Church tax is a deduction paid only by members of religious communities that levy taxes. It amounts to 9% of your wage tax (only 8% in Bavaria and Baden-Württemberg). Sounds small? With a gross salary of €4,500 and wage tax of around €600, that's €48-54 per month – so €576-648 per year.
Does leaving the church pay off financially? Purely in terms of numbers: yes, especially at higher incomes. At €6,000 gross, leaving the church saves you around €80-100 per month, or €1,000 per year. However: church tax is tax-deductible, which reduces the savings by about a third. In real terms, you save around €650-700 annually. Leaving the church happens at the registry office or local court (depending on the state) and costs a one-time fee of €0-60.
Good to know: the deduction happens automatically if the Federal Central Tax Office has you registered as a church member. After leaving, the tax obligation ends the following month. You can then, for example, donate the saved church tax directly – which is then even 100% deductible, not just a third.