Short answer. The law looks first to the undisposed portion of the estate — property the will did not give to anyone. Only if that is not enough does Article 855 of the Civil Code allow the shortfall to be taken proportionally from the shares the will gave the other compulsory heirs.
What the law says
The share of a child or descendant omitted in a will must first be taken from the part of the estate not disposed of by the will, if any; if that is not sufficient, so much as may be necessary must be taken proportionally from the shares of the other compulsory heirs.
Civil Code, Article 855 — Share of an Omitted Child. Read the full provision →
The two-step rule under Article 855
Article 855 establishes a clear priority. Step one: look for property the will left undisposed — assets the testator owned but did not bequeath to anyone. Your omitted sibling's share is satisfied from that pool first. Step two: if the undisposed estate falls short, the remaining deficit is taken from the other compulsory heirs proportionally, meaning each heir gives up a part of their share in the same ratio as their shares bear to each other. No one heir is singled out to absorb the full shortfall.
What counts as the 'undisposed' portion
Property is undisposed when the testator owned it at death but the will made no specific gift or general bequest covering it. This can happen because the testator forgot to mention it, acquired it after writing the will, or deliberately left it outside the will's scope. All undisposed property is tapped before touching what the will already allocated to other heirs. This sequencing protects named beneficiaries as much as possible.
How the proportional reduction works
If the undisposed estate is zero or smaller than what the omitted sibling is owed, the remaining amount is spread across the other compulsory heirs in proportion to their individual shares. If one heir received twice as much as another under the will, they contribute twice as much to make up the shortfall. The reduction is not equal in absolute pesos — it is proportional so that the testator's relative allocation among the named heirs is preserved as closely as the law allows.
Why this matters in practice
Knowing the order matters for families dividing an estate with a mix of disposed and undisposed assets. It also matters for heirs who received specific items under the will — a parcel of land, a vehicle, a bank account. Those specific gifts are the last to be reduced, not the first. Before any family agreement is signed or court order requested, it is worth mapping out what was disposed, what was not, and whether the undisposed portion alone can cover the omitted sibling's share. That analysis can significantly affect who ultimately gives up what.