Short answer. If someone dies without children or other descendants, but is survived by legitimate parents, the law reserves one-half of the estate for those parents as their legitime. This half cannot be taken away by will. The deceased may freely dispose of the remaining half, subject to other heirs' rights.
What the law says
The legitime of legitimate parents or ascendants consists of one-half of the hereditary estates of their children and descendants.
Civil Code, Article 889 — Legitime of Legitimate Parents. Read the full provision →
The half that belongs to the parents by law
Article 889 makes legitimate parents compulsory heirs whenever their child dies leaving no children or other descendants. The legitime of legitimate parents or ascendants consists of one-half of the hereditary estates of their children and descendants. That half is not a suggestion or a default that a will can override — it is reserved to the parents by operation of law. A will that tries to give the whole estate to someone else, or that cuts the parents' share below one-half, is invalid to that extent, and the parents can demand their legitime regardless of what the will says.
The other half is not automatically free
The article itself says the child "may freely dispose of the other half, subject to the rights of illegitimate children and of the surviving spouse as hereinafter provided." So the remaining half is not simply extra money for whoever the will names. If the deceased also left illegitimate children or a surviving spouse, their shares come out of that same estate and can reduce what is actually left at free disposal. Only after those competing claims are accounted for does it become clear how much of the second half the deceased genuinely controlled through the will.
"Parents or ascendants" reaches beyond mother and father
The provision does not say only "parents" — it says parents or ascendants. That wording exists because a legitime for the ascending line has to work even where the immediate parents are no longer living but a grandparent is. The one-half legitime is a share reserved for that whole line, not a right that disappears the moment the nearest generation is gone. Who exactly within that line receives the half, and in what proportions among several surviving ascendants, is a separate question from the size of the reserved share itself, which this article fixes at one-half.
Why this only applies when there are no descendants
This one-half legitime for parents only comes into play because the deceased left no children or other descendants. Where descendants exist, they are the ones with the primary and larger claim on the estate, and parents are pushed out of the compulsory-heir picture entirely for that purpose. So the practical first question in any estate is always whether the deceased left any children, grandchildren, or other descendants — because that answer decides whether Article 889 applies to the parents at all, or whether it has no role to play.