Two-thirds of professional women return to work after a career break in lower-paid or lower-skilled roles, or working fewer hours than they'd like.
Of those, three in five - so around 249,000 - are likely to enter lower-skilled roles on return to work. The research pointed out this then has a knock-on impact on earnings: the downgrading is associated with an immediate 12-32 per cent reduction in hourly earnings, depending on whether the woman remains with the same employer.
Then there are another 29,000 women returning to part-time work who would prefer to work longer hours, but can't due to a lack of flexible roles out there. In 2015, a Timewise study found that six per cent of advertised roles with a salary of over £20,000 were available on a flexible basis and that shrunk to two per cent for roles with a salary of over £100,000.
In total, two-thirds of women, or around 278,000 women could be working below their potential when they return to work.
Tackling this "occupational downgrade" could then result in economic and business gains for professional women working at their full potential, increasing combined annual earnings by £637m.
Boosting the number of hours for part-time working women could contribute an additional 14,000 full-time employees to the UK workforce annually. That would also bump up the earnings of this group of women by £423m.
Read more: Mums could boost London economy by £16bn
Overall the research estimates that returning professionals lose out on £1.3bn of earnings annually from the career break penalty, equivalent to £4,000 each per woman.
Laura Hinton, executive board member and head of people at PwC, said: "The business and economic arguments for getting more women back into high quality work following a career break are compelling.
"Our research shows the UK economy could see a £1.7bn boost, women will get higher earnings and businesses will benefit from a stronger pipeline of female leaders and more diverse teams. Many women want to return, it is the system that needs to change."