This myth has been busted many times. Women do not earn less than men for the same work.
Not true. A colleague's experience in a large mining company: four engineering graduates coming off their graduate programme, three male, one female. The three males all got offered the same base pay, several thousand above what the female was offered. All in the same department, doing the same job.
Another one, this time applying for a role in a mining consultancy business: an engaged couple both applied for the same role in financial/business analysis (potential employer unaware of their relationship). She had finished two degrees, one in mining, one in finance ie highly relevant to the role. He was yet to finish his one degree (mining). Both offered the role (not at the same time), except she was offered $70k and he was offered $85k.
I don't know how prevalent this is, but it's far from being a myth.
Low level and graduate position remuneration packages are generally assigned by Human Resources, an employment sector with a high female %. Are we seriously saying the 'old boys club' heads are heading down stairs and making sure their lowest rung employees are paid marginally less, just because?
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In the end as a male or a female, you will only achieve the maximum pay by demanding it in a negotiation environment.
When I heard about my colleague's experience, the HR question came up. They don't get to decide the actual pay rate, they have pay bands. The line managers decide the pay rate within the applicable band, and that can and obviously does, vary.
In saying that, I agree with the comments to do with life choices etc. I do think leaving the workforce to have children, doing part time work etc all contribute to the pay gap, as does the general reluctance of women to be more assertive when pay reviews come up. Unfortunately that does not preclude a genuine gender pay gap from being reality in many cases though.