The German Leisure Monitor for 2014 shows one in ten people in the country work a second job at least once a week, while 20 percent work an extra job at least once a month.
Working a second job is now a more popular way to spend "leisure time" than eating out, visiting the cinema or going to the gym, said Ulrich Reinhardt from the Foundation of Future Studies which conducted the survey.
Second jobs range from so called "minijobs" such as bar work or waiting in restaurants to working on the black market.
Reinhardt said money worries were increasingly the reason behind the rise. "There is a need to cope better with the costs of everyday life," he said. He believes the numbers working a second job will continue to rise.
In 2007, just seven percent of people classified as low earners earned extra money once a week. In the 2014 study that rose to 12 percent.
At the same time, 34 percent of higher earners are willing to earn less in return for more leisure time, according to the study.
"Leisure is enjoyed less and less," Reinhardt said.
Work not paying?
Despite the healthy German economy, real wages have been falling. In 2013 they declined by 0.2 percent ending a rise from 2010 to 2013.
But the long-term trend is one of wage decline or stagnation. The German Institute for Economic Research (DIW) found in a 2009 report that real wages in Germany had hardly risen since the start of the 1990s and actually fell from 2004 to 2008.
The report said: "This is a unique development in Germany - never before has a period of rather strong economic growth been accompanied by a decline in net real wages over a period of several years.
"The key reason for this decline is not higher taxes and social-insurance contributions, as many would hold, but rather extremely slow wage growth, both in absolute terms and from an international perspective."
But what do those taking on second jobs need to know?
Advice site experto.de urges anyone doing second jobs, particularly freelance work, to familiarize themselves with the following German terms:
Honorar: Fees - these need to be agreed on and put in writing before you start any work
Mehrwertsteuer - sales tax, or value added tax should be charged by freelancers on top of their basic fee. MwSt is either charged at 19 percent or seven percent.
Rechnungsstellung - invoice - this should be sent to the employer and a copy kept for the freelancer's records.
Tell the boss?
It is ultimately your decision as an employee to take on a second job. You are free to do what you like in your free time, but you should inform your boss and there are occasions where your boss in your main job can try to stop you.
Your boss can put in an objection if you work for a rival company, if the hours at your second job push you over the legal limit of 60 hours per week, or if your extra job, taking on night shifts for example, affects your performance in your main job.
The German Leisure Monitor is based on a survey of 4,000 Germans aged 14 and over. This year's full study will be released on Wednesday.
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