A study predicts that Germany's two main Christian churches will lose millions of members over the coming decades and have to tighten their financial belts as a result.

The study released Thursday by the Catholic German Bishops Conference and the Evangelical Church in Germany predicts that their combined membership will drop from about 45 million now to 34.8 million by 2035 and 22.7 million by 2060.

Researchers at the University of Freiburg who conducted the study said the reasons for the decline include more church members dying than children being baptized, and adults deciding to formally leave the faith.

Members of the Catholic and Protestant churches in Germany pay up to 9% of their taxable income to the church, generating billions of euros each year for the two institutions.