And smartphone mobile data speeds are even worse.
According to the study published Wednesday, the BNetzA studied Germany's leading service providers for a year between October 2016 and September 2017.
The results were somewhat surprising. For a staggering 29 percent of German users, internet speeds were less than half of that which companies promised in their contracts. And almost no one, even those paying a premium for the best service, reached the "maximum" speeds vendors promised.
The numbers were even more unimpressive for smartphones. Only 18.6 percent of users reached even half the contractually agreed speed and bandwidth for mobile data. This means that the situation is only getting worse — in 2015, the number was 27.6 percent.
The study showed that a mere 1.6 percent of German smartphone users can reach the promised internet speeds on their devices.
Providers do not seem concerned how bad their service is for the German economy, as slow internet speeds are problematic for businesses fighting international competition.
Despite the poor performance figures, the BNetzA is not in a position to sanction or fine providers.
Industry association Bitkom responded to the report by saying that "technical reasons" sometimes hindered companies from providing promised speeds.