Your Basal Metabolic Rate or BMR is the minimum amount of energy that your body requires to function at rest (imagine you sleeping on a bed for 24 hours). It is expressed in calorie terms. The standard for calculating the BMR is the Migglin St. Jeor Equation and is different for men and women.
For men BMR is 10 x weight (kg) + 6.25 x height (cm) – 5 x age (years) + 5
For women BMR is 10 x weight (kg) + 6.25 x height (cm) – 5 x age (years)- 161
So from this, it is clear that your height, age and gender matter. Also, since your muscle mass declines by 5-10% every ten years after the age of 30 (unless you do strength training), your metabolic rate slows down after 30 i.e. the total energy you require after 30 starts to fall. Understanding your BMR is important as it gives you a base level of energy that you need to function.
The minimum calorie intake required for a human being is your BMR x 1.2 (little or no exercise) and up to BMR x 1.9 for heavy exercise (twice per day extra workouts). For most of us who may be engaging in moderate exercise 3-5 times a week, your minimum intake is BMR x 1.55.