I write it all in a little calendar I keep in my purse. It is definitely easier after having been doing this for a couple of years. I know how many calories are in the things I eat for breakfast and lunch, and I know how many calories are in our regular recipes for dinner. If it's a new one, I just plug it all in to the calorie count recipe analysis:
http://caloriecount.about.com/cc/recipe_analysis.php and see if it's 'affordable'.