It’s arguable that no grades matter as a first principle; they matter only insofar as they provide some evidence that one has mastered the material in the course and fulfilled its requirements (which may include, say, turning in work on time). This could have implications for future educational opportunities or employment.

In a Ph.D. program, grades do not matter at all beyond fulfilling the minimum requirements (if they exist). If you impress a professor in class, perhaps they will matter indirectly if said professor ends up on your committee or you’d like to collaborate with them. Or not. No one cares about your grades.

What matters more is what you research, its contribution to relevant scholarship and fields, and the degree to which it aligns with the agenda of the organizations you plan to apply to. Also, given the competitive environment, how well you can demonstrate that you can balance this with other schedules, e.g., publications, grant money-raising, visiting fellowships elsewhere, maybe teaching is also really important. In other words, can you demonstrate that you can stay on top of your thesis while doing other meaningful scholarly work simultaneously?

Every certified credential is valuable for following a career so is a Ph.D. Now, as for grades, especially for a Ph.D., research value and paper awards matter more than grades. For Bachelor’s and Master’s, grades should matter primarily.

Here’s the other side of the “grades don’t matter” canard or trope:

1. First, you can’t keep your scholarship or position in the program without a certain GPA.
2. It’s worth mentioning that if you don’t have the passion for learning the basics of the discipline, which is to say, get at least decent grades; it is hard to have a quality dissertation.

In most countries, Ph.D. students don’t take any courses. Canada and the United States for example are exceptions, but it is a rule in other countries. Second, you need to pass and meet your advisers’ expectations. In the programs, a B is a passing grade; in some Ph.D. programs, two C’s would earn you a quick end to your time in the program. Third, most faculty members never look at grades when reviewing applications; grades don’t matter to them.

Grades matter during your time as a student. All programs in the US have a minimum GPA that must be maintained to stay in good standing. The GPA required for core classes may be higher than the overall GPA. After you have graduated with a Ph.D., grades will only matter if you are seeking your first job with a commercial company that is just seeking people who are smart and are ignorantly playing averages. Everywhere else (universities and companies which understand the value of a Ph.D.) will look at your publications, not your GPA.