German rent law measures rents against a derived figure, the ortsübliche Vergleichsmiete, the local comparative rent. Section 558 of the Civil Code defines it. It is formed from the usual rents agreed or changed in the last six years for housing of comparable type, size, equipment, condition and location. Towns with more than 50,000 inhabitants must publish a rent index, a Mietspiegel. A qualified rent index must be prepared according to recognized scientific principles. In areas with a tight housing market, the rent for a new lease may exceed the local comparative rent by no more than 10 percent. This Mietpreisbremse, the rent brake, may apply until the end of 2029. A landlord who exploits a shortage to charge more than 20 percent above the comparative rent commits an administrative offense. The fine can reach 50,000 euros.