BMR vs TDEE
BMR is the energy your body uses at complete rest. TDEE multiplies it by an activity factor to estimate real daily burn. Eating roughly at TDEE maintains weight; sustainable change usually means modest adjustments from there.
About the equation
The Mifflin-St Jeor equation is the standard used by dietitians because it tracks measured metabolism most closely across body types. It is still an estimate — individual metabolism varies around ±10%.