It has been joked that the letters IMF stand for “it’s mostly fiscal”. The International Monetary Fund has long been a stalwart advocate of austerity as the route out of financial crisis, and every year it chastises dozens of countries for their fiscal indiscipline. Fiscal consolidation – a euphemism for cuts to government spending – is a staple of the fund’s rescue programmes. A year ago the IMF was suggesting that the US had a fiscal gap of as much as 10 per cent of gross domestic product.

All of this makes the IMF’s recently published World Economic Outlook a remarkable and important document. In its flagship publication, the IMF advocates substantially increased public infrastructure investment, and not just in the US but much of the world. It asserts that when unemployment is high, as it is in much of the industrialised world, the stimulative impact will be greater if investment is paid for by borrowing, rather than cutting other spending or raising taxes. Most notably, the IMF asserts that properly designed infrastructure investment will reduce rather than increase government debt burdens. Public infrastructure investments can pay for themselves.

Why does the IMF reach these conclusions? Consider a hypothetical investment in a new highway financed entirely with debt. Assume – counterfactually and conservatively – that the process of building the highway provides no stimulative benefit. Further assume that the investment earns only a 6 per cent real return, also a very conservative assumption given widely accepted estimates of the benefits of public investment. Then, annual tax collections adjusted for inflation would increase by 1.5 per cent of the amount invested, since the government claims about 25 cents out of every additional dollar of income. Real interest costs, that is interest costs less inflation, are below 1 per cent in the US and much of the industrialised world over horizons of up to 30 years. So infrastructure investment actually makes it possible to reduce burdens on future generations.