There are a few ways to go about it.
I personally prefer online calculators as a baseline. You will need to figure your BMR and RMR both. BMR is the number of calories you'd burn if you stayed in bed all day. RMR is BMR plus calories burned through daily activity.
Check out some BMR calculators 1st:
Then use the Harris-Benedict formula to find RMR from there.
(or google for a RMR calculator that will do it all at once for you)
To determine your total daily calorie needs, multiply your BMR by the appropriate activity factor, as follows:
1. If you are sedentary (little or no exercise) : Calorie-Calculation = BMR x 1.2
2. If you are lightly active (light exercise/sports 1-3 days/week) : Calorie-Calculation = BMR x 1.375
3. If you are moderatetely active (moderate exercise/sports 3-5 days/week) : Calorie-Calculation = BMR x 1.55
4. If you are very active (hard exercise/sports 6-7 days a week) : Calorie-Calculation = BMR x 1.725
5. If you are extra active (very hard exercise/sports & physical job or 2x training) : Calorie-Calculation = BMR x 1.9
Now, to lose 2 pounds a week you want to create a total calorie deficit of 7000 for the week. Standard suggestion is 500 a day each from diet reduction and exercise. I prefer to not add my exercise into the equation when figuring RMR, so I can just slash 500 off that number and call it a day. YMMV.
There are simpler quick and dirty methods advocated around here too, that will work just as well IMO. I just don't recall if the numbers I am thinking of are right.
I want to say it's maybe 15 cals per pound to maintain and 10-12 to lose. But please wait on that until someone else can weigh in on it.