I wrote this up for another poster a while back:
The Katch McArdle formula is pretty accurate for determining your caloric needs (if you know your bodyfat%):
BMR (Resting Calories) = 370 + (21.6 x LBM)
Where LBM = [total weight (kg) x (100 - bodyfat %)]/100
And then multiple that number by the following:
1.2 = Sedentary (Little or no exercise and desk job)
1.3-1.4 = Lightly Active (Little daily activity & light exercise 1-3 days a week)
1.5-1.6 = Moderately Active (Moderately active daily life & Moderate exercise 3-5 days a week)
1.7-1.8 = Very Active (Physically demanding lifestyle & Hard exercise or sports 6-7 days a week)
1.9-2.0 = Extremely Active (Hard daily exercise or sports and physical job)
(note: make sure you're not just considering work outs but also your lifestyle)
If you don't know your BF%, there's always this: http://www.bmi-calculator.net/bmr-calculator/
Additionally, there is a simpler formula which is:
Body weight x 14 = rested caloric needs (i.e. the calories you burn everyday by doing virtually nothing)
Then you multiply that number by your activity factor (same standards as in the above more complicated formula).
In order to lose weight, you have to eat below your maintenance. I would recommend something like starting with a 200 calorie deficit and tracking your weight loss for 2-4 weeks. If you start losing at a healthy rate, continue eating at that number until the weight loss stalls and then decrease your calories by another 200.
You should also be sure to be eating a higher protein diet while you're in a deficit and I recommend tracking your macronutrients as well. If you want more information on that, let me know.
Hope this helps.