The deposit can serve as security for the landlord regarding claims against the tenant arising from the rent contract and must be agreed upon contractually.
Generally, the deposit including interest must be refunded to the tenant immediately, provided the tenant has not caused any damage to the rented object and is not in arrears with the rent. “Immediately” means that the landlord has a deadline of a couple of days to determine possibly existing claims against the tenant. It is not admissible to keep the deposit back until the operating costs or heating costs for the current year become due.