1. Enter your daily energy expenditure. You can use this calculator to get the value.
2. Set the "Daily intake" dial at the value you plan to aim for in your diet.
3. If the evaluation says you weight loss will be "High" or "Extreme" you should reconsider your plan.
Short term weight loss is primarily determined by the difference between caloric intake and caloric expenditure. As one lb of human body fat has a caloric content of approx. 3.400 kcal the average weight loss in fat can be reasonably estimated.
This calculation is however based on certain assumptions. First of all one assumption is that all your weight loss is fat. In the beginning of a diet most people will typically also lose body water and the weight loss will therefore initially be higher.
If the daily caloric deficit is too high (i.e. >1.000 kcal/ day), most people will typically also lose muscle mass. In short term this will increase the weight loss, but in the long run this will be an unwise strategy as your resting metabolic rate and your physical capacity goes down, which will make it more difficult to maintain the weight loss.
For a healthy weight loss, you should generally aim for a daily caloric deficit between 300 and 1.000 kcal. Some of this deficit should ideally come from an increase in physical activity.