Three-quarters of divorced or separated mums will be unable to afford to pay for basics such as food and heating when they retire.
This is because of the financial and career disadvantages mothers face, which have an enduring impact on later life, according to a new study from Scottish Widows.
Many mothers do not earn as much as men and cannot save as much for retirement as they are more likely to take career breaks to raise their children.
Single mothers are hit harder by these financial disadvantages as they are unable to share the burden of day-to-day costs and childcare with a husband.
More than half (51%) struggle to find jobs in the first place while 46% reduced their hours in order to manage childcare.
The research also indicated that two-thirds of single women generally are not on track for a minimum lifestyle (which covers the basics with some discretionary income) in retirement.
This is much higher than women who are married, in a civil partnership or cohabiting – of whom only 23% are unlikely to be able to afford the most basic lifestyle.
It is also higher than single men – 54% of whom are not on track – according to the report.
Jackie Leiper, the managing director of Scottish Widows, said: “Despite how familiar we all are with the gender pension gap issue, the long-term impact on the day-to-day reality for women when they retire is less talked about.
“Understandably, single women affected by the motherhood penalty and the cost of solo parenting may be more focused on how to support their family today, but this report shows the struggle they could face by the time they become grandmothers.
“We must recognise the amount of childcare responsibility that falls on single mothers and their huge contribution to society, which means they should be protected by policies to limit the impact it has on their careers and pensions.
“The Government needs to prioritise affordable childcare to improve the retirement prospects for all mothers and single mothers in particular.”
The report also found that half of fathers said they share childcare equally with their wives though less than a third (31%) of mothers believe this to be true.
And 37% of mothers said they had left jobs to look after their children, as had 18% of fathers.
Alesha De-Freitas, the head of policy, advocacy and research at the Fawcett Society, said: “We need urgent childcare reform that prioritises accessibility and affordability for everyone, and this needs to work in tandem with an economy that delivers high-quality flexible work.”
The report used YouGov research among more than 5,000 people across the UK in March and April this year.
It also used the Pension and Lifetime Savings Association’s retirement living standards to calculate the quality of lifestyle that people could achieve when they stop working.
“A key driver of the gender pension gap continues to be the gender pay gap, which, although has seen significant strides from employers to fix; is evidently causing a knock-on effect on pension wealth for women.
“And while some women may contribute the same proportion of their salary to their pension as men in their lifetime, other important factors are at play. Women are still disadvantaged if they have children or have other family caring responsibilities.”
A Government spokesman added: “The success of automatic enrolment has transformed the UK pensions landscape and brought millions of women into pension saving for the very first time, and our expansion of free childcare in England means working families could save an average of £6,500 per child per year, meaning parents who are ready to return to work will benefit from the single biggest investment in childcare ever.
