The gender pay gap is something all too many female employees are familiar with.
Now, research suggests women in wealthy households earn a staggering 25 per cent less than men.
This is much higher than the four per cent difference in earnings in poorer homes, the findings revealed.
And experts warned its partly because women are still expected to take on unpaid care work to look after children and the elderly.
The gender pay gap refers to the difference between average earnings of men and women in the workforce – not just unequal pay for the same work.
The researchers, from City St George's at the University of London, analysed 40 years of retrospective work–history data in the UK.
They discovered in higher–earning households, men earned an average of £29.27 per hour while women earned £21.94 per hour – a difference of 25 per cent.
Meanwhile in lower–earning households, the average hourly earnings are £8.22 for men and £7.90 for women – a difference of four per cent.
The research found that pay inequality is less of an issue in poorer households as both men and women in the UK earn such low wages.
In addition to the differences by class, the study found that women spending less time in traditional full–time work accounts for nearly a third of the gender pay gap on average.
On average, women are more likely than men to accept reduced–hour jobs, part–time work, poorly paid work, or to spend time out of the workforce entirely.
Women do so to take on unpaid caring labour, such as looking after children and relatives, which negatively impacts their earnings in both the immediate term and over time.
Dr Vanessa Gash, lead author of the study, said: 'Both gender and class need to be looked at by policymakers to reduce the gender pay gap.
'Efforts to close the gender pay gap need to be more strongly tied to an agenda of good quality employment for all.
'Calls for pay equity, which focus on the lack of women in high–powered positions, risk alienating those in households where both partners earn similarly low wages.
'Key to the problem is the age–old question of who is doing most of the unpaid care work in the home, which our research confirms continues to be women.'
The findings, published in the Cambridge Journal of Economics, revealed men had an average work history of less than three weeks of unpaid care work in their entire lifetimes.
Women, meanwhile, had an average of more than two years of unpaid care work.
Sex discrimination is another major driver of the gender pay gap, the authors said. They concluded that women face disproportionately high penalties simply for being female.
Removing this societal penalty for being a woman could contribute to a 43 per cent increase in women's wages, they added.
The paper was co–authored by researchers at the University of Manchester and the University of Salzburg.
