Agreed. I almost always double my estimates, and if it's a bigger unknown project, triple it. You can do fixed cost, but make sure that you have a fixed set of

Agreed. I almost always double my estimates, and if it's a bigger unknown project, triple it. You can do fixed cost, but make sure that you have a fixed set of features that you both agree on and an hourly rate for scope creep (which will happen as soon as they see anything). Or keep it entirely hourly, in which case, some scope creep might be welcome on your end.