What are the fixed shares (Fara'id) for the surviving spouse?

Primary text

The fixed share for the husband is one-half when the deceased has no children or children of his son. The share is reduced to one-fourth if there are children or children of the son. The fixed share for the wife or wives is one-fourth when the deceased has no children or children of his son, and one-eighth if there are children or children of the son, regardless of whether there is one wife or four. This division is established by the consensus of the people of knowledge. The basis for this is found in the Quran: "And for you is half of what your wives leave if they have no child. But if they have a child, for you is a fourth of what they leave after any bequest they bequeath or a debt..." (Quran 4:12), and for the wives: "And for them is a fourth of what you leave if you have no child. But if you have a child, for them is an eighth of what you leave after any bequest you bequeath or a debt" (Quran 4:12). When there are multiple wives, they collectively receive the same share as one wife because giving each one the full fixed share would exceed the entire estate or exceed the husband's fixed share.