Is it common to retake the GMAT? If so, what kinds of results are common?

It is less common than you might think. Studies show that approximately 21% of the exams are taken by those who are retesting. Of those re-testers, it is uncommon that they take the test more than 3 times in a given year. Regarding results, the average increase between tests is 30 points on the total score. It is not unheard of that scores can go down with repeat testing. Your increase will depend on how much preparation you do in between. If you prepare well enough, odds are you won’t be compelled to retest!