I don't think it's quantity so much as quality. I mean, I would at least take 4, but what will matter more is how you learn from those tests. Carefully review your mistakes, and compare them to the mistakes you made while doing untimed practice, and revise your study plan as you go to attack your weaknesses. Just make sure you don't neglect so your strengths....they can become weaknesses if you don't practice them too!

quality over quantity is definitely right.

I'm in the minority, but I have my students (except in rare cases) take exactly two: the two GMATPrep exams. All other practice exams aren't worth the large amount of time it takes to take them, recover from them, and review them, when you could be looking at fresh questions that are more relevant to you.

I took six practice tests - the two GMATprep tests and four from MGMAT. I would recommend taking at least four tests. In my opinion, you should take a GMATprep test before you start studying. This will give you a baseline that you can base your progress/study habits off of. I would save the second GMATprep test for a couple of weeks before the actual GMAT. As for the other two tests, I would use them to work on timing and to get a feel for what the test will be like (i.e. stamina). If you are having problems with timing, like I was, I would definitely take more. Here is a more detailed breakdown of my practice test scores.


https://www.beatthegmat.com/viewtopic.php?t=4900

Just want to add that this site is just awesome!