Here's the Toll That Student Debt Can Take on Retirement

Student debt levels have have mushroomed, and Americans have saved little for retirement. The relationship between those two things is not obvious. So just how does having a big slug of student debt actually hurt the ability to prepare for a comfortable retirement?

To find out, Alicia Munnell, director of the Center for Retirement Research at Boston College (CRR), and her colleagues tweaked a measure developed by CRR to quantify America's retirement prospects. Their National Retirement Risk Index (NRRI) uses data from the Federal Reserve's Survey of Consumer Finances to compare how much income people are on track to replace in retirement with how much income they will need to maintain their standard of living.

The index shows that 52 percent of Americans are at risk of a shortfall in retirement, based on data that includes an average student debt load of $18,000. If you raise that debt burden to $31,000—the 2013 average for recent college students—and increase the universe of people with student loans to mirror the current situation, the outlook looks grimmer.