Short answer. Yes, if the creditor formally extended the payment term without your consent, the guaranty is extinguished. Article 2079 of the Civil Code is clear: an extension granted to the debtor without the guarantor's consent extinguishes the guaranty. However, the creditor merely delaying collection without a formal extension does not have the same effect.
What the law says
An extension granted to the debtor by the creditor without the consent of the guarantor extinguishes the guaranty. The mere failure on the part of the creditor to demand payment after the debt has become due does not of itself constitute any extension of time referred to herein.
Civil Code, Article 2079 — An Extension Given Without the Guarantor's Consent. Read the full provision →
Why an unauthorized extension releases the guarantor
A guarantor signs on to ensure that a specific obligation is paid by a specific time. When the creditor and debtor privately agree to extend the payment deadline, they are effectively creating a new arrangement that the guarantor never agreed to back. The guarantor is left exposed for a longer period than they bargained for, on a debt that has been restructured without their input. Article 2079 responds to this unfairness by treating the unauthorized extension as extinguishing the guaranty entirely. The creditor cannot alter the terms of the underlying deal and then hold the guarantor to the original guaranty.
The critical distinction: extension versus delay
Article 2079 draws a careful line. A formal extension — where the creditor and debtor agree the debt will not be due until a later date — extinguishes the guaranty. But the creditor's mere failure to demand payment after the debt becomes due does not constitute an extension. If the creditor simply waits a few months before collecting, that inaction does not change the due date and does not release you. The release requires a genuine agreement between creditor and debtor that changes when the debt is owed — not just creditor passivity.
What evidence of an extension looks like
To invoke Article 2079, you need to show that a real extension was granted — that there was some agreement, express or implied, between the creditor and debtor to postpone the payment date. Written evidence is most convincing: a letter from the creditor to the debtor saying "you may pay by [new date]," a restructuring agreement, or a new promissory note with a later due date. If the only thing that happened was that the creditor sent no demand after the due date, Article 2079 explicitly says that is not enough. The factual question of whether an extension was truly granted is often where these disputes turn.
Protecting yourself going forward
If you are currently a guarantor and worried about this scenario, request that the loan documents include a clause requiring the creditor to notify you of any proposed change to the payment schedule and obtain your written consent before any extension is effective. Without such a clause, the law protects you through Article 2079 — but you would still need to raise the defense and prove the extension was granted without your consent. A contractual notice requirement makes the analysis simpler if a dispute arises.