Hmm as far as I know the calories you should eat are based on your weight/height etc... however most people eat between 1000-1500 calories on average. Very large people can start off with 1,900 and move it down gradually, and less than 1000 is not meant to be good for you really unless you are following one of these nutritionally devised replacement programmes.
If you stick to somewhere between 1000-1500 calories every day and continue to exercise regularly 3-5 times a week (not obsessively) your weight loss should be more or less consistent!