Short answer. Under Article 900 of the Civil Code, a sole surviving spouse's legitime is one-half of the hereditary estate, and the deceased may freely dispose of the other half. A narrower one-third legitime applies only where the marriage was solemnized in articulo mortis and the testator died within three months of it.
What the law says
If the only survivor is the widow or widower, she or he shall be entitled to one-half of the hereditary estate of the deceased spouse, and the testator may freely dispose of the other half.
Civil Code, Article 900 — Legitime Of Sole Surviving Spouse. Read the full provision →
The general rule: one-half of the estate
Article 900 states the ordinary rule plainly: if the only survivor is the widow or widower, she or he shall be entitled to one-half of the hereditary estate of the deceased spouse, and the testator may freely dispose of the other half. Where the spouse is the sole surviving compulsory heir — no children, no surviving parents — that spouse's legitime, the portion the law reserves for them, is fixed at half the estate. The other half is left to the deceased's free disposal, meaning it can be given away by will to anyone the testator chooses.
The narrower exception for a marriage in articulo mortis
The article carves out a specific, limited exception: if the marriage between the surviving spouse and the testator was solemnized in articulo mortis, and the testator died within three months from the time of the marriage, the legitime of the surviving spouse as the sole heir shall be one-third of the hereditary estate. A marriage in articulo mortis is one entered into at the point of death. Where that describes the marriage, and death followed within three months, the spouse's legitime drops from one-half to one-third.
When the exception itself does not apply
Article 900 immediately qualifies its own exception: it does not apply when they have been living as husband and wife for more than five years. In that situation the article says the legitime of the surviving spouse shall be that specified in the preceding paragraph — meaning the ordinary one-half rule is restored, even though the marriage itself was solemnized in articulo mortis and death came within three months. Long cohabitation before the marriage takes the situation back out of the reduced-share exception.
What to check to know which figure applies to you
Working out the correct legitime under this article means confirming three things: whether any children or surviving parents exist at all (this article assumes there are none), whether the marriage was solemnized in articulo mortis, and, if so, whether the couple had already been living together as husband and wife for more than five years before that marriage took place. Those facts determine whether the spouse's legitime is one-half or the narrower one-third.