Harris-Benedict BMR Calculator

The Harris-Benedict equation estimates your Basal Metabolic Rate (BMR), the number of calories your body burns at complete rest just to keep you alive. Heart beating, lungs breathing, liver processing: all of that has an energy cost, even in bed.

Two different equations get confused here, so to be precise about the dates: Harris and Benedict published the original in 1918, Roza and Shizgal revised it in 1984, and the rival Mifflin-St Jeor equation came later, in 1990. Mifflin-St Jeor is now considered more accurate for most people. Harris-Benedict is still widely used and taught, and the 1984 revision is what this calculator runs:

For men: BMR = 88.362 + (13.397 x weight in kg) + (4.799 x height in cm) - (5.677 x age)

For women: BMR = 447.593 + (9.247 x weight in kg) + (3.098 x height in cm) - (4.330 x age)

The equations take kilograms and centimetres. This page asks for pounds and inches because most people who look this up think in those units, so it converts first and shows you both numbers in the result, letting you check the arithmetic by hand if you want to.

Multiply BMR by an activity factor to get your Total Daily Energy Expenditure (TDEE):

• Sedentary (desk job, no exercise): BMR x 1.2
• Lightly active (light exercise 1-3 days/week): BMR x 1.375
• Moderately active (moderate exercise 3-5 days/week): BMR x 1.55
• Very active (hard exercise 6-7 days/week): BMR x 1.725
• Extra active (physical job + daily training): BMR x 1.9

BMR accounts for roughly 60-70% of total daily energy expenditure for most people. Physical activity adds 15-30%, and the thermic effect of food (digesting your meals) adds another 10%.

The equations are population averages with meaningful individual variation. Actual BMR can differ from the formula by 10-15% depending on genetics, hormones, lean muscle mass, and other factors. If you are tracking calories and not losing weight as expected, your actual BMR is likely lower than the formula predicts.

One caution about the 500-calorie-deficit line in the result. That figure comes from the rule of thumb that a pound of fat carries about 3,500 calories, so 500 a day for seven days loses roughly a pound. Subtracting a flat 500 works for most adults and breaks down for small ones: a 100 lb woman of 70 with a sedentary job has a total expenditure near 1,240, and taking 500 off that leaves 743, which is below what anyone should eat without medical supervision. The calculator flags this when it happens rather than printing the number as advice. If you see the warning, take a smaller deficit and lose weight more slowly, or add activity instead of cutting further.