Calorie Defecit

Calculate your TDEE (total daily energy expenditure) based on activity level, age, height, gender, and current weight. That should give you a baseline caloric intake. What you burn each day in calories. If you want to create a deficit, aim for something below that TDEE.

where do i go to calculate those numbers

First calculate your BMR (Basal Metabolic Rate). It's the amount of calories you burn everyday for essential bodily functions that don't involve motion (breathing, organ function, brain function, etc). The formula to find your BMR is this:

BMR = 370 + (21.6 x LBM)............Where LBM = [total weight (kg) x (100 - bodyfat %)]/100

For example, I weigh 185 pounds, and have a body fat percentage of 18%

To find my BMR, I'd convert 185 pounds to KG, and I get 84 kg. I then multiply 84 by 0.82 to get my lean body mass in kg which is about 69kg. I multiply 69 times 21.6 and add 370 to that to get a BMR of 1860 calories.

Once I know my BMR, I just have to multiply it by an activity factor to get my TDEE. The activity factors are:

1.2 = Sedentary (Desk job, & Little Formal Exercise)
1.3-1.4 = Lightly Active (Light daily activity & light exercise 1-3 days a week)
1.5-1.6 = Moderately Active (Moderately daily Activity & Moderate exercise 3-5 days a week)
1.7-1.8 = Very Active (Physically demanding lifestyle & Hard exercise 6-7 days a week)
1.9-2.2 = Extremely Active (Athlete in ENDURANCE training or VERY HARD physical job)

I chose 1.4 to be conservative which gives me a TDEE of 2600 calories a day. Since I want to lose weight, I subtract 20% of the calories for weight loss, and that leaves me with a daily calorie goal of about 2100 calories a day. It might be confusing, but it's the best way to go about it.