I'm 20 yrs old , female, 5'4, and 257 pounds. how many calories a day do i need to lose 57 pounds?

205 K calories: 57 lbs is 205,000 calories. Most people can only reduce caloric intake by max of 500 cal per day. intense physical exercise burns about 600 cal/ hr. You can try the math using various amounts of caloric restriction and exercise. Bottom line: this will take a bit more than a year of an aggressive program of dieting and exercise.