Here is the answer from the creator, Mr Peter Stallo CRNA about how the PACES board review program calculates your % to pass boards on 1st attempt:

The calculation is derived from the results of students who obtained their test scores from their school and the relative the difficulty level of the questions in the board exam versus the difficulty level of the PACES exams. The board exam is adaptive and will present easy questions during the course of the exam. The PACES questions remain at a high level throughout the exam (there's no sense in my asking you the MAC of desflurane). Also, you should note that the distribution is predicted along a bell curve that is truncated at 5% and 95%. This is done to normalize the distribution across the population of students. It is truncated because there is no way I can predict that any particular student will DEFINITELY pass or fail.

It is impossible to state how many questions you must answer correctly because you can answer fewer difficult questions and achieve a higher score than if you answer several moderate questions correctly but miss an easy question.


This doesn't directly answer your concern, but it is done to help alleviate or direct your concern. If PACES is telling you that there is a significant chance you will fail, I would try a different approach in your studying before time to take the test.