Short answer. Only if the mistake was a serious one. It must concern the substance of the thing contracted for, or the very conditions that principally moved you to agree. Regret, a bad bargain, or a detail you did not bother to check is not enough to undo a contract.
What the law says
In order that mistake may invalidate consent, it should refer to the substance of the thing which is the object of the contract, or to those conditions which have principally moved one or both parties to enter into the contract.
Civil Code, Article 1331 — Mistake (Error). Read the full provision →
The mistake has to go to the heart of the deal
The law does not rescue every misunderstanding. It asks whether the error touched the substance of the thing — what the object essentially is — or the conditions that principally moved you to contract. Buying a lot in the belief that it was a different lot altogether goes to substance. Buying stones sold and understood as gemstones which are in fact glass goes to substance. Buying land at a price you now think too high, or discovering that a neighbouring development will not proceed, generally does not. The test is whether, absent the error, this contract would not have been made at all — not whether you would have negotiated harder.
Mistakes about the other party, and simple errors of computation
Two situations get their own treatment. A mistake as to the identity or qualifications of the other party vitiates consent only when that identity or those qualifications were the principal cause of the contract — hiring a specific licensed engineer because of that expertise, for instance, as against buying an ordinary commodity where the seller's identity is immaterial. And an arithmetical slip is not a ground to unravel anything: the article says "A simple mistake of account shall give rise to its correction." If the figures were added wrongly, the remedy is to fix the sum, not to void the agreement.
The consequence: voidable, not void
A contract tainted by this kind of mistake is voidable, which is a very different thing from void. It is valid and binding — enforceable against you — until it is annulled in a proper action. That has three practical consequences. You must act rather than simply stop performing. There is a prescriptive period for bringing the action, counted from the discovery of the mistake, so delay can extinguish the remedy entirely. And continuing to perform after you learn the truth, by accepting benefits or making further payments, can amount to ratification and close the door for good.
What weakens a mistake claim
The most common answer to this argument is that the mistake was your own fault. A party who had the document in hand, could read it, had the chance to inspect the property, or was given the figures and chose not to look will struggle. Signing without reading is rarely treated as an excusable error. Mistake also has neighbours in the law — fraud, intimidation and undue influence — and a case is often stronger framed as one of those if the other side caused or exploited your error. Which framing fits depends on documents and evidence, and this is general information rather than advice.
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.
- Cebu Windland Development Corporation vs. Ong Siao Hua, G.R. No. 173215, May 21, 2009 — read the decision on LawPhil →
- Park Developers, Incorporated, et al. vs. Elizabeth D. Daclan, G.R. No. 211301, November 27, 2019 — read the decision on LawPhil →
- Dr. Rico Vargas Substituted By His Wife, Cecilia Vargas And Children, Namely: Richelle Josie Judy Vargas-castro, Arvee T. Vargas And Cecilia Vargas, vs. Jose F. Acsayan, Jr, G.R. No. 206780, March 20, 2019 — read the decision on LawPhil →
- William Uy & Rodel Roxas vs. Court of Appeals, et al, G.R. No. 120465, September 9, 1999 — read the decision on LawPhil →