Scores can vary widely, but they tend not to. The test maker presents two statistics on the subject that tell slightly different stories.
First is the reliability of the test. The GMAC says that you are 92 percent likely1 to get the same score on the GMAT if you take the test and then retake it, unless your skills have improved or deteriorated in the interim. So there is little reason to retake the GMAT in the hope of improving your score by chance. If you retake the test, plan to do substantial preparation to improve your score.
The standard error of measurement also gives you some perspective on score improvement. Your score on the GMAT is an estimate of the “true” score of your ability, and the test maker says that “the standard error of measurement is 30–40 points” for the 200–800 score.2 This means that your score on Test Day may well be 30 to 40 points below your “true” score, or it may be 30 to 40 points above your “true” score. Thus, a score improvement of 40 points or more constitutes a major accomplishment. In other words, 40 points may or may not sound like a lot on the GMAT scoring scale to you—but it is a lot.