French development tax 2026: calculation, rate per m²

Who pays, and for which works?

The tax is levied by the municipality, the département and, in Île-de-France only, the region, when a planning authorisation is granted: permis de construire (building permit), déclaration préalable (prior declaration of works), etc. (ecologie.gouv.fr). It covers construction, reconstruction and extensions, as well as certain installations such as swimming pools, garden sheds or parking spaces.

The person liable is the holder of the authorisation (or the person responsible for an unlawful construction). For authorisations granted since 1 September 2022, the tax is payable on the date of completion of the works (collectivites-locales.gouv.fr; art. 1635 quater G of the CGI). The person liable declares the necessary details within 90 days of that date (art. 1635 quater P of the CGI).

The flat-rate value per m²: €892 or €1,011 in 2026

Source: BOFiP, BOI-IF-TU-10-30-10. The values are revised on 1 January in line with the Insee (national statistics institute) construction cost index and rounded down to the nearest euro. In 2026, they fall compared with 2025.

Some installations have their own value (art. 1635 quater J of the CGI, version in force since 1 July 2026):

The 50% allowance does not apply to these installations, in particular swimming pools and outdoor parking spaces (BOFiP, BOI-IF-TU-10-30-20).

The 50% allowance on the first 100 m²

Article 1635 quater I of the CGI provides for a 50% allowance on the flat-rate value for the first hundred square metres of residential premises and their outbuildings used as a main residence. The BOFiP specifies:

• the main residence is understood as for income tax; it may be that of the builder, the future owner or the future tenant;
• the outbuildings concerned are cellars, ground-floor storerooms, lean-tos, and enclosed and covered parking areas; outdoor spaces are excluded;
• in a block of flats, the 100 m² are assessed dwelling by dwelling; the unused portion of a small dwelling is not carried over to a large one;
• for an extension, the new floor area is added to that of the existing home to determine whether the 100 m² threshold has already been reached.

The 50% rate cannot be changed by local authorities. Légifrance indicates that the current version of article 1635 quater I is in force until 1 January 2027: check the applicable rule if your works are completed after that date.

The rates and a worked example

Rates voted before 1 July apply the following year. The rate for your area is set out in the resolutions of the municipality and the département.

Example (hypothetical rates). New house with 120 taxable m², main residence, outside Île-de-France, municipality at 5%, département at 2.5%:

• 100 m² × €446 = €44,600;
• 20 m² × €892 = €17,840;
• basis = €62,440;
• municipal share: €62,440 × 5% = €3,122;
• département share: €62,440 × 2.5% = €1,561;
• total: €4,683.

A 30 m² swimming pool would add 30 × €251 = €7,530 to the basis, i.e. €564.75 at the same rates. The DGFiP (French tax authority) offers an official simulator on impots.gouv.fr.

Exemptions

Automatic, in particular: constructions of 5 m² or less, like-for-like reconstruction after a disaster, certain social housing financed by a subsidised loan, parking areas built into the building (collectivites-locales.gouv.fr).

Optional, voted by each local authority for its own share: for example garden sheds, main residences financed by a PTZ (prêt à taux zéro, interest-free loan) (for part of the floor area above 100 m²) or listed historic monuments. The 2026 Finance Act (art. 115) amended the optional exemptions for shops and garden sheds (BOFiP, news item of 26 August 2026): ask your mairie (town hall) which resolution is in force.

Which professional to consult

The géomètre-expert (chartered land surveyor) measures the taxable floor area and can establish it for your planning application. When you buy a plot of land, the notaire (the public official who drafts property deeds) tells you about any tax to come. The courtier en crédit (mortgage broker) can include its amount in the budget for your building project.