Short answer. As of when the estate was partitioned, not today. Civil Code Article 1098 measures lesion by considering the value of the things at the time they were adjudicated to each co-heir, so today's market value is not the figure the one-fourth shortfall is measured against.
What the law says
considering the value of the things at the time they were adjudicated
Civil Code, Article 1098 — Rescission for Lesion. Read the full provision →
What Article 1098 allows
Article 1098 gives a co-heir a specific remedy when a partition left them shortchanged: a partition, judicial or extra-judicial, may also be rescinded on account of lesion, when any one of the co-heirs received things whose value is less, by at least one-fourth, than the share to which he is entitled. Lesion here means a real, quantifiable shortfall, not just a sense that the division felt unfair; the article sets a specific threshold, a shortfall of at least one-fourth of what the co-heir was rightfully entitled to receive, before rescission becomes available on this ground.
The valuation date the article fixes
The article does not leave the timing of valuation open to argument. It measures the shortfall considering the value of the things at the time they were adjudicated. That is the moment the partition assigned specific property to each co-heir, so the comparison is between what a share was worth at that moment and what the co-heir should have received at that same moment, not what the property is worth by the time a claim of lesion is actually raised.
Why the fixed date matters
Anchoring the comparison to the adjudication date protects the whole test from being distorted by ordinary market movement after the fact. Property that later rises or falls sharply in value does not retroactively create or erase a lesion that either did or did not exist at the moment of partition. If your share has become more valuable since the partition simply because of market changes, that increase is not evidence of a shortfall under this article; what matters is whether the values assigned to each co-heir at the time of adjudication were already off by the one-fourth margin the article requires.
What this means for building your case
Because the comparison runs off values at the time of adjudication, establishing a claim under this article generally means reconstructing what each share was actually worth at that specific point, not simply pointing to today's appraisal or market listing. Evidence closer in time to the partition itself, such as valuations, tax declarations, or sale prices from around that period, speaks more directly to the question the article asks than current figures do. A shortfall that only shows up once you compare today's values, without a corresponding shortfall back at the time of partition, is not the kind of lesion Article 1098 is built to remedy.