UBS set out to answer a key question about US consumer debt - and their findings are worrying

Why are US consumers defaulting?

That's the question in a big note out from Matthew Mish and Stephen Caprio at UBS, which uses evidence from the bank's proprietary US Housing Intentions Survey to try and get at an answer.

According to their research, 65%, 36% and 22% of lower, middle, and higher income cohorts are "stressed" in finance speak. That means that their income falls below or just below their expenses.

In addition, lower and middle income groups are relying more and more on their credit cards, with these groups reporting a higher utilization of credit card debt.

That comes at a time when credit cards are being handed out at a historic rate, and several Wall Streeters are worried about the auto loan market.

"These responses would appear consistent with our prior thesis that easy lending standards, rising consumer inequality and too much liquidity have resulted in too much capital chasing too few creditworthy borrowers," the note said.

Let's dive into the numbers: