The 2014 National Management Survey is based on the pay data of almost 70,000 employees in executive positions, collected in conjunction with XpertHR. It suggests the pay gap for managers increases dramatically with age.
For those aged between 26- and 35-years-old it stands at 8%, and jumps to 23% for the age group between 36 and 45. At 46, the gap of 34% persists until retirement age (65), when it increases very slightly to 35%.
Bonus payments are also significantly higher for male executives, who receive an annual average of £53,010 compared to £41,596 for women.
The pay discrepancy means female managers would have to work on average 14 years more than their male colleagues to earn as much over a typical working life.
CMI chief executive Ann Francke called on companies to pay women and men "on the basis of their performance".
"Lower levels of pay for women managers cannot be justified, yet our extensive data shows the pay gap persists, with many women hit by a mid-life pay crisis," she said. "We have to stamp out cultures that excuse this as the result of time out for motherhood and tackle gender bias in pay policies that put too much emphasis on time served.”
Shadow minister for women and equality Gloria De Piero added the figures paint a "depressing picture" for women in the UK.
"We should be closing the pay gap for women at all stages of their working lives but instead we see pay inequality worsening for female managers as they progress and for working women across the country," she said.