German law /Statute of limitations to claim rent and utilities

For utilities, the rental contract specifies how the cost is calculated (What does your contract say?):
- If nothing is specified, no costs can be charged (meaning all is included in the base rent).
- Items can be charged by usage (common for water if there is a meter), as a fixed sum per month (common for insurance, etc.), as a sum per person (common for garbage fees) or by apartment size (in sqm).
- Heating energy must, according to the regulations, be charged by use in almost all cases.
- The landlord must prepare a detailed utility bill yearly and has 12 months after the year ends to prepare the calculation. If he doesn't, within this period, he cannot claim any money (and under some circumstances must even return the pre-payments, if any were paid).
- The tenant can claim back any overpayment within the last three years.

About rent increases:
- Most rental contract agreements about automatic rent increases are invalid. Get yours checked by a lawyer or tenants' association!
- If it is valid, the landlord can claim the missing payments from the last three years.

For all disputes between tenants and landlords (if they cannot be resolved by talking to each other), consulting a tenants' association ("Mieterverein") should be the first step. You have to become a member, though.