It is:

usufructo over a third of the estate if there are descendants ( over the third of “mejora”)

usufructo over a half of the estate if there are ascendants.

usufructo over two-thirds of the estate if there are neither ascendants nor descendants.

The reserved share in usufructo is a succession right of the surviving spouse that can be paid, at the will of the inheritors, by allocating (assigning) the property or products of certain assets, or a sum of money, to be agreed with the widow or widower or fixed by a court resolution.

If the inheritors are the step-children of the widow or widower, the surviving spouse is entitled to request to be paid his or her succession rights by being granted the ownership of certain assets or a sum of money, whichever the inheritor prefers.

An unmarried partner does not have a right to a reserved share, and the disposition of assets upon death to their benefit must respect the reserved share of possible beneficiaries from the deceased partner.

The succession rights of the surviving partner change if the succession is ruled by any of the Foral Civil Laws that exist in Spain Galicia, País Vasco, Navarra, Aragón, Cataluña, Baleares.

The inheritance will be ruled by one of such laws if the succession is of a Spaniard with the corresponding Vecindad Civil or if it is the succession of a foreigner whose last habitual residence was in one of those territories and when the deceased did not choose the law of his or her nationality to rule their own inheritance.