There are many paths up the MBA mountain, but almost every GMAT student takes the same first step: the diagnostic test. This is perfectly logical. You should learn about your own strengths and weaknesses before you carve out your own goals, expectations, and plans. Everyone would love to earn a perfect score, but it’s hard to come up with the best plan for you if you have absolutely no idea what scores you’ll be aiming for, and therefore what kinds of schools you are likely to be admitted to. So most everyone starts their GMAT prep with a diagnostic test. But which diagnostic test should you use? Are all diagnostic tests created equal?

Because it has the reputation and authority of being the official prep materials created by the GMAC—the larger corporation that designs and administers the GMAT—the diagnostic test contained in the GMAT official guide is the diagnostic test many, if not most GMAT students take. Here, we tell you everything you need to know about that diagnostic test, so you can decide if it’s the one for you.


The diagnostic test contains 100 total multiple-choice questions, representing both the verbal and quantitative sections of the test. These questions, like all the questions in the Official Guide, are real GMAT questions taken from past exams—which isn’t true for any other product on the market.


Note: The Official Guide’s Diagnostic Test IS NOT meant to be an actual practice/simulated version of the GMAT. Rather, it is a strategically chosen assortment of questions of varying difficulty and subject matter. As the OG itself states in the introduction to the Diagnostic Test, the test and its scoring system is designed to help you answer the question, “If all the questions on the GMAT exam were like the questions in this section, how well would I do?” And rather than simply assigning a numerical score, your results for each section are categorized as “excellent, above average, average, or below average” relative to other test-takers.

The ultimate purpose of this diagnostic test is ultimately to help you develop realistic goals and expectations for your results on the actual GMAT, and to help you plan your test prep accordingly. In addition to getting an idea of how well you might do overall, the section-by-section breakdown should help you design a study plan to build on strengths and target specific weaknesses.


One notable thing about the diagnostic test in the Official Guide is that it is untimed. This is one notable way that the OG’s diagnostic test differs from, say, a practice test, or any other hypothetical diagnostic test that attempts to determine your ability to navigate time constraints. This is because the OG’s diagnostic test is more designed to help you get a broad overview of your problem-solving capabilities relative to your peers for each subject. It isn’t designed to take time constraints into account.


As we mention above, the OG’s diagnostic test is the only diagnostic test that uses actual GMAT questions for its diagnostic test. This makes it an inevitably superior diagnostic test in its correspondence to the actual subject matter and wording of the actual GMAT test. Even the formatting and diagrams are the same as you can expect to find on the actual GMAT. Because of this singular authority, the quality of the OG’s diagnostic test at least in terms of the questions themselves is beyond comparison.

The quality of the solutions and the explanations provided is more a matter for debate. On the whole, we find that these components of the OG are MOSTLY adequate for MOST students. The explanations tend to be clear and understandable. However, there is only one solution given to each problem, and it’s seldom explained in much detail.

This means that there are some solutions that students will struggle to understand, especially if the student’s problem-solving instincts & abilities don’t line up perfectly with the method favored by the OG. Because (as you will hopefully learn early in your GMAT prep) every problem has more than one way by which the solution can be determined—and every student has their own learning and problem-solving style. Therefore, the solutions to the problems in the OG’s diagnostic test are somewhat limited in their utility for learning the material you had difficulty with.

However, the diagnostic test is designed less to immediately teach you any particular concepts, and more to help you determine where your difficulties lie, exactly, so you can target them as you move into your prep.


If you take the OG’s diagnostic test at face value—which means you are approaching it primarily to learn where to focus your prep energies to best target your weaknesses in terms of the GMAT’s subject matter—then the test’s insights are very valuable. Having a diagnostic test based on actual GMAT questions is a priceless resource.

The OG’s diagnostic test is particularly successful at predicting students’ ultimate testing capabilities. The OG’s intro to the diagnostic notes that the statistical reliability of the diagnostic test in predicting GMAT-takers’ ultimate scores ranges from 0.75 to 0.89, and they rate their “subscale classification” at 85-90% accurate. If there are any other diagnostic tests that can credibly claim statistically superior reliability, we aren’t aware of them.

As we’ve mentioned, the value of the diagnostic test in terms of its instruction in the GMAT’s actual subject matter isn’t especially noteworthy, but that’s not really the point of the diagnostic test.

One possible limitation of the diagnostic test is that it differs in obvious ways from some of the testing conditions of the actual GMAT. The 100=question diagnostic test is obviously not structured exactly like the GMAT. The diagnostic test is deliberately untimed, where some students may find it useful (and increasingly reliable, as a score diagnosis) to factor the ability to answer questions in a timely manner into their initial score diagnosis.

Further, the diagnostic test in the OG is a standard paper-based test with a linear structure. The actual GMAT, on the other hand, is a Computer Adaptive Test. So not only are you taking it on a computer (which some students may prefer for their diagnostic test) as opposed to taking it on paper—you are also being given questions whose order and difficulty level corresponds to your performance as you go. The printed OG’s diagnostic test doesn’t mimic the actual GMAT in these ways, which some students may find important information to include. If you fall into this category, there are several electronic diagnostic tests you can choose instead of, or in addition to, the OG test.



The OG’s diagnostic test does have some limitations, and there are some important ways it differs as a test-taking experience from the actual GMAT. However, the ultimate purpose of the diagnostic test is to provide a realistic portrait of a student’s current scoring prospects on the actual GMAT—the purpose is not exactly to simulate the GMAT itself.

Whatever shortcomings the OG’s diagnostic test has are minor, especially considering the statistical reliability it can promise for its results. It’s also, in many ways, an unparalleled resource for drawing conclusions about the actual GMAT, because no other diagnostic test can promise questions that correspond so directly with actual GMAT questions. At the end of the day, the point of the diagnostic test is more about diagnosing than teaching (the teaching comes later, after the diagnostic test), and in that regard, no GMAT prepper will go wrong starting with the diagnostic test in the Official Guide.