According to the Mayo Clinic in Rochester, Minnesota, so long as you are not more than 25 pounds overweight, this rule tells you approximately how many calories you can ingest and still lose one pound per week:

Multiply your weight (in pounds) by 10.

The result is the number of kilocalories (or Calories) you can ingest per day and lose approximately one pound per week. This is only a rule of thumb and will vary by metabolism, body fat percentage, activity level, etc., but it's a good starting point for would-be dieters.