This is simple – and yet, probably too complex for your typical wingnut relative! Brad DeLong:
The US government can currently borrow for 30 years at a real (inflation-adjusted) interest rate of 1% per year. Suppose that the US government were to borrow an extra $500 billion over the next two years and spend it on infrastructure – even unproductively, on projects for which the social rate of return is a measly 25% per year. Suppose that – as seems to be the case – the simple Keynesian government-expenditure multiplier on this spending is only two.
In that case, the $500 billion of extra federal infrastructure spending over the next two years would produce $1 trillion of extra output of goods and services, generate approximately seven million person-years of extra employment, and push down the unemployment rate by two percentage points in each of those years. And, with tighter labor-force attachment on the part of those who have jobs, the unemployment rate thereafter would likely be about 0.1 percentage points lower in the indefinite future.
The impressive gains don’t stop there. Better infrastructure would mean an extra $20 billion a year of income and social welfare. A lower unemployment rate into the future would mean another $20 billion a year in higher production. And half of the extra $1 trillion of goods and services would show up as consumption goods and services for American households.
In sum, on the benefits side of the equation: more jobs now, $500 billion of additional consumption of goods and services over the next two years, and then a $40 billion a year flow of higher incomes and production each year thereafter. So, what are the likely costs of an extra $500 billion in infrastructure spending over the next two years?
For starters, the $500 billion of extra government spending would likely be offset by $300 billion of increased tax collections from higher economic activity. So the net result would be a $200 billion increase in the national debt. American taxpayers would then have to pay $2 billion a year in real interest on that extra national debt over the next 30 years, and then pay off or roll over the entire $200 billion.