Short answer. Two to one. Article 983 sends you to Article 895, under which an illegitimate child takes one-half of what a legitimate child takes. The Family Code has since collapsed the old sub-classes of illegitimate children, so that single one-half ratio is what applies today.

What the law says

If illegitimate children survive with legitimate children, the shares of the former shall be in the proportions prescribed by article 895.

Civil Code, Article 983 — Shares When Both Classes Survive. Read the full provision →

What the law says

The legitime of each of the acknowledged natural children and each of the natural children by legal fiction shall consist of one-half of the legitime of each of the legitimate children or descendants.

Civil Code, Article 895 — Legitime by the Old Sub-Classes. Read the full provision →

A rule stated by cross-reference

Article 983 does not set a fraction of its own. It says that if illegitimate children survive with legitimate children, the shares of the former shall be in the proportions prescribed by article 895. So the intestate answer is borrowed from the article that fixes legitimes in testate succession, and you have to read the two together. The important consequence is that an illegitimate child is not excluded by the presence of legitimate children. Both classes inherit from the same estate at the same time; what differs is the size of the portion each one takes.

The proportion is one-half

Article 895 supplies the ratio: the legitime of the children it describes shall consist of one-half of the legitime of each of the legitimate children or descendants. One legitimate child counts as two units, one illegitimate child as one. That two-to-one relationship is the whole of the answer to how the classes rank against each other, and it is proportional rather than fixed, so it holds whatever the size of the estate and however many children there are in either class.

Ignore the old sub-classes

The language of Article 895 belongs to an older scheme that sorted children born outside marriage into categories — acknowledged natural children, natural children by legal fiction, and others — and gave each a different fraction. The Family Code did away with that classification, leaving a single class of illegitimate children. What survives of the article is the ratio it states for the first of those categories, applied now to illegitimate children generally. Reading the article's later sentences literally, as though the sub-classes still existed, is the most common error made with this provision.

Working it out on a real estate

Assign two units to each legitimate child and one to each illegitimate child, add them up, and divide the net estate by the total. Two legitimate children and one illegitimate child give five units: two-fifths, two-fifths and one-fifth. A surviving spouse complicates this, because the spouse's own share has to be satisfied out of the same estate and the fractions must be worked out together rather than in sequence. Before any of that, settle the debts and liquidate the property regime, and confirm each illegitimate child's filiation on the civil registry record.

Cases citing this provision

These Supreme Court decisions cite the provision above. We list them so you can read them yourself; the summaries of what each decided are not ours to give.

Related provisions

Note. Statute text quoted on this page is reproduced from the official enactment and is linked to the full provision. The explanation around it is general legal information from Vivas & Nobles Law Office, not legal advice. Whether it applies to your situation depends on facts only a lawyer reviewing them can assess.