Answer:

You can estimate your basal metabolic rate by using the Harris-Benedict equation. The BMR is the rate at which your body burns calories to sustain life and is roughly 50-80 calories per hour in most people, which is 1,200 to 1,920 calories burned all day. If you were to lie in bed all day, you would burn whatever your BMR is (your BMR depends on genetics, muscle mass, and a number of other factors).

Now, if you exercise for 60 minutes and burn 400 calories, then during that hour, you burn the 400, plus your BMR. If your BMR is 60 calories per hour, then you burned 460 calories during the hour of exercise. And if you walk home from the gym instead of drive, then you will burn even more. So at the end of the day, when you add it all up, if your total daily energy expenditure is greater than the number of calories you've eaten, then you lose weight.

For women, the basal metabolic rate =
655.1 + (9.563 x kg) + (1.850 x cm) - (4.676 x age)

Then you need to factor in your activity level.
If you are Sedentary (little or no exercise)
Calorie-Calculation = BMR X 1.2
If you are Lightly Active (light exercise/sports 1-3 days/week)
Calorie-Calculation = BMR X 1.375
If you are Moderately Active (moderate exercise/sports 3-5 days/week)
Calorie-Calculation = BMR X 1.55
If you are Very Active = BMR X 1.725 (hard exercise/sports 6-7 days/week)
Calorie-Calculation = BMR X 1.725
If you are Extra Active (very hard daily exercise/sports & physical job or 2X day training)
Calorie-Calculation = BMR X 1.9

Here's an example:
You are 32 years old
You are 5 feet 4 inches tall (162.5 cm)
Your weight is 185 pounds (84 kilos)
Your BMR is 655 + (806) + (291) - (150) = 1602 calories

Here's the Harris Benedict Formula for Men:
BMR = 66 + (13.7 X weight in kilos) + (5 X height in cm) - (6.8 X age in years)

Then you need to factor in your activity level.
If you are Sedentary (little or no exercise)
Calorie-Calculation = BMR X 1.2
If you are Lightly Active (light exercise/sports 1-3 days/week)
Calorie-Calculation = BMR X 1.375
If you are Moderately Active (moderate exercise/sports 3-5 days/week)
Calorie-Calculation = BMR X 1.55
If you are Very Active = BMR X 1.725 (hard exercise/sports 6-7 days/week)
Calorie-Calculation = BMR X 1.725
If you are Extra Active (very hard daily exercise/sports & physical job or 2X day training)
Calorie-Calculation = BMR X 1.9

Here's an example:
You are 25 years old
You are 6 feet tall
Your weight is 220 pounds
Your BMR is 66 + (1370) + (914) - (170) = 2,180 calories