The Restriction When Moving Out: New Tenant Clause
You want to move out earlier, have a great new job in another city or are moving in with your partner. But the contract puts obstacles in your way.
What the contract says
"Early return is only possible at the end of a month. Notification to the landlord must be made in writing at least 30 days before the planned return."
A clear violation of your freedom. This clause attempts to inadmissibly restrict your right to early return.
According to Art. 264 CO (Swiss Code of Obligations), you can be released from liability at any time, i.e. on any day, provided you propose a reasonable and solvent replacement tenant who accepts the contract under the same conditions. You are bound neither to the end of the month nor to a 30-day lead time.
Conclusion
The landlord can write it that way in the contract, but the law takes precedence. You are allowed to leave earlier.