Short answer. Only property acquired through actual joint contribution is co-owned, in proportion to what each contributed. And the married partner's share does not stay with the relationship: it accrues to the absolute community or conjugal partnership of the existing valid marriage.

What the law says

only the properties acquired by both of the parties through their actual joint contribution of money, property, or industry shall be owned by them in common in proportion to their respective contributions

Family Code, Article 148 — Property of Unions Without Marriage (Not Capacitated). Read the full provision →

What the law says

If one of the parties is validly married to another, his or her share in the co-ownership shall accrue to the absolute community or conjugal partnership existing in such valid marriage.

Family Code, Article 148 — Property of Unions Without Marriage (Not Capacitated). Read the full provision →

You must have actually contributed, and you must prove it

Where one partner is still married to someone else, the couple falls under Article 148 of the Family Code, which is markedly stricter than the rule for partners who are both free to marry. Co-ownership covers only the properties acquired by both of the parties through their actual joint contribution of money, property, or industry, and each takes a share in proportion to their respective contributions. Actual contribution is the operative phrase: unlike the regime for capacitated partners, care of the household and the family is not treated here as a contribution that buys a share.

Equal shares are only a starting presumption

The article softens the proof problem slightly. In the absence of proof to the contrary, their contributions and corresponding shares are presumed to be equal, and the same rule applies to joint deposits of money and evidences of credit. But this presumption operates only once joint acquisition is established, and it can be displaced by evidence of what each side actually put in. In practice that makes receipts, deposit records, loan documents and remittance histories the substance of these cases. Property bought entirely by one partner does not become shared merely because the couple lived together while it was acquired.

The married partner's share goes to the marriage

Then comes the provision that surprises people most. If one of the parties is validly married to another, his or her share in the co-ownership shall accrue to the absolute community or conjugal partnership existing in such valid marriage. The married partner does not personally keep their half — it flows to the property regime of the subsisting marriage, and so, in substance, to the legal spouse. The article also provides for forfeiture of a bad-faith party's share, and applies those forfeiture rules even where both parties are in bad faith. Anyone in this situation should get the ownership question assessed before, not after, buying property together.

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.