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BMR is the number of calories your body burns at rest to maintain basic functions like breathing, circulation and cell production. It accounts for about 60-75% of total daily calorie expenditure. Even if you stayed in bed all day, you would burn your BMR in calories.

TDEE (Total Daily Energy Expenditure) is your BMR multiplied by an activity factor. It represents the total calories you burn in a day including exercise and daily activities. The Mifflin-St Jeor equation calculates BMR, then multiplies by factors ranging from 1.2 (sedentary) to 1.9 (extra active).

The Mifflin-St Jeor equation, published in 1990, is considered the most accurate BMR estimation formula by the Academy of Nutrition and Dietetics. It is more accurate than the older Harris-Benedict equation, especially for overweight individuals.

In theory, a 500 calorie daily deficit creates a 3,500 calorie weekly deficit, which approximates 1 pound of fat loss. In practice, weight loss is not perfectly linear due to water retention, metabolic adaptation and other factors. It is a reasonable starting target for gradual, sustainable weight loss.

Generally no. Eating below your BMR for extended periods can slow your metabolism, cause muscle loss and lead to nutritional deficiencies. Most health professionals recommend not going below 1,200 calories/day for women or 1,500 calories/day for men without medical supervision.