What I have read is determine your BMR, which the formula is:
Women: BMR = 655 + ( 4.35 x weight in pounds ) + ( 4.7 x height in inches ) - ( 4.7 x age in years )
then once you have that number times is by how active you are and you get your daily caloric needs:
If you are sedentary (little or no exercise) : = BMR x 1.2
If you are lightly active (light exercise/sports 1-3 days/week) : = BMR x 1.375
If you are moderatetely active (moderate exercise/sports 3-5 days/week)
= BMR x 1.55
If you are very active (hard exercise/sports 6-7 days a week) :BMR x 1.725
If you are extra active (very hard exercise/sports & physical job or 2x training) := BMR x 1.9
Then subtract 500 from that number and you will lose. This is what I do. I hope this helps!! Good luck!!