The Mifflin-St Jeor BMR formula
BMR is the number of calories your body burns at rest. The Mifflin-St Jeor equation, published in 1990, is widely regarded as the most accurate of the common estimates:
men: BMR = 10·kg + 6.25·cm − 5·age + 5
women: BMR = 10·kg + 6.25·cm − 5·age − 161
Weight is in kilograms, height in centimetres and age in years. US units are converted automatically (1 in = 2.54 cm, 1 lb = 0.4536 kg).
Worked example
A 30-year-old man, 178 cm, 75 kg:
10 × 75 = 750.
6.25 × 178 = 1112.5.
−5 × 30 = −150, then +5.
BMR: 750 + 1112.5 − 150 + 5 ≈ 1,718 kcal/day.
What BMR actually measures
BMR is the energy for involuntary functions — breathing, circulation, cell production, brain activity — measured while lying still in a fasted state. It typically accounts for 60–70% of the calories you burn in a day. Add your daily activity on top and you get your TDEE (total daily energy expenditure), which is what you actually eat against.
Note: BMR is an estimate. Body composition, genetics and hormones all shift it, and equations can't capture an individual's exact metabolism — but Mifflin-St Jeor is reliable for most people.