A rigid or fixed calorie number does not work for all individuals and even the same individuals on different days depending on their level of activity. Hence it must be customized considering different variables.
The above calculator will arbitrarily measure the number calories you need to consume to maintain your current weight or lose some pounds. Post your fair estimate of the number of times you exercise and the intensity and be honest about it
As you gradually start to drop weight, a recalculation will be needed to estimate the calorie count. A change in workout intensity will also need a recalculation based on increased energy needs.
3500 calories equals a pound of fat so theoretically a 500 cal deficit per day should lead to loss of 1 pound of fat per week. In practice things are different. Initial fat loss will be quick but as soon as your body becomes more efficient at using energy ( you becoming fitter) , the pace of calorie burn will start to drop until you hit a plateau. Now the same calorie deficit and same exercise will only help maintain current weight instead of lose more weight.