Step one: Basal Metabolic Rate (BMR)
BMR estimates the calories your body burns at complete rest. For a 70kg, 170cm, 30-year- old man: BMR = 10×70 + 6.25×170 − 5×30 + 5 = 1,618 kcal/day, using the Mifflin-St Jeor equation (the most widely validated BMR formula in current clinical use).
Step two: scaling up by activity level
BMR alone assumes total rest — it doesn't account for daily movement or exercise. Multiplying it by an activity-level factor (1.55 for "moderately active," 3-5 days a week of exercise) gives Total Daily Energy Expenditure (TDEE), the maintenance calorie figure: 1,618 × 1.55 ≈ 2,507 kcal/day.
Why men and women use different BMR formulas
The Mifflin-St Jeor equation subtracts a different constant for men (+5) versus women (−161), reflecting average differences in body composition between sexes at the same weight and height — a simplification that works reasonably well at the population level, though individual metabolisms vary.
Why this figure is the foundation for weight goals
Maintenance calories are the reference point every calorie-based weight goal is built from — eating below it produces a deficit for weight loss, and eating above it produces a surplus for weight gain, both covered directly in the companion article on calorie goals.