Calorie goals can be determined several different ways.
Here are 2 of the easiest.
In my case, when I started my weight-loss project these 2 methods gave me the same number.
Don't go under 1200 calories per day unless you're supervised by a doctor!!!

Method #1 - Find your healthy goal weight and multiply it by 10.
This will bring you to your goal weight, and you only have to figure it out once.

Method #2 - Multiply your current weight by 10, then subtract 500-1000 calories per day to lose 1-2 lb per week.
(This method is used by my doctor & dietician.)
If you have a lot to lose, aim for 2 lb per week at first. When you're closer to your goal weight, slow to 1 lb per week.
This is a better method if you have a lot of weight to lose, because you're eating to maintain your current weight, which is likely lots more than what method #1 came up with.
Also, drastically changing your intake suddenly is not likely to be sustainable. You'll feel hungry all the time & be miserable.
The disadvantage to this is that you have to periodically recalculate... but it's very easy to do.

"evidence shows that people who lose weight gradually and steadily (about 1-2 pounds per week) are more successful at keeping weight off ...
To lose weight, you must use up more calories than you take in. Since one pound equals 3,500 calories, you need to reduce your caloric intake by 500-1000 calories per day to lose about 1-2 pounds per week."
http://www.cdc.gov/healthyweight/losing_weight/index.html