Mifflin-St Jeor and Harris-Benedict are widely used equations for estimating basal metabolic rate, but each was developed from a different population and neither replaces observation of the individual client.
Compare how the equations work, where their estimates differ and how activity multipliers turn BMR into an initial total daily energy expenditure estimate.
For coaches, the most important practice is to treat any calculated target as a starting hypothesis and adjust it using adherence, weight trend, performance and client feedback.