At present, the average cost of Treasury borrowing is 2.5%. The average over the last two decades was 5.7%. Should we ramp up to the higher number, annual interest expenses would be roughly $420 billion higher in 2014 and $700 billion higher in 2020. The 10-year rise in interest expense would be $4.9 trillion higher under “normalized” rates than under the current cost of borrowing. Compare that to the $2 trillion estimate of what the current talks about long-term deficit reduction may produce, and it becomes obvious that the gains from the current deficit-reduction efforts could be wiped out by normalization in the bond market.
The second reason for concern is that official growth forecasts are much higher than what the academic consensus believes we should expect after a financial crisis. That consensus holds that economies tend to return to trend growth of about 2.5%, without ever recapturing what was lost in the downturn. But the president’s budget of February 2011 projects economic growth of 4% in 2012, 4.5% in 2013, and 4.2% in 2014. That budget also estimates that the 10-year budget cost of missing the growth estimate by just one point for one year is $750 billion. So, if we just grow at trend those three years, we will miss the president’s forecast by a cumulative 5.2 percentage points and—using the numbers provided in his budget—incur additional debt of $4 trillion. That is the equivalent of all of the 10-year savings in Congressman Paul Ryan’s budget, passed by the House in April, or in the Bowles-Simpson budget plan.