As a woman of your current weight you probably need about 2000 cals a day to maintain your weight. One pound of "fat" weighs about 3600 cals. So if you stuck to 1500 cals per day, every 7 days (ish) you would burn up enough stored fat to lose a pound. This is the basic maths but bodies are more complex than this. You will probably have stored water that will show a bigger weight loss in the first week (but this will come back when you go back to eating normally so it can make it a bit confusing). But if you know you are eating less calories than you are using, then you are burning your reserved fat. This is why most calorie counting diets suggest 1000-1500 cals per day. I think its best to start at the higher end of this and leave yourself some manoevering room for later on if you find your weight sticks. Then at the end when you have successfully lost your weight you can slowly build back up to the 2000 per day. This is the essence of most diets. If you add in exercise then you can add a few more calories or just let yourself burn the fat quicker. Easy-peasy huh? Good luck!
Judi x