Plusvalía municipal
The municipal tax on the increase in urban-land value, paid by the seller (not the buyer) on standard resales.
Plusvalía municipal (formally the Impuesto sobre el Incremento de Valor de los Terrenos de Naturaleza Urbana, or IIVTNU) is a municipal tax on the increase in urban-land value over the time the seller owned the property.
It is calculated by the municipality based on the cadastral land value and the years of ownership. Following the 2021 Constitutional Court ruling and subsequent reform, the formula now allows either an objective calculation method or an actual-gain method, and the seller can choose the lower of the two.
On a standard resale, plusvalía is paid by the seller, not the buyer. Make sure this is explicitly stated in your purchase contract. Some sellers try to push it onto the buyer; the standard market practice is seller-paid.
Exception: if the property has lost value over the seller's ownership period (i.e. you can prove no plusvalía gain occurred), the tax is now waived. This is a 2022 reform.