It is my understanding that one is not a heretic until declared one by the Church. One may have unorthodox ideas, which may or may not be heretical, but the Church is the one to determine who is a heretic or not, and also what is a heresy.
I have seen on these forums, things called heretical, which were not, and people called heretics, without any reference to the Church declaring them to be so.
We should be careful that we approach these things with right judgment and in charity, and always with the mind of the Church. We should never toss these terms about loosely, as that undermines the seriousness of actual heresy. We, as, laypersons have no authority to determine either people as heretical, or beliefs, unless it has been previously determined by the Church.