Women managers are effectively working for free for 57 days a year because of a gender pay gap, according to a new study.

A survey of 72,000 managers found that women in equivalent full-time jobs earned 22% less than men.

The difference means they are working for an hour and 40 minutes without pay every working day, said the report by the Chartered Management Institute (CMI) and wage analysts XpertHR.

The gender pay gap for professional roles averages £8,500 a year, rising to almost £15,000 for senior staff, it was discovered.

The gap gets wider as women grow older, ranging from 6% for women aged 26-35, to 38% for the over 60s, said the report.

The research also showed there were fewer older women in executive positions.

Women outnumber men in junior management jobs, but fewer than one in four are on company boards, just short of a 25% target set by a Lord Davies-led study.

Ann Francke, chief executive of the CMI, said: “Working for free two hours a day is unacceptable. While some progress is being made, it’s clear from our research that Lord Davies is right to target the executive pipeline.

“Having more women in senior executive roles will pave the way for others and ensure they’re paid the same as their male colleagues at every stage of their careers.”

Mark Crail of XpertHR, added: “An entire generation has now worked its way through from school leaver to retirement since the first equal pay legislation came into effect in 1970, yet the gender pay gap persists, and many employers still prefer not to know just how bad it is in their organisation rather than getting to grips with the data and doing something about it.

“HR and reward specialists in larger companies have a special responsibility to get this firmly on to the senior management agenda and to develop the plans needed to close the gap.”

The report said pay transparency was a “powerful driver” for closing the gender gap.