He froze until 2028 a threshold at which employers start to pay social security contributions, which will cost companies more.
Public spending would grow more slowly than the economy but rise in overall terms, he said.
It now expects gross domestic product to contract by 1.4% next year compared with its projection in March for growth of 1.8%.
The OBR forecasts GDP growth of 1.3% in 2024 and 2.6% in 2025, compared with previous forecasts of 2.1% and 1.8% respectively.
Thursday's forecasts by the OBR showed that target would be met in the 2027/28 financial year.