Mifflin-St Jeor equation

This calculator uses the Mifflin-St Jeor formula, which most dietitians consider the most accurate general estimate. For men it is 10 × weight(kg) + 6.25 × height(cm) - 5 × age + 5. For women the final constant changes to -161. Imperial entries are converted to kilograms and centimetres before the math runs, so both unit modes give the same result.

Turning BMR into daily calories

To estimate the calories you actually need in a day, BMR is multiplied by an activity factor. This calculator shows sedentary (×1.2), moderately active (×1.55), and very active (×1.725) so you can pick the row that matches your week. Eating around your maintenance number holds weight steady; a modest deficit trends down, a surplus trends up.

How to use it

Choose your sex and enter your age in years.
Pick metric or imperial units.
Type your weight and height in the matching boxes.
Read your BMR and the activity-adjusted daily calorie estimates, which update as you type.

These numbers are estimates for general education, not medical or nutritional advice. Talk to a doctor or registered dietitian before making big changes.

FAQ

Is BMR the same as the calories I should eat?: No. BMR is your at-rest burn. Your daily need is higher because it includes movement, which is what the activity multipliers estimate.
Why does the formula treat men and women differently?: On average, body composition differs, so the equation uses a +5 constant for men and -161 for women to reflect typical differences in lean mass.
Which activity level should I pick?: Be honest about a normal week. Most people with a desk job and a few workouts land between sedentary and moderately active.
How accurate is this?: It is a solid population estimate but individual metabolism varies. Track your weight for two to three weeks and adjust from what you actually see.