It had previously been placed at 23.1% (£8,964), when based on the basic salary of managers.
The research also highlighted 66% of junior management roles were filled by women compared to 34% by men.
“Too many businesses are like glass pyramids, with women holding the majority of lower-paid junior roles and far fewer reaching the top,” CMI chief executive Ann Francke said.
“We now see those extra perks of senior management roles are creating a gender pay gap wider than previously understood.”
The pay gap is more noticeable in senior roles, with women earning an average of £141,529 compared to the average of £175,673 earned by men.
“The picture is [worse] at the top, with male CEOs cashing-in bonuses six times larger than female counterparts,” Francke said.
Bonus payments were said to worsen the problem, with the gender bonus gap across all managers being 46.9%.
This is elevated at C-suite level, where female CEOs earn an average of £14,945 in bonuses compared to male CEOs who earn an average of £89,230.
While there were suggestions of increased salaries and bonuses for men and women, the benefits were disproportionately given to men. This was especially common among directors, where men saw a 5.8% increase in pay and bonuses compared to 3.7% for women.
The research was based on new reporting regulations which required companies to report on the pay of men and women in their company, including salaries, bonuses, and perks such as car allowances.
Despite the regulations coming into force in April, only 72 out of 7,850 UK companies fulfilled their obligations.
“Our data shows we need the government’s gender pay gap reporting regulations more than ever before. Yet, less than 1% of companies have reported so far,” Francke said.
XpertHR Content Director Mark Crail said the results not only proved the existence of the gender pay gap, but also allowed it to be quantified.
“Some people have tried to explain the gender pay gap away as being the result of different working hours or individual choices,” he said.
“But when the analysis is based on the pay of more than 100,000 individuals in well over 400 organisations, it is clear that the pay gap is a very real fact of life for UK managers.”
In February, the PwC’s Women in Work Index predicted it would take another 24 years to close the pay gap between male and female earnings in the UK.