I believe there are some guides at to what people are making in your area. I know AIGA publishes one for graphics, i cant remember for ID. Basically you have to think what is the minimum I want to take in profit and then determine the scope of what your overhead is ( both in general for operating and for each specific project) Its all a hypothetical, you will only be able to know if your charging the right amount if you have your overhead covered and the clients accepts your proposal. Basically I started off charging way too little, figuring i just wanted to get the work. Now I take into consideration what my yearly profit goal is subtract COGS, indirect expenses. I promise you will not get the right rate at first.