Trial and error is your best bet. Everyone has different metabolisms, genetics, daily amounts of exercise etc.

Just make a 2000 calorie diet and try it for two weeks, check how much weight you've lost and if it's >0.5KG <1KG per week then stick with the diet and if it's not then just adjust your calories accordingly.

We need more information to help you though, like do you go the gym? How long have you been going for? Bodyfat % estimate?

You should have posted this in the sports section though, some of the advice on this thread is absolutely terrible.