How many calories should I be eating and/or burning if I want to lose 10-20 pounds in a month?

I have been keeping track of my calorie in take for the past week, it has ranged from 1200- 1450.
I have also been keeping track of how many calories I have burned, which is anywhere from 100- 700 calories a day.
Now, I don't know what my goal should be for each day. As in how many calories I should be taking in, and how many I should be taking out.
Pls help!
Thanks!