Short answer. A calculation error gives you the right to correction, not annulment. Article 1331 of the Civil Code is explicit: a simple mistake of account gives rise only to its correction. Annulment requires a mistake that goes to the substance of the contract or the conditions that moved the parties to agree.
What the law says
A simple mistake of account shall give rise to its correction.
Civil Code, Article 1331 — Mistake (Error). Read the full provision →
Correction, not annulment
Article 1331 of the Civil Code draws a clear line between mistakes that can void or annul a contract and mistakes that merely need to be fixed. A calculation error — the wrong total, a misplaced decimal, an arithmetic slip — falls squarely into the second category. The law calls this a simple mistake of account and says it gives rise only to its correction. You are entitled to have the figure put right, but the contract itself stands. You cannot use a math error to walk away from an agreement you otherwise freely entered.
What kind of mistake actually invalidates consent
For a mistake to rise to the level of vitiating consent — making the contract voidable — it must concern the substance of the thing that is the object of the contract, or the conditions that principally moved one or both parties to agree. That means a fundamental error about what you are contracting over: you thought you were buying a titled lot, but the property is untitled; you believed you were hiring a licensed engineer, but the person has no license, and that credential was the whole reason you signed. Those go to the root of the agreement. A wrong total on the face of the contract does not.
What the correction process looks like
In practice, correction is handled either by a supplemental agreement that both parties sign acknowledging the error and fixing the number, or — if the other party refuses to cooperate — by an action for reformation of the instrument. The goal of reformation is to make the written contract reflect what the parties actually agreed to. If both sides accept that the total is wrong and agree on the right figure, a written correction signed by both is simpler and faster than going to court. Document the error clearly: show the calculation, the wrong figure, and what the correct figure should be.
When the other party disputes the correction
If the other party insists the figure in the contract is correct, or claims the number was intentional and not an error at all, the matter becomes a factual dispute. You would need to show that the total resulted from a genuine arithmetic mistake — not a deliberate pricing choice, not a negotiated number, but an error in computation. Gather the underlying calculations, the invoices or unit prices that the total was supposed to reflect, and any correspondence that shows what figure was actually discussed and agreed upon. Those documents are the foundation of any claim for correction.
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 →