Can you please tell us your age and current weight ?
Based on your age and current weight you know how many calories your body burns every day for vital functions.
To that amount add the exercise calories and then substract 1000. This amount will help you to lose 1kg of fat per week ( 1kg = 2.2 pounds, 1kg = 7000 calories ). If you don't add the exercise calories, then substracting 1000 will bring you under 1000 calories you should eat every day which is not recommended at all. This is why it is so hard to lose weight without exercises.
If you are, for example, a 24 yo female at 160lbs, your calories consumed per day by vital functions are 1561 in number ( According to the calculator at http://www.calotor.com
), if you eat 1200 then you will lose only 300/day which is 1kg every 3 weeks. It is not that bad if you are only 160 pounds, but i bet you want to lose some fat faster than that.
On the other hand, as i told you, going under 1000 will affect your health, so the only way to real lose weight is to do good exercises and to eat less than the total number ( bmr + exercises ).
If instead you are a 19 yo boy at 300 pounds, your BMR will be 2747 so you can eat only 1500 calories a day and lose weight without exercises.