BMR accounts for roughly 60–70% of total daily energy expenditure for most sedentary adults. It is influenced by body size, lean muscle mass, age, sex, and thyroid function. Muscle tissue burns more energy at rest than fat tissue, so a higher lean mass raises BMR.
Commonly used prediction equations — Mifflin–St Jeor, Harris–Benedict — give estimates within roughly 10–15% of measured values for most people. Actual BMR can only be measured precisely in a clinical setting.
Total daily energy needs add physical activity (exercise and NEAT) and the thermic effect of food on top of BMR. Use the calorie needs calculator for a personalised estimate, keeping in mind it is a starting point rather than a precise target.