Americans Are Suddenly Upbeat About Economy. Sentiment Just Logged Its Biggest Jump in Decades.

Americans are rapidly becoming much more upbeat about the economy.

Consumer sentiment leapt 13% in the first half of January from December, the University of Michigan said Friday. That came on the heels of a sharp rise in December, causing the index to surge a combined 29% from November, the biggest two-month increase since 1991. The pickup in sentiment was broad-based, spanning consumers of different age, income, education and geography.

The recovery in sentiment “is likely to provide some positive momentum for the economy,” said Joanne Hsu, the Michigan survey’s...