They will charge you interest only when you do not pay your bills on time. As long as you are paying your bill within the payment window given to you, you will not incur additional cost (just the annual fees)I do not like to use credit card at all. this is why I prefer to use other payment solutions and payment processors that could enable me to store money or save money as well. The fact of the matter remains that you get charged a lots of interest if you use credit cards and I hate interest.