Munich's Religion Tax

I'm now an official German tourist. My residence permit expires on the 20th. And instead of renewing (as we're only here another four months - with a trip back to Chicago in October), our relocation services contact agreed with us that it didn't make much sense to renew. As a result, we had to "de-register" me as it's the law.

Another law I learned of today is the "religion tax." While filing for a residence permit, the form asks your "religion preference." When I questioned why that was anybody's business, I was told it's because Munich's residents pay 9-10% of their income tax to a specified religion. If that's the case, to save money, wouldn't you just say your an atheist?