Women, especially those with children, are still being paid significantly less than their male counterparts, a report by the Institute for Fiscal Studies has found.
The study, funded by the charity the Joseph Rowntree Foundation, found on average women earn 18% less per hour over their lifetime than men.
The figure is an improvement on the average 28% pay gap recorded in 1993.
However, when the numbers are broken down the progress is not as encouraging as it might first seem, report author Robert Joyce told BuzzFeed News.
He said this was because the statistics were skewed by an increase in the number of women who are well educated and therefore earning more.
The pay gap between men and women who are university-educated is larger at 20%, Joyce said.
Motherhood also had a significant impact on the gender pay gap, according to the study. On average men are paid 10% more than women before the arrival of the first child, but this gap was found to increase steadily to 33% over the first 12 years of the child's life as women face fewer opportunities for pay growth.
While educated women were less likely to leave work or go part-time after the birth of a child, the greater wage gap was explained by mothers missing out on pay rises, promotions, and experience over their working life.
Women educated to GCSE level were most likely to stop working, Joyce added, though at the same time they also had the most pay parity with their male counterparts.
Jemima Olchawski, head of policy at the Fawcett Society, a charity for women's rights, said the findings showed there needed to be a "change and shift in the balance" between men and women.
"It's clear women are still earning less than men and a big driver of that is that women are more likely to take on unpaid care outside the workplace – whether that's as mothers or carers," she told BuzzFeed News.
"One thing we'd point out is just how unnecessary that is [but] only 6% of good-quality jobs are advertising as flexible or part-time."
She said "unless there is a business case not to" employers should consider making it easier for mothers to continue to work and should also incentivise men to take up more parental responsibilities and shared parental leave.
However, social stereotypes about the role of men and women were also preventing men from being supported in doing so – with one-third of men feeling they are not supported to take time off work to care for their family.
The government launched two consultations on proposals that require large companies with up to 250 employees to publish gender pay gap figures.
The new regulations won't become mandatory until 2018, and this delay has drawn criticism.
A government spokesperson told the BBC: "The gender pay gap is the lowest on record but we know we need to make more progress and faster.
"That's why we are pushing ahead with plans to force businesses to publish their gender pay and gender bonus gap – shining a light on the barriers preventing women from reaching the top."