It can cost the taxpayer over £154,000 to support a single mother over a decade, a think-tank has suggested.
Two-parent families should be supported, the think-tank says
Calculations by the Centre for Policy Studies (CPS) also suggest the average family break-up costs the taxpayer £72,000 over 10 years.
Single mothers with two children cost the government between £71,000 and £154,000, the report said.
The figure depends on whether they work or receive payments from absent fathers, it added.
The findings show how much family break-ups are being subsidised by the tax and welfare system, the CPS said.
Cambridge economics professor Bob Rowthorn, who calculated the figures for the report using Department for Work and Pensions tables, said the long-term cost of the subsidies was "unsustainable".
"It is time to switch resources towards a system that encourages and supports two-parent families to ensure their survival," he said.
'Cost of billions'
He said that a family with two young children, where two parents had average weekly incomes of £460 and £250, would pay £76,000 tax over a decade.
But if they split and carried on earning the same then, taking into account benefits paid out, they would pay £4,000 tax in real terms.
The loss to the Exchequer was £72,000 over 10 years, he added.
The cost to the government ran into billions when taking into account recent research suggesting one in three children experience parental divorce or separation, the CPS says.
Mr Rowthorn's calculations assume no change in tax or benefit levels over the 10 years.