Homeowners May Be Overpaying IMI, DECO PROteste Warns: a Revaluation Request Before 31 December Could Lower Next Year's Bill
A home's taxable value does not fall on its own as the building ages, so some owners pay more IMI than a new valuation would give. DECO PROteste advises a simulation first: a revaluation can also raise the bill, and it locks in for three years.
Some homeowners in Portugal are paying more Imposto Municipal sobre Imóveis (IMI, the municipal property tax) than they need to, DECO PROteste warned on 26 October, because the tax value of their home has not kept pace with its age. The consumer organisation advises a simulation first, since a revaluation can also push the bill up. According to Lusa, reported by RTP, it comes ahead of the last IMI instalment in November.
Why the tax value can be out of date
IMI is charged on a home's Valor Patrimonial Tributário (VPT, the taxable property value). Under Article 38 of the IMI Code, that value multiplies a base value per square metre by the building's area and coefficients for use, location, quality and age. The age factor, the coeficiente de vetustez (age coefficient), falls in steps: from 1 for a home less than 2 years old to 0.75 at 26 to 40 years, 0.65 at 41 to 50, 0.55 at 51 to 60 and 0.40 after 60 years (Article 44).
The Autoridade Tributária e Aduaneira (AT, the Tax and Customs Authority) updates tax values every three years by applying an inflation coefficient (Article 138), but it does not recalculate the age or location coefficients. DECO notes that these updates, as a rule, only raise the tax.
Why a new valuation can also cost you more
For 2026 the government set the average construction value at 570 euros per square metre in Portaria n.º 471/2025/1 (Ministerial Order 471/2025/1), which applies to valuation requests delivered from 1 January 2026. Adding the land component of 25 percent (Article 39) gives a base value of 712.50 euros per square metre. If a home was last valued on a lower base value, the new one can cancel out the age discount, so DECO tells owners to apply only once a simulation shows a gain.
A value set by direct valuation can only be challenged as out of date again three years after the request (Article 130), so an unfavourable result stays for at least three years.
Rates and the payment calendar
Each municipal assembly sets the rate for urban property between 0.3 and 0.45 percent of the VPT; rural land pays 0.8 percent (Article 112). A bill of up to 100 euros is paid in full in May; between 100 and 500 euros, in May and November; above 500 euros, in three instalments in May, August and November (Article 120). A revaluation requested now will not change the November instalment.
Separately, the 2027 Budget would extend IMI and IMT breaks on restored old buildings to 2031.
What it means for you
- Check the dates: a correction takes effect in the tax for the year in which you ask (Article 130), and that tax is billed the following spring. A request made by 31 December 2026 can therefore lower the IMI you pay in 2027.
- Simulate first: the AT's own property value simulator shows the location coefficient for your address and estimates a new value; its results are for information only. DECO also offers a free simulator.
- Applying: the request is made on the Modelo 1 do IMI (IMI Form 1) on the Portal das Finanças, choosing "Pedido de Avaliação" with the reason that the VPT is out of date. DECO says the request is free.
- The key ages: the coefficient falls at 2, 9, 16, 26, 41, 51 and 61 years, so homes that have just crossed one are likeliest to gain.
