Most CFA candidates ask the wrong question. "How many mock exams should I take?" is less important than "how should I use the mocks I take?"
Quality over quantity
Taking six mock exams and reviewing them superficially will do less for your score than taking three and spending twice as long on the post-exam diagnostic. The review is where the learning happens — the mock itself is just the diagnostic tool.
Optimal timing
Tells you exactly which sub-topics to study next — and in what order.
Take your first mock four to six weeks before the exam, before you have finished studying all the material. This sounds counterintuitive, but an early mock gives you the most valuable data: which topics are your biggest gaps, so you can allocate the remaining study time effectively.
Take your second mock two to three weeks out. By this point you should have addressed your biggest gaps from the first mock. If the same sub-topics are still red, you have a problem that needs a different approach.
Take a final mock in the last week as a confidence check and timing exercise — not as a new diagnostic.
The review process that actually works
After every mock, go through every wrong answer. Not just the ones you guessed on — every single wrong answer. Read the explanation. Understand why your answer was wrong and why the correct answer is right. If you cannot explain it without looking at the explanation, you have not learned it yet.