In 2017 the Roman Catholic Church lost 269,000 members in Germany, the Protestant Church (EKD) lost as many as 394,000. The group of nondenominational people grew by 499,000 persons, the group of denominational Muslims by 105,000. This is shown in an overview of the Forschungsgruppe Weltanschauungen in Deutschland (fowid - Research Group on Worldviews in Germany), which was recently published on its website.​

According to fowid, nondenominational groups accounted for the largest proportion of the population in Germany in 2017 (37 percent). Catholics (28 percent), Protestants (26 percent), denominational Muslims (5 percent) and members of other religious communities (4 percent) rank far behind.

Overall the long-term trends for the two major church associations continued. Their share of the population has fallen from 56 percent (2015) to 55 percent (2016) and 54 percent (2017). If these trends are maintained or even increased (such as the death surplus among the EKD members), Catholics and Protestants are expected to fall below the threshold of 50 percent of the population in Germany in 2022/2023.

In his analysis fowid director Carsten Frerk pointed out the considerable difficulties associated with the correct classification of religious affiliations: "On one side overexact figures, on the other side outdated estimates, resulting in considerable 'residuals', whose proportions are then converted to an estimated population. We have to accept that, because there is no more precise way". The calculation of the number of "denominational Muslims", which should be distinguished from the group of "areligious cultural Muslims", proves to be particularly difficult. After reviewing various studies, the research group assumes that at least 20 percent of the people labelled as "Muslims" in Germany belong to the non-religious group of "cultural Muslims".

The complete fowid analysis can be found here (German language):

https://fowid.de/meldung/religionszugehoerigkeiten-deutschland-2017