Rent increase (Mietzinserhöhung).

A rent increase must be announced on the official form approved by the canton, at least ten days before the notice period of the next termination date starts: for a flat with three months' notice, at least three months and ten days before that date. The form must state the new rent and the reason. Without the official form the increase is void (art. 269d OR).

Valid reasons

• A higher reference interest rate: up to 3% more rent per 0.25 point rise, while the rate is below 5% (art. 13 VMWG). The rate has been 1.25% since 2 September 2025 and was confirmed on 1 September 2026 (BWO). When it falls, you can ask for a reduction (art. 270a OR).
• Inflation: up to 40% of the rise in the Swiss consumer price index (art. 16 VMWG).
• Higher costs: maintenance, fees, insurance, documented.
• Value-adding investments: renovations that add value, such as an energy upgrade or a new kitchen; a cosmetic refresh does not count.
• Rents usual in the area (art. 269a OR).

How to contest it

1. Within 30 days of receiving the notice (art. 270b OR)
2. At the cantonal conciliation authority (Schlichtungsbehörde); the procedure is free
3. While the case runs, the lease continues unchanged (art. 270e OR)
4. The Mieterverband can help with the paperwork; see what the Mieterverband does

Graduated and indexed rents

With a Staffelmiete (graduated rent) the steps are fixed in francs at signing; the lease must run at least three years, with at most one step a year (art. 269c OR). Since 1 October 2025 a step needs no official form, but the landlord must announce it in writing, no earlier than four months before it applies (art. 269d para. 5 OR, art. 19a VMWG). You can contest only the initial rent, not the steps (art. 270d OR). An Indexmiete (indexed rent) still needs the official form.

General information, not legal advice.

• OR art. 269a (fedlex.admin.ch)
• OR art. 269d (fedlex.admin.ch)
• OR art. 270a (fedlex.admin.ch)
• OR art. 270b (fedlex.admin.ch)
• OR art. 270e (fedlex.admin.ch)
• OR art. 269c, Staffelmiete (fedlex.admin.ch)
• OR art. 270d (fedlex.admin.ch)
• VMWG art. 13 (fedlex.admin.ch)
• VMWG art. 16 (fedlex.admin.ch)
• VMWG art. 19a (fedlex.admin.ch)
• BWO, Referenzzinssatz (bwo.admin.ch)
• Bundesrat, Referenzzinssatz 1 September 2026 (admin.ch)