Challenging a rent increase: official form, deadline and reasons

The landlord can only raise the rent with effect from the next termination date. You must be notified of the increase at least ten days before the notice period begins, on a form approved by the canton and stating the reasons (Art. 269d CO).

The increase is void in any of these cases:

• It does not come on the official form but, for example, only as a letter or an email.
• It gives no reasons, or only vague ones.
• It is coupled with notice of termination or the threat of it.

If the notification arrives too late, the increase only takes effect on the following termination date. An example: with three months' notice to the end of March, the notice period starts on 1 January. The increase must then reach you by about 20 December at the latest.

An increase is only permitted if the new rent is not abusive (Art. 269 and 269a CO). What counts are the changes since the rent was last set. The most common grounds:

• Rising reference interest rate: for every rise of 0.25 percentage points, up to 3 percent more rent is permitted as long as the rate is below 5 percent (Art. 13 VMWG).
• Inflation: at most 40 percent of the rise in the Swiss consumer price index since the last adjustment (Art. 16 VMWG).
• General cost increases: higher costs for maintenance, fees or insurance. Many landlords apply a flat rate of 0.5 to 1 percent a year for this. You can demand proof of the actual costs.
• Value-enhancing investments: for example a lift, new balconies or better insulation. In a comprehensive renovation, 50 to 70 percent of the costs usually count as value-enhancing (Art. 14 VMWG). Mere repairs do not count.
• Customary rents in the neighbourhood: the landlord has to back this up with at least five comparable flats. That rarely succeeds.

Grounds for a reduction count too. If the reference interest rate initially fell after the rent was last set and that cut was never passed on to you, you can offset it against the increase. The reference rate calculator shows what one step is worth.

1. Check the form

   Without the official form or without reasons, the increase is void. If it arrived too late, it only takes effect on the next termination date.

2. Verify the calculation

   Note the reference interest rate and the consumer price index as they stood when the rent was last set. They are usually stated in the lease or on the last form. Compare them with today's figures and with the increase demanded.

3. Ask for evidence

   For cost increases or investments, you are entitled to see the underlying invoices. Ask for them in writing.

4. Contest within 30 days

   Your request must reach the conciliation authority where the flat is located within 30 days of receiving the form (Art. 270b CO). A short letter is enough. The procedure is free of charge (Art. 113 CPC).

5. Keep paying the current rent

   During the proceedings the existing lease continues unchanged (Art. 270e CO). If the increase is upheld in full or in part, you pay the difference afterwards.

If the landlord gives you notice because you are fighting an increase, you can contest it (Art. 271a CO). The protection applies during the conciliation and court proceedings and for three years afterwards if you won in full or in part or if you reached a settlement.

Exceptions include notice for arrears, for a serious breach of the tenant's duties or because the landlord urgently needs the flat for personal use. So always pay the rent in full and on time.

• Missing the 30 days. After that, a formally correct increase counts as accepted.
• Protesting only to the landlord instead of contesting the increase at the conciliation authority.
• Simply not paying the higher rent without contesting it or explaining in writing why it is void.
• Not checking for earlier reductions you never received, which can be offset.
• Taking the stated reasons at face value. Flat rates and investments must be backed by evidence.