Despite advances in medical technology and genetic research, overall increases in life expectancy are slowing down in countries with the longest-living populations, and scientists don’t expect much further growth, a new study finds.

According to the lead author, S. Jay Olshansky of the University of Illinois-Chicago, there appears to be a limit to human longevity. “We have to recognize there’s a limit,” he told the Associated Press, suggesting the need to reassess retirement planning and financial needs for the elderly.

The study, published in the journal Nature Aging, examined life expectancy data from 1990 to 2019, focusing on eight countries known for their longevity — Australia, France, Hong Kong, Italy, Japan, South Korea, Spain, and Switzerland. Despite its lower ranking — 40th — America was included in the analysis due to its past optimistic projections for life expectancy.

“We’re squeezing less and less life out of these life-extending technologies. And the reason is, aging gets in the way,” Mr. Olshansky said. While living to 100 may seem increasingly common, as illustrated by President Carter reaching the milestone, the study suggests that most countries will see only a small percentage of their population becoming centenarians.

In 2019, more than 2 percent of Americans reached 100, compared with approximately 5 percent in Japan and 9 percent in Hong Kong.

Analysts predict growth in the number of centenarians due to population growth, yet Mr. Olshansky estimates that fewer than 15 percent of women and 5 percent of men will achieve this age in most countries.