how many calories per day- please give advice

does anyone have a reliable website where i can calculate how many calories i should eat a day to loose weight, right now mfp has it set at 1200 cal a day, but i think that was a number i put in not what mfp suggested and i dont know how to gat an accurate amount, when i looked on other sites off of google, they are saying 1500 calories a day...
i am 23 years old weight 172 and am 5ft 1in.. i would like to lose 30 pounds within 3-4 months.
also i dont understand something, assume i were supposed to consume 1500 cal per day, now i should eat at a deficit i have seen on many posts on here, so should i only eat 1000 cal a day, and workout or should i eat 1500 cal and burn 500 a day? OR should i be eating 2000 cal and burning 500 to equal the 1500?
advice would be very helpful, i think i am doing this whole thing wrong, because i am eating 1200 cal a day, working out about 5 days a week now for over a month and eating pretty clean, and im only gaining...