Short answer. Generally no. Article 2213 of the Civil Code says interest cannot be recovered upon unliquidated claims or damages — unless the demand can be established with reasonable certainty. Until the amount is fixed or can be reasonably ascertained, interest does not run on it.
What the law says
Interest cannot be recovered upon unliquidated claims or damages, except when the demand can be established with reasonable certainty.
Civil Code, Article 2213 — No Interest on Unliquidated Claims. Read the full provision →
The general rule
Article 2213 provides that Interest cannot be recovered upon unliquidated claims or damages, except when the demand can be established with reasonable certainty. An unliquidated claim is one whose amount is not yet settled — it still depends on proof, computation or the court's determination. The law's starting point is that you cannot charge interest on a sum that is not yet known, because there is no fixed figure on which interest could sensibly be reckoned.
The exception that matters
The article does not close the door entirely. It allows interest when the demand can be established with reasonable certainty. Where the amount, though not formally liquidated, can be worked out with reasonable certainty from the facts, the claim is treated differently and interest may attach. The dividing line is certainty: the more the sum can be pinned down without guesswork, the closer it moves to a claim on which interest can be recovered.
How this plays out
In practice this means the timing of interest often turns on when a claim becomes certain — for instance, when the amount is finally determined. Before that point, an open, disputed or estimated figure will usually carry no interest under this article. The provision governs the entitlement to interest on the claim itself; it does not fix the rate or resolve how the principal is proved. If interest on a sum matters to your case, keep the records that make the amount ascertainable, because the certainty of the figure is what decides whether interest can be claimed at all.
What the exception does not cover
It helps to see what the exception does not reach. A figure is not made certain merely because the claimant asserts one; the amount has to be capable of being worked out from the facts and the evidence, not from the plaintiff's own say-so, and the burden of showing that certainty rests on the party seeking the interest. This article speaks to interest on unliquidated claims and damages. It does not touch interest that the parties have themselves agreed to in a loan or contract, which stands on a different footing and runs by its own terms regardless of whether the claim is liquidated. Nor does it set the rate; it decides only whether interest may be recovered at all.