The largest contributor to the calories we expend each day is our basal metabolic rate (BMR), which is the energy our body requires to maintain basic physiological functions such as breathing, circulation, and organ function while at rest.
BMR accounts for about 60-70% of the total calories we burn each day. Physical activity, such as exercise and movement throughout the day, can contribute to the remaining 30-40% of the calories we expend. The exact percentage of calories contributed by BMR and physical activity can vary depending on an individual's age, gender, body composition, and level of physical activity.