Nearly half of single parents have had to borrow money to pay for childcare, according to a report.
The campaign group Gingerbread said the increasing cost of childcare proved the idea that work was the best route out of poverty was "far from reality" for many single parent families.
A new report said a poll of 1,700 single parents showed that half have had to borrow money from friends, family or banks to fund childcare in the last two years.
The charity is calling on the Government to raise the maximum amount of childcare costs that low-income families can claim, to reflect the actual costs they face.
It said a decade-old cap meant that, even with the extra help to be rolled out under Universal Credit which increased support from 70% to 85% of costs, for many single parents there is no financial benefit working longer.
Gingerbread chief executive Fiona Weir said: "Childcare costs are putting single parent families under severe financial strain.
"Childcare just isn't affordable for many and it is very worrying that single parents are having to turn to friends and family, banks and credit cards to try and cover costs.
"We welcome Government plans to increase the amount of support available, but the cap on costs means too many single parents will see little benefit.
"The Government must honour its commitment to make work pay and swiftly bring in extra financial support - parents can't afford to wait any longer."
A recent survey by the Family and Childcare Trust found childcare costs have increased by almost a third in the last five years.
On average in England, Scotland and Wales sending a child to nursery for 25 hours a week costs £115.45.
That is 5.1% more than last year and 32.8% more than in 2010.
Children aged between nine months and two years could get 15 hours of free childcare if the Liberal Democrats are still in government after the General Election in May.
The issue of childcare costs is likely to feature highly in the run up to the election, with politicians keen to use today's report to score political points.
Last month Nick Clegg pledged a major expansion of free childcare for toddlers, which could save an average family where both parents work £2,670 a year.