The figure for May fell to a record low of 48.2 - from 49.8 in April, according to the Bloomberg news agency.
The survey is based on responses between April 21 and May 4. The explanations for the gloom include expectations of higher inflation in the wake of higher fuel prices and President Donald Trump's import tariffs, which together are digging holes in household budgets.
Joanne Hsu, the head of the study at the University of Michigan, points out in a comment the costs people face when they refuel.
"Overall, consumers continue to feel burdened by cost pressures, led by rising prices at the pump."
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