How the calculations work
Each calculator applies the formula that the country’s law sets, with the series published by the competent statistics office, rounded the way the law asks.
France
Residential rent review: rent excluding charges × IRL for the reference quarter this year / IRL for the same quarter a year earlier, rounded to the cent (Law of 6 July 1989, art. 17-1). Mainland France, Corsica and the overseas departments have separate Insee series. Homes rated F or G cannot have their rent reviewed if the lease was signed, renewed or rolled over since 24 August 2022 (mainland) or 1 July 2024 (overseas). Commercial leases use the ILC or ILAT the same way; child support uses the consumer price index excluding tobacco.
Belgium
Base rent × new health index / starting index (base 2013: Statbel for the last 13 months, the Brussels Housing calculator for the history). The starting index is the month before signing in Brussels and Wallonia, and the month before the lease took effect in Flanders; the new index is the month before the anniversary. The Brussels and Flemish correction factors and the Walloon cap of 2022-2023 follow the regional governments’ pages. The 2016 index skip is not modelled.
Spain, Italy, Portugal, Austria
Spain: annual change in the CPI or IRAV for the latest month published by INE, with the caps of the Urban Leases Act and Royal Decree-law 29/2026. Italy: annual change in the FOI index excluding tobacco, at 75% or 100% depending on the lease, with Istat’s base-linking coefficients. Portugal: coefficients published in the Diário da República, up to three years caught up, rounded up to the next cent. Austria: average CPI change of the previous year under the MieWeG, with half of the share above 3% counted.
Updates and limits
The series are refreshed by a script that queries the official interfaces (Insee, Statbel, INE, Istat, Statistik Austria); the Portuguese coefficients, the Flemish factors and Istat’s linking coefficients are updated by hand. On each run the script also reads the status of Royal Decree-law 29/2026 in the BOE API: if it is shown as repealed, the update fails and the site is not republished until the calculation is corrected. A calculation does not replace reading the lease: a specific clause (another index, a floor, its own date) overrides the general case, and a court may decide a disputed case differently.
Frequently asked questions
Which statistics offices supply the figures used on this site?
Insee for the French IRL, ILC, ILAT and consumer prices; Statbel for the Belgian health index; INE for the Spanish CPI and IRAV; Istat for the Italian FOI index and its linking coefficients; Statistik Austria for the VPI. The Portuguese coefficients are read in the notices that INE publishes in the Diário da República. The Portuguese coefficients, the Flemish correction factors and Istat’s linking coefficients are entered by hand; the other series are downloaded by a script. Each value carries the date it was last read.
Are the indices ever rounded before the rent is worked out?
No. The calculation always uses the index values exactly as published, and only the result is rounded: to the nearest cent in France, Belgium, Spain, Italy and Austria, and up to the next cent in Portugal, as its tenancy law requires. The percentage shown next to the result is rounded to two decimals for reading only.
What happens if I pick a month whose index is not out yet?
The calculator says the value is not yet published and tells you roughly when the statistics office usually releases it. It never fills the gap with a forecast, because a rent review based on a guess is worth nothing to either side. Come back after the release date, or use the latest published month if your lease allows it.
Official sources
- Insee, rent reference index (IRL) series 001515333
- Insee, IRL for Corsica, series 010760507
- Insee, IRL for the overseas departments, series 010760509
- Insee, commercial rent index (ILC), series 001532540
- Insee, office rent index (ILAT), series 001617112
- Insee, consumer price index excluding tobacco, all households, base 2025, series 011814056
- Insee, revising child support (Réviser une pension alimentaire)
- Insee, reuse terms (Licence Ouverte 2.0)
- Service-public.fr, revision of a home’s rent (F13723)
- Service-public.fr, annual uprating of child support (F2010)
- French Law 89-462 of 6 July 1989, articles 17-1 and 17 (Légifrance)
- Statbel, health index
- Statbel, gezondheidsindex (Dutch page)
- Statbel, health index
- be.brussels, rent indexation with a correction factor
- Wallonie.be, indexing a rent
- Vlaanderen.be, rent indexation with correction factors
- Spanish Urban Leases Act 29/1994, consolidated text (BOE)
- Royal Decree-law 29/2026 of 6 October (BOE-A-2026-20823)
- INE, consumer price index (IPC), latest figures
- INE, methodology of the housing lease update index (IRAV)
- Istat, consumer price index for monetary revaluations (FOI)
- Istat, Rivaluta service (base-linking coefficients)
- Italian Law 392 of 27 July 1978, art. 32 (Normattiva)
- Italian Law 431 of 9 December 1998 (Normattiva)
- Italian Legislative Decree 23 of 14 March 2011, art. 3(11) (cedolare secca, Normattiva)
- Diário da República, Notice 24199/2026/2 (2027 coefficient)
- Diário da República, Notice 23174/2025/2 (2026 coefficient)
- Diário da República, Notice 23099/2024/2 (2025 coefficient)
- Diário da República, Notice 20980-A/2023 (2024 coefficient)
- Portuguese Law 19/2022 of 21 October (2023 coefficient set at 1.02)
- Statistics Portugal (INE), releases
- Austrian Rent Value-Protection Act (MieWeG), Federal Law Gazette I 114/2025 (RIS)
- Austrian Tenancy Act (MRG), current version (RIS)
- Statistik Austria, consumer price index (VPI/HVPI)
Written by Radif Partners
Publisher of rent indexation calculators for France, Belgium, Spain, Italy, Portugal and Austria
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Official indices checked in 2026, site checked on