These Seven fundamentals apply dynamically and simultaneously for calculating Islamic inheritance shares. You cannot leave one or more of these fundamentals to complete calculations per Sunni Islamic inheritance law.
FIRST - Eligibility & Reasons
The Eligibility of Islamic Inheritance distribution depends on many factors. For example, the certainty of death, heirs must be alive, Assets must be left by the deceased and free from all debts, expenses, and legal claims, and must have passed through Probate and/or settlement process. Reasons include a marital tie, blood relations, association of wala, kinsman, etc. And provided no impediments to inheritance.
SECOND - Prescribed sharer
There are twelve fixed or prescribed sharers that include Husband or Wife, Daughters (or Granddaughters), Father (or Grandfather), Mother (or Grandmothers), Full and Paternal Sisters, Maternal Brothers, and Maternal Sisters. The Shares for Granddaughters (i.e., Daughters of Sons how low soever), Grandfather (i.e., Father of Father), Grandmothers (i.e., Mother of Father, Mother of Mother how high soever) derived from Qiyas called analogical deductions. The Prescribed or fixed sharers fall into one of the fixed sharers 1/8, 1/6, 1/3, 1/2, 1/4, and 2/3. However, these shares cannot stay fixed in Radd and Awal scenarios. In the Radd situation, the total share is less than 1 (or 100%), so all shares are increased except Spouse shares to make the total share 1 (or 100%) provided Residuary does not survive. On the other hand, the Total share is more than 1 (or 100%) in the Awal situation, so all shares are reduced to make the total share 1.
THIRD - Residuary sharer
Calculate Residuary share = 1 - Fixed or Prescribed sharers. The residue is less than 1 (or 100%) in the case of Radd. The residue is more than 1 (or 100%) in the case of Awal. The residue is Zero in the case of Kamil, where the Residuary does not receive any share. Residuary are the Sons (or Sons of Sons how low soever), Daughters (or Daughters of Sons how low soever), Father (or Father of Father how high soever), Full and Paternal Siblings, and the Consanguine male relative of deceased.
FOURTH - Conditions
Every share has conditions attached to it. For example, the Daughter share is one-half (i.e., 1/2) if Single and two-thirds (i.e., 2/3) if Multiple with no Son(s) alive in both situations.
FIFTH - Blocking Rules
Every share has to go through full and partial blocking or exclusion (called "Hajb" in Arabic) rules except the Spouse share in some conditions as per Islamic law. For example, Father blocks Father of Father, Sons blocks Sons of Sons, and so on.
SIXTH - Apply to Assets
Calculate the final share after deducting funeral expenses, personal debts, taxes, zakat, kaffarat, and bequest. Muslim jurists have different opinions regarding paying the Zakat from the deceased person's property. According to the majority of fuqaha, it is obligatory to pay Zakat first, and then the residue will be distributed among the heirs. In comparison, the Hanafi school is of the opinion that it is not obligatory. Hanafi school opines that the Zakah will not be deducted because the deceased person is no more aptitude to execute any contract or fulfill a religious duty (Ref. Durr Al-Mukhtar and Hashiyat Ibn Abidin, Redd Al-Mukhtar, 6/760).
SEVENTH - Islamic estate planning
Islamic inheritance law forms the foundation of Islamic estate plans, Islamic Will, and Trusts.
Allah, the Most Glorified and the Most High, knows the best. As a human, We are limited to everything and can not perceive it in totality...