CHICAGO — Consumer’s confidence about the U.S. economy fell unexpectedly in October as job prospects remained bleak, a private research group said Tuesday, fueling speculation that an already gloomy holiday shopping forecast could worsen.

The Consumer Confidence Index, released by The Conference Board, sank unexpectedly to 47.7 in October — its second-lowest reading since May.

Forecasters predicted a higher reading of 53.1.

A reading above 90 means the economy is on solid footing. Above 100 signals strong growth.

The index has seesawed since reaching a historic low of 25.3 in February and climbed to 53.4 in September.

Shoppers have a grim outlook for the future, The Conference Board said, expecting a worsening business climate, fewer jobs and lower salaries. That’s particularly bad news for retailers who depend on the holiday shopping season for a hefty share of their annual revenue.

“Consumers also remain quite pessimistic about their future earnings, a sentiment that will likely constrain spending during the holidays,” said Lynn Franco, director of The Conference Board’s Consumer Research Center.

Economists expect holiday sales to be at best flat from a year ago, which saw the biggest declines since at least 1967 when the Commerce Department started collecting the data.

The Consumer Confidence Index survey, which was sent to 5,000 households, had a cutoff date of Oct. 21.