Women in their twenties and thirties aren't able to put enough money aside for their retirement, because they're bearing the full cost of childcare, according to a new report by the Fawcett Society.
The gender equality charity's study also found that women rely on men to sort out their pensions because they "lack confidence" about their finances.
It warned that many women faced poverty in old age because they didn't realise the drastic long-term impact of failing to save up earlier in life.
The research, published on Wednesday, was carried out by academics from Sheffield University who conducted qualitative interviews with 30 women from across the UK and a focus group with 12 women in Sheffield. All the participants were aged 25 to 39 and earned between £24,000 and £40,000 a year.
It aims to cast light on the reasons why women save less for retirement than men.
Only 52% of women aged 30 and over are saving enough, compared to 60% of men, according to pensions firm Scottish Widows. Of this group, a quarter of women are saving nothing, compared to just 15% of men.
The Fawcett Society study said that while many women wanted to save for a pension when they started a family, they were hamstrung by the "triple cost" of taking time off work, reducing hours when back at work, and the ongoing costs of childcare.
"Women consistently described childcare as a cost paid from their incomes rather than as shared with their partners," the report said. "This significantly limited their disposable income and ability to save for retirement."
Pensions were viewed by the women interviewed as "a cost without reward" and likened to "the experience of paying a tax".
Many pointed to their father or partner as someone who knew more about their own pension. "Many of the women did not feel confident making decisions with numbers and perceived the men they sought advice from to be better equipped to engage in these issues," the report said.
The study recommended that employers should encourage staff going on parental leave to keep saving into a pension pot while they're off work.
It also said the partner who stays in work, usually a man, should top up their partner's pension contribution during parental leave to make sure the cost is shared between the couple.
Fawcett Society chief executive Sam Smethers said: "The gender pay gap becomes a pensions gap in retirement. In particular women are taking a big hit on their pensions when they have children, but are not aware of the impact this will have on them in the long term."
She added: “Worryingly there are some really strong gendered attitudes being displayed here, with many of the women we interviewed not confident when faced with decisions about pensions and often asking men for advice.
"The interviews revealed that many of those in relationships were relying more on their partner for security in retirement that they realised. The 1950s male breadwinner model is alive and well in 2016."