BMR Calculator

BMR (Basal Metabolic Rate) is the number of calories your body burns at complete rest just to keep vital functions running -- breathing, circulation, cell repair. TDEE (Total Daily Energy Expenditure) is BMR multiplied by an activity factor, so it includes everything else: walking, workouts, digestion, daily movement. BMR is the floor; TDEE is the number that actually reflects a full day, and it's the one this calculator uses for weight loss and gain targets.

Mifflin-St Jeor is the default here because a 2005 systematic review found it predicted resting metabolic rate more accurately than Harris-Benedict in both non-obese and obese adults. Harris-Benedict, from 1918, tends to run about 5% higher against modern measurements. Katch-McArdle is worth switching to only if you have a real measured body fat percentage -- it uses lean body mass instead of height and sex, which makes it more suitable for very lean or muscular people. Without a body fat number, this calculator falls back to Mifflin-St Jeor rather than guessing.

It starts from your TDEE (BMR × activity factor), then applies your chosen goal rate: 7,700 kcal per kg of body fat, which is 1,100 kcal/day per 1 kg/week of change, so a 0.5 kg/week goal shifts the target by about 550 kcal. For weight loss, that target is checked against a safety floor -- it will not display a number below 1,200 kcal/day for women or 1,500 kcal/day for men, raising the target and flagging it if your requested rate would go lower.

These are population regression equations, so an individual's actual resting metabolic rate typically sits within about plus or minus 10% of the prediction, and can be off by more at extremes of body size. The biggest source of error in your final calorie target usually isn't the BMR formula -- it's the activity level, since most people overestimate how active they are, and one category too high can mean several hundred calories a day.

The classic '3,500 kcal per pound' (about 7,700 per kg) rule treats your body as a fixed machine, but it isn't one. Research published in The Lancet (Hall et al., 2011) showed that a sustained calorie deficit triggers metabolic adaptation, so the same deficit produces progressively less weight loss over time. Use the target this calculator gives you as a starting point, then track your actual weight for 2-3 weeks and adjust -- that's the only real calibration.