Index rent calculator
Calculate the index-linked rent from the consumer price index: base month per contract, current comparison month, previous rent. Optionally we check whether a threshold is reached. Index values come straight from Statistik Austria, Destatis and the SNB; for other countries or older series you enter the values yourself.
How the calculation works
The indexation clause in the lease ties the rent to an index — in Austria usually the CPI, in Germany the consumer price index (index rent under § 557b BGB), in Switzerland the national consumer price index. The contract names a base month; its index value is the starting point.
The new rent equals the old rent multiplied by the ratio of the current index value to the base index value. Many clauses include a threshold: only once the index has risen by more than, say, 5 percent may the rent be adjusted. The adjustment month then becomes the new base.
Whether and from when an adjustment is permitted depends on the contract, the applicable tenancy law and formal requirements. The calculator delivers the arithmetic and the source; the legal assessment stays with you or your adviser.
Frequently asked questions
The month the indexation clause refers to — usually the month the contract was signed or the last adjustment. It is in the lease or the last adjustment letter.
Statistics offices publish the index with a delay, in Austria usually mid of the following month as a provisional value. Choose the last published month.
Austria: CPI 2020 = 100 from Statistik Austria. Since January 2026 the CPI 2025 is published; Statistik Austria continues the CPI 2020 by chaining (CPI 2025 × 1.282, rounded to one decimal), and the calculator uses exactly these values. Germany: CPI 2020 = 100 from Destatis. Switzerland: LIK from the SNB. If your contract names another series (e.g. CPI 2010 or CPI 2015) or another country, choose “Enter index values” and use the values of that series.
No. The calculation runs without an account; inputs are not stored and not linked to persons.
Apply the adjustment directly in the lease?
In immoMonk the contract fetches the index itself, checks the threshold and generates the adjustment letter as PDF. Free during the open beta.