I go by this formula my trainer gave me:
Weight x 10 calories per pound and .75(75% calories) = calories to eat.
so 245 x 10 x.75 = 1838 calories.
Then for every 10 lbs re-evaluate your calories.
This obviously isn't for someone who is like 120 lbs or something but for someone who has a decent amount of weight to lose.
You've already lost 50 lbs so you are obviously doing great!