What BMR actually is#
Your basal metabolic rate is the energy your body burns doing nothing at all — keeping your heart beating, your brain running, and your body temperature stable. It is the floor of your daily calorie burn and typically makes up 60–70% of everything you expend in a day. Everything you do on top — walking, training, even digesting food — is added to this baseline.
Methodology#
This calculator uses the Mifflin-St Jeor equation: for men, 10 × weight (kg) + 6.25 × height (cm) − 5 × age + 5; for women, the same formula with −161 at the end. The Academy of Nutrition and Dietetics rates it as the most accurate predictive BMR formula for healthy adults — closer to measured values than the older Harris-Benedict equation for most people.
BMR is not your calorie target#
Nobody spends a day at complete rest, so you should never eat at your BMR by default — that would put most people in an aggressive deficit. To turn BMR into a daily calorie number, multiply it by an activity factor between 1.2 and 1.9 — or let the TDEE calculator do it for you, then plan a cut or a bulk from there.
What moves your BMR#
- Lean mass: muscle tissue is metabolically active, so gaining muscle raises your BMR — one of the quiet long-term benefits of lifting.
- Bodyweight: a larger body costs more energy to run. As you lose weight your BMR drops, which is why calorie targets need recalculating every few kilograms.
- Age: BMR declines slowly with age, largely because of gradual muscle loss — another argument for strength training as you get older.