Most US male workers experience the bulk of wage growth by 35, while high earners continue to see pay increases after that, widening wage disparity with age, research by an economist at the Federal Reserve Bank of St. Louis showed.

This is according to a new blog post by Serdar Ozkan, an economic policy adviser who sourced data from Internal Revenue Service tax forms to track wages for men between the ages of 25 to 55 and then ranked the workers into 50 equally sized groups. The research focused on men because of the difficulties in getting uninterrupted earnings histories for women.

Among the highest-earning group, incomes surged by roughly 435% between ages 25 and 35. These workers likely entered the labor market later in life and with more education. Those in the middle experienced a 65% uptick, and people at the bottom only realized a 16% gain.

The income gap at age 25 was around 3.25 times between the highest and lowest 2% of earners. The gap widened by age 35, with the top workers earning 15.3 times as much as the bottom workers.

Between 35 and 45, median-income males saw wages increase by 15%, sharply slower than the previous decade’s 65% jump, while workers at the top saw wages increase another 150%. Therefore, the earnings gap between the highest and lowest paid jumped to 33.1 times.

Between ages 45 and 55, bottom earners experienced a decline of 14% in their average earnings, while those at the top continued to see wage growth. This further increased income inequality. By age 55, the top earners made 47.8 more than bottom earning men.

This article was provided by Bloomberg News.