Faculty members at Harvard University voted in recent days to cap the number of top grades they are permitted to award to undergraduate students, in an attempt to reduce grade inflation at one of America’s most prestigious colleges.

The new policy will limit A’s to 20 percent of the letter grades awarded in a course, with an allowance for as many as four additional A’s. Faculty voted on the proposal this month, and the results were announced Wednesday.

In a course with 100 students, for example, a professor would be permitted to award up to 24 A’s. There is no limit on grades of A-minus or lower, and the cap applies only to undergraduates.

The vote was 458 in favor, 201 against.

“This is a consequential vote,” Amanda Claybaugh, the dean of undergraduate education, said in a statement. “It will, I believe, strengthen the academic culture of Harvard; it will also, I hope, encourage other institutions to confront similar questions with the same level of rigor and courage.”

Grades at Harvard have been creeping upward for decades. In the 2024-25 school year, about two-thirds of undergraduate letter grades were A’s, a distinction that is supposed to be reserved for extraordinary work, according to the student handbook.

A little over a decade earlier, in 2012-13, just 35 percent of Harvard letter grades were A’s.

Grade inflation is a national problem that experts say reduces the value of grades. If most students get an A, grades become less valuable to employers, graduate school admissions officers and the students themselves as measures of their subject mastery.

In a report on grade inflation last fall, Harvard’s Office of Undergraduate Education urged faculty to be tougher graders. The school has been debating the plan to cap A’s since February.

It becomes effective in the 2027 academic year. The policy will be reviewed after three years, though it would take a new round of faculty legislation to change it.

Steven Pinker, a Harvard psychology professor who has been outspoken about the problem of grade inflation, cheered the results.

“Grade inflation forced a race to the bottom in which any professors who held the line with challenging material and standards would see their enrollments plummet,” Dr. Pinker said in an email. “It turned universities into national laughingstocks.”

Even more could be done, he suggested, such as capping the number of A-minus grades, “but this is a good start.”

Ray Fair, a Yale University economics professor who has studied grade inflation, said the Harvard cap on A’s appeared to be a step in the right direction that could have broad-reaching effects beyond Harvard’s campus.

“Harvard could be the key in all of this,” he said. “If they move it could bring other schools around.”

But the cap is unpopular with students, according to Hyunsoo Lee, a Harvard sophomore and academic officer for Harvard student government. In a survey this year, about 94 percent of roughly 800 student respondents opposed or leaned against the cap.

Many cited concerns about increased competition with classmates, which they fear will decrease collaboration, Mr. Lee said. “It incentivizes people to be selfish. We’re surrounded by the best students in the world, and we learn from each other.”

Some students also believe that competing for a limited number of top grades will increase student stress and harm mental health, he said, and will make students more reluctant to experiment and take classes in unfamiliar subjects.