The base value that serves as a reference for calculating the Municipal Property Tax (IMI) will increase in 2026. From next year, the price per square meter for IMI purposes will be 712.5 euros, an increase that results from the annual update of the average construction value defined by the Government and published in the Diário da República.
The decision is contained in an ordinance that sets the average construction value per square meter at 570 euros, plus the legal coefficient of 25 percent. All things considered, the relevant value for tax purposes rises from the current 665 euros to 712.5 euros, representing a new level in the calculation of the taxable heritage value of urban buildings.
According to Notícias ao Minuto, this update applies from January 1, 2026 and is the result of a proposal from the National Commission for the Assessment of Urban Buildings, the entity responsible for monitoring the evolution of construction costs and proposing the values to be adopted annually.
What exactly is changing
The ordinance now published sets the average construction value at 570 euros per square meter for the purposes of article 39 of the Municipal Property Tax Code. This value serves as the basis for the IMI calculation formula, and is then increased by 25 percent, as determined by law.
According to the official publication, this is one of the objective elements that make up the evaluation system for urban buildings, together with factors such as the area, location, construction quality and age of the property. The final result of this formula is the tax asset value, which is subject to the IMI rate defined by each municipality.
Not an automatic raise for everyone
Despite the increase in the base value, application is not automatic to all properties. According to the legal framework explained by Notícias ao Minuto, this new value is only reflected in urban buildings whose Model 1 declarations are delivered from January 1, 2026.
In practice, this means that the update mainly affects new constructions, properties subject to expansion, reconstruction or relevant alterations, as well as situations in which a new assessment of the building is triggered. Properties already evaluated and without changes do not see their IMI changed just by this update of the base value.
A value that has been rising over the years
The price history per square meter for IMI purposes shows an evolution marked by long periods of stability and specific adjustments. In 2003 and 2004, the base value was 600 euros. It rose to 612.5 euros in 2005 and to 615 euros in 2006, a level that remained until 2008.
With the financial crisis, in 2009 there was a drop to 609 euros, followed by a further reduction in 2010, to 603 euros. This value remained frozen until 2018. In 2019 it rose again to 615 euros, remaining that way until 2021. In 2022 it increased to 640 euros, in 2023 to 665 euros, a value that remained in 2025. In 2026, the jump takes the indicator to 712.5 euros.
According to , this trajectory reflects the attempt to follow the evolution of construction costs, which have registered significant increases in recent years, driven by the price of materials and labor.
Or real impact not bag
Although it is a relevant element, the base value per square meter is only one piece of the IMI equation. The location of the property, the municipal coefficients and the state of conservation continue to have a determining impact on the final tax payable.
Still, for those who are building a house, carrying out extensive works or requesting a new assessment, the new value can translate into a higher asset value and, consequently, a higher IMI.
The update now announced does not change municipal taxes or change structural tax rules. But it confirms a gradual upward trend that, in certain cases, could have a direct impact on owners’ annual bills from 2026 onwards.
Also read:
