How many calories should I eat?

Hi all,

I've lost 51 lbs so far but I've noticed lately that I have been plateauing. Naturally this calls for a change in my allotted calories, but I can't seem to find a consistent number between all the various online calculators. Currently mfp is saying that I need to be eating 2000 cals a day to lose one pound a week, but that no longer seems to be doing it. I'm Male, 24, 5'9, 224 lbs and I don't exercise a lot due to work. On some of these calculators i'm getting 2100 calories per day, while others are saying 2400. It's quite confusing.. help!

-Marc