Do you know how much you've been eating daily for the past few weeks? Have you been losing weight, maintaining, or gaining weight during that time?
If you don't know how much you're eating, track it for 2 weeks and track your weight. If your weight is going down, keep it. If it's not, lower calories by 300 daily and reassess in 2 weeks.
Basically, pick a number (err on the side of possibly slightly higher than you think) and monitor for 2 weeks and reassess.