Does the mortgage reference interest rate also apply to index rent (national index of consumer prices)?

Index rent vs. reference interest rate

No, the reference mortgage interest rate does not apply to real index rentals. According to Art. 269b OR, the rent in the case of index rent may only be adjusted in accordance with the change in the national index of consumer prices (LIC). An additional increase due to higher mortgage interest rates is legally excluded. The only exception: Value-increasing investments made by the landlord can also be transferred to the rent in the case of index rent.

The principle of exclusivity: either interest or index

In 2026, the legal situation is clear: A rental agreement cannot be “a bit of both.” As soon as a valid index clause has been agreed, the path for adjustments to the reference interest rate is blocked.

Why this separation exists

The aim of index rent is to keep the purchasing power of the rent stable for the landlord while giving the tenant planning security against interest rate fluctuations.

• Risk distribution: With index rent, the landlord bears the interest rate risk, while the tenant bears the inflation risk.
• Calculation basis: While the reference interest rate reflects banks' capital costs, the LIC measures the price development of an average shopping basket (rent, food, energy).

Requirements for a valid index rent

Not every landlord is simply allowed to set an index rent. The Swiss Code of Obligations (OR) makes this subject to strict conditions, which will be carefully reviewed by the conciliation authorities in 2026.

The 5-year hurdle

For an index clause to be legally effective, the following criteria must be met:

• minimum duration: The rental agreement must have been concluded for at least five years.
• Single page index: The rent may only be linked to the official national index of consumer prices (LIC).
• Clear wording: The clause must explicitly state in the contract that adjustments are made exclusively on the basis of the LIC.

If any of these conditions are missing, the index clause is void and the reference interest rate system automatically applies again.

The exception: value-adding investments

There is one case in which the index rent may rise despite being linked to the LIK: If the landlord sustainably improves the quality of the apartment.

Increasing comfort beats index

For example, if the landlord installs a new kitchen, renovates the bathroom or carries out an energy-efficient renovation, he may add these costs (the value-increasing share) to the rent in addition to the index adjustment.

• proceedings: The landlord must also report this increase using the official form.
• computation: It is not the LIC that applies here, but the usual rates for interest and amortization of invested capital.

Strategy with heyloft.ch: Index monitoring 2026

In times of fluctuating inflation, it is crucial for tenant with index contracts to keep an eye on LIK developments. heyloft.ch offers digital tools for this purpose.

Why technological support helps with index rents

Instead of laboriously rolling through tables from the Federal Statistical Office (FSO), our system supports you:

• Index calculator: Enter your base index value from the contract. Our AI immediately calculates whether the increase required by the Gérance is mathematically correct.
• Comparative analysis: We will show you whether you are currently doing better or worse with index rent compared to a reference interest rate model in your specific district (e.g. Zurich District 4).
• Deadline check: Deadlines must also be met when it comes to index rent. We remind you when the landlord can make the next adjustment at the earliest.

Conclusion: System beats luck through clear contract review

Does the reference interest rate apply to index rents? A clear no — as long as there are no value-enhancing investments. Index rent is an “island” in Swiss tenancy law that has its own rules.

In summary, it can be stated that anyone who signs an indexed contract exchanges dependence on interest rates for dependence on inflation. This offers protection against sudden interest rate hikes, but can be expensive in times of high inflation. Use heyloft.ch's data power to professionally manage your application files and contracts. Your perfect match — calculated transparently and legally protected — only remains in place if you understand the mechanisms behind your rent.

glossary

• National Consumer Price Index (LIC): Measures the price development of goods and services that are important to private households.
• Index rent: Rental relationship in which the adjustment of the rent is linked to the development of a price index.
• Value-adding investments: Expenses by the landlord that increase the value of the home (e.g. interior design when moving into the house for the first time) and may result in additional rent.
• Tenant due diligence: Your personal due diligence. In the case of index rent, this means in particular monitoring the base index level and compliance with the 5-year period.