Short answer. Yes. Article 1273 provides that the renunciation of the principal debt shall extinguish the accessory obligations. Interest and a guaranty are accessory to the principal loan, so forgiving the principal drags them down with it. The reverse is not true: waiving only the interest or the guaranty leaves the principal debt itself in force.
What the law says
The renunciation of the principal debt shall extinguish the accessory obligations
Civil Code, Article 1273 — Remission of Principal vs. Accessory. Read the full provision →
What the law says
the waiver of the latter shall leave the former in force
Civil Code, Article 1273 — Remission of Principal vs. Accessory. Read the full provision →
Accessory obligations follow the principal
Article 1273 states a short but powerful rule: The renunciation of the principal debt shall extinguish the accessory obligations. Philippine law divides obligations into a principal one, here your duty to repay the loan itself, and accessory ones that exist only to support it. An accessory obligation has no independent life; it is attached to the principal and serves it. So when the creditor forgives the principal debt, the law treats the supports as falling away with it. There is nothing left for them to secure or attach to, so they are extinguished by operation of the article, not by any separate act of forgiveness.
Interest and the guaranty are both accessory
Your two worries, interest and the guaranty, are classic accessory obligations. Interest is a charge that rides on the principal loan; a guaranty is a security given by a third person to answer if you do not pay. Neither stands on its own: interest presupposes a principal sum to run on, and a guaranty presupposes a principal debt to guarantee. Once the principal is renounced, the interest has no base to accrue on and the guarantor has nothing left to answer for. Under Article 1273, forgiving the principal therefore wipes out the accrued or future interest tied to it and releases the guaranty as well.
It does not work in reverse
The article is deliberately one-directional. Its second half says the waiver of the latter shall leave the former in force. So if the creditor had instead forgiven only the interest, or released only the guarantor, your duty to repay the principal would survive untouched. Cancelling a support does not cancel the thing it supports. This matters when a creditor is willing to give up something small, say waive penalties or free a guarantor, without intending to forgive the loan itself. Read carefully what was actually renounced: forgiving the principal frees everything, but forgiving an accessory frees only that accessory.
What still has to be true
Two cautions before you rely on this. First, there must be a real renunciation of the principal, a genuine act of the creditor forgiving the loan, not a vague promise or a partial concession. If what the creditor gave up was only part of the debt, or was really just a restructuring, the accessory obligations may not fall. Second, the rule reaches obligations that are truly accessory to this loan. A separate, independent debt you owe the same creditor is not an accessory of the forgiven one and is unaffected. And where others are also bound, their positions depend on the exact terms of what was forgiven.