No, if you don't make any profit on the rent, the income is not liable to tax. If, however, you charge a higher rent or provide substantial services (e.g. cleaning, breakfast, etc.) for a fee, you must declare the earnings as additional income on your tax return.
If your sub-tenant is registered with the municipality, you do not have to pay a tourist tax, overnight stay fee, guest tax, etc. The same applies if your sub-tenant has registered with the municipality as a weekly or short-term resident. These regulations vary by municipality, but in principle are generally the same.
The regulations concerning an obligation to register a sub-tenant vary from canton to canton. In many cantons, you are obliged to inform the residents' registration office when your sub-tenant moves in or out (the 'Drittmeldepflicht' or third-party notification obligation – see graphic). Even if you are not obliged to do so, it is prudent to recommend that your sub-tenant register with the municipality. The municipality will inform your sub-tenant whether or not they need to register personally.
We also recommend registering correctly with regard to the visitor's tax (see above).
In the cantons of Zurich and Aargau you can register your subtenant online: Online registration
If you are leaving Switzerland for less than 3 months, you usually do not have to inform the local authority. However, if you are travelling for a longer period, you should ideally contact your municipality in advance to clarify whether you need to officially de-register. The notification requirements vary from canton to canton. However, the decisive factor for the obligation to register is usually whether you intend to return to Switzerland after a temporary stay abroad or whether you will move the centre of your life abroad.
We are happy to recommend the brochures and information pages of the Swiss Confederation. Unfortunately, most of them are only available in the Swiss national languages.
If you deregister at the municipality, remember to register with the responsible Swiss mission abroad (embassy or consulate): Online desk for Swiss nationals residing abroad
You can find special notification requirements for those liable for military service here (in German): Gesuch für Auslandurlaub
No responsibility is taken for the correctness of this information.