U.S. consumer sentiment stayed elevated throughout December, with upper-income households contributing most of the gains during the month, according to new monthly data from the University of Michigan's Surveys of Consumers.

The final consumer sentiment index came in at 99.3, up from 96.8 in November. The latest print was marginally higher than the preliminary reading for December as well as the consensus estimate of economists polled by Econoday, both of which put the figure at 99.2.

The current economic conditions index rose month over month to 115.5 from 111.6, while the consumer expectations index improved to 88.9 from 87.3.

Surveys of Consumers Chief Economist Richard Curtin noted that upper-income households contributed the most to the improvement of consumer sentiment in December, with optimism among households at the top-third of the income distribution gaining 7.5%, while those at the bottom two-thirds gained only 0.8%.

He also said that the two best extended periods of optimism in the history of the consumer polls both occurred around an impeachment year. The four years from 1997 to 2000, when the consumer sentiment index averaged 105.3, happened around the time of impeachment proceedings against former President Bill Clinton. Meanwhile, the period from 2017 to 2019, when consumer sentiment averaged 97.0, includes the impeachment of President Donald Trump.

"The impeachment hearing had a barely noticeable impact on economic expectations, as it was mentioned by just 2% of all consumers in the December survey," Curtin said.

Households surveyed had low inflation expectations in December, with consumers projecting year-ahead annual inflation to be at 2.3%. Average yearly inflation in the next five years was expected to be at 2.2%, according to the survey.