Q: how many calories do you burn doing jumping jacks for 15 mins

A: Doing jumping jacks for 15 minutes would burn around 150 calories or so. However I would advise NOT counting calories if you are looking to lose fat and weight, but instead following a complete weight-training, nutrition, and cardio program that will not only burn calories through exercises but also boost your metabolism to make sure you burn more fat around the clock just by going through your everyday routine. Please read my fat loss article to learn how.