Even women leaving university will earn less than men, even if they have studied the same subject, said the Equality and Human Rights Commission (EHRC).
Female graduates take home between £15,000 and just under £24,000, while their male counterparts are more likely to be on starting salaries of more than £24,000, said the commission.
The pay gap is biggest in the legal profession, with women starting on an annual salary of £20,000, around £8,000 less than men, research found.
Women are also under-represented in good-quality apprenticeships, but make up most of the workforce in low-pay sectors.
Laura Carstensen, an EHRC commissioner, said: “In today’s world women should not face these kinds of injustices, especially when data shows time after time girls and women are outperforming males at every stage in education.
“45 years after the Equal Pay Act was brought in to herald an end to gender pay inequality, our research provides clear evidence that the old economic and societal barriers are still prevalent for working women and overshadowing the prospects of our girls and young women yet to enter the workplace.
“As we enter a new year, we need to drive forward change and ensure women finally experience the fair treatment they deserve.
“We cannot continue to accept that a woman embarking upon her working life can expect to be paid less because of her sex.
“This unfairness won’t damage her alone but also those dependent on her and ultimately the enterprises and economy of this country which will fail to harness and reward all of our best talent.”
Research by the commission found that women were over-represented in part-time work or on zero-hours contracts and under-represented in senior company posts.
Women also continued to face pregnancy discrimination, including unfair dismissal, negative comments and verbal harassment, said the report.
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