How many calories should i eat a day to lose 30 pounds as quickly as possible?

No specific amount: It isn't that simple. There are 3,500 calories per pound. If you eat too little - your metabolic rate will drop. It is mostly about ration of calories burned and calories consumed. Eat healthfully. Try to eat at least 5 servings of vegetables & 4 of fruit per day. Increase nutritional fiber. Avoid refined sugar & junk carbohydrates. Avoid alcohol, sweetened juices, soda & caffeinated beverages.