The indicator was tempered this month, reduced by problems in the manufacturing sector regarding supply and raw materials bottlenecks.
Ifo placed the balance in this regard at 98.8 percent, after 99.6 percent last month.
German businesspeople also worsened the evolution of the current situation by one point, from 101.4 in August to 100.4 this September. Ifo President Clemens Fuest stated that companies were less satisfied with their current level of business.
He added that they were also more skeptical about the next few months. Problems in the supply of raw materials and intermediate goods are weighing down on German economy, he said.
The business atmosphere in the services sector improved, from 17.8 points in August to 19.1 in September.
The construction sector in turn experienced even greater growth, when it reached 10.9 points, from 8.1 in August.