The average number of calories that a woman burns in a day primarily depends upon her activity level and personal factors such as her age, weight and height. Men and women use separate formulas due to differences in their metabolic rates. You need to know your daily calorie expenditure in order to predict your weight-loss rate.
Basal Metabolic Rate
The basal metabolic rate, or BMR, is the rate at which you burn calories when you're not performing any activity in all. Your BMR assumes you're not using calories to digest food or regulate your body temperature.
Harris-Benedict Equation
The Harris-Benedict equation is a formula that calculates the BMR for each gender. Weill Cornell Medical College provides the Harris-Benedict equation for women as follows: BMR = (9.563 x Weight) + (1.850 x Height) - (4.676 x Age) + 655.1. This equation requires your weight in kilograms and your height in centimeters. It provides your BMR in calories per day.
Limitations
The Harris-Benedict equation does not consider your body-fat percentage. Muscle requires more energy to maintain than fat, so this equation underestimates your BMR if you have a low body-fat percentage. Similarly, it overestimates your BMR if you have a high body-fat percentage.
Activity Level
The calculation of your average daily calorie expenditure requires you to estimate your activity level. Your BMR corresponds to an activity factor of one. By comparison, a moderately active person has an activity factor of 1.55.
Calculations
Multiply your BMR by your activity factor to obtain the average number of calories you burn in a day. For example, assume you weigh 67 kg, have a height of 169 cm and are 31 years old. Your BMR is (9.563 x 67) + (1.850 x 169) - (4.676 x 31) + 655.1 = 1,464 calories per day. You're moderately active, so you have an activity level of 1.55. Your daily calorie expenditure is therefore 1,464 x 1.55 = 2,268 calories per day.
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