I generally don’t count calories, but once in a while I find them helpful as a marker.
Before going any further, I want us all on the same page so let’s start with a quick definition of a calorie. By definition a calorie is the energy it takes to raise the temperature of 1 gram of water 1 degree Celsius. In short, a calorie is energy. It is a way to measure the energy that fuels our bodies. What a calorie will not tell you is whether or not that calorie came from a nutrient-dense food or if it came from some pretend food like deep fried butter balls. This is the basic reason why I would never encourage anyone to only look at calories.
But calories have a place as one indicator in our tool kit for fueling our bodies. In particular relation to weight loss or gain, it takes an excess of 3500 calories above your needs to gain one pound. Likewise you have to reduce your calorie intake by 3500 calories to lose one pound. But how many calories do you need to begin with?
Even if you stayed in bed all day you would burn a certain amount of calories. This is your Basic Metabolic Rate, or BMR. Once you know your BMR you can use the Harris Benedict Equation to find the approximate value of how many calories you need based on your level of activity. To find your BMR with the Harris Benedict Equation, you could use this online calculator : http://www.muscleandstrength.com/tools/bmr-and-daily-calorie-calculator.html
Using that particular calculator my daily calorie requirements are around the 2300 calorie range. I find it helpful to check in once in a while to make sure I am eating that appropriate amount. I frequently use this website to look up caloric values: http://caloriecount.about.com/. When it comes to weight loss I have found that once I go below 1900 calories/day for a few days I will likely find myself on a binge. For whatever reason my body is not a happy camper below that point. Therefore when I need to lose a few pounds (i.e. if I have spent a few weeks overindulging over the holidays) I know I can easily do it by cutting about 400 calories per day. That means it takes me a little more than a week to lose a pound, which might not sound exciting, but it is the point at which my body is happy to work with me. If I go below 1900 calories that is the hard way to lose weight. I am miserable and I will self-sabotage by eating 6 ice cream bars after the children are in bed or eating a half jar of peanut butter with a spoon. I would encourage you to find out what range you should be eating in and check in once in a while to see how you are doing. It is just one way to gauge things and I personally find it helpful.
One caveat, calories listed in food (anywhere) are not an exact science. They are an approximation, because food items can vary. That said, it is still helpful to figure out how much you are eating as compared to how much you should be eating. Finally, remember you should be getting these calories from lean protein, fresh or frozen veggies/fruit and whole grains not from processed or fast food sources.