For most of the past 10 years, corporate debt has been little more than an afterthought for many investors. With interest rates low, the economy strong, and relatively easy lending standards, the thinking went that borrowing to buyback shares or finance acquisitions was a low-risk strategy. But the next five years could severely test that Pollyanna view.

As shown in the chart, roughly $3.3 trillion—48% of all current outstanding commercial debt—will come due by 2023. The sheer volume would be challenging for the market to digest in the best of scenarios, let alone this late in an economic expansion. Adding to our sense of caution are early signs that lending standards have begun to tighten for commercial and industrial borrowers. As banks become more stringent, borrowers could find themselves paying higher rates just to secure the capital they need to retire outstanding obligations.