Some mobile calorie counters for fast food include MyFitnessPal, Calorie King and MyNetDiary. All of these apps are free to download and use. They are available for iPhone and Android phones.
MyFitnessPal is a weight loss app that also includes a good diary function. To add fast food, go to the food diary and search the name of the food or the fast food restaurant. Click on the appropriate item to add it to the diary and see the calorie count. Calorie King is more specialized to fast food and has a large inventory of items. The benefit of this app is that a solid Wi-Fi connection is not required to use it. MyNetDiary is similar to MyFitnessPal where it also tracks weight loss and exercise in addition to food.