When is a Religious Belief Delusional?

[GUBU]

Any belief is delusional when it goes against established evidence. Therefore all forms of the abrahamic religions are delusional (probably most other religious beliefs too, but I'm not expert enough to say).

When something is believed true on no or insufficient evidence, but without evidence against, it is unfounded. For example if Democritus had proposed the Higg's boson it would have remained an unfounded belief until we had the ability to measure it.