Primary Sources & Scholarly Basis

• Quran: Key verses: An‑Nisa 4:11, 4:12, 4:176 (prescribed shares and sibling rules)
• Hadith literature: Sahih Muslim and Sahih Bukhari on inheritance practice and distribution.
• Classical jurists: Texts like Kitab al‑Farāʾiḍ and later commentaries (Hanafi/Shafi’i rulings differ slightly).
• Contemporary resources: academic articles and reputable Fiqh websites that compile case rulings for modern calculators (see references section).

Note: Some details vary by madhhab (school). A robust calculator should specify the methodology used (Hanafi, Shafi‘i, Maliki, Hanbali) or provide a configurable option.

Key Rules to Implement (Executive Summary)

Below are the core rules a reliable Faraid calculator must implement. This is a condensed technical checklist for developers and content authors.

1. Prescribed Shares (Fardh)

These fixed shares are explicitly set in the Quran and classical fiqh:

• Husband: ½ if no offspring; ¼ if offspring present.
• Wife(s): ¼ if no offspring; 1/8 if offspring present (divided among multiple wives).
• Daughter(s): ½ (single daughter, no son); 2/3 (two or more daughters, no son).
• Father: 1/6 when the deceased has offspring.
• Mother: 1/3 if no offspring & no multiple siblings; otherwise 1/6.
• Other relatives (grandparents, sisters, nephews) have 1/6, 1/12, 1/2, or 2/3 depending on combinations.

2. Ta’sib (Residual) and Male:Female Ratio

After fixed shares, eligible residual heirs (Aaseebs) divide the remainder. When males and females of the same class are present, the male receives double the female (2:1) in residual shares.

3. Blocking (Hajz) & Tasib Ranking

Certain heirs block others (e.g., son presence can block paternal uncles). A tasib ranking orders who receives residual shares; a reliable calculator must encode this hierarchy.

4. Awl (Proportional Reduction) & Radd (Redistribution)

If fixed shares sum to more than the estate, apply Awl: reduce proportionally so total = 1. If less than 1, apply Radd rules (except spouse) and distribute leftover among eligible heirs.

5. Special Cases & Juristic Rulings

Implement special logics: Umar’s ruling, sister vs grandfather adjustments, role promotion (granddaughter → daughter), and refusal of spouse share increase. These edge cases are the reason calculators must annotate decisions for users.

How a Calculator Implements the Rules (Technical Flow)

1. Input validation: Estate value (net of debts), counts of each heir, and toggles for special notes.
2. Determine eligible heirs: Apply blocking rules to exclude heirs immediately blocked.
3. Calculate prescribed shares: Compute fractions for each fixed heir.
4. Sum shares: Compare to 1 (whole estate).
5. Apply Awl or Radd if needed, or compute residual allocation via Ta’sib rules.
6. Finalize amounts: Convert fractions to percentages and currency values; present results with explanations and references.

Worked Examples (Illustrative)

These examples show typical scenarios and how a calculator would produce results. All examples assume the estate = 1,200,000 (currency units) net of debts.

Example 1 — Simple: Deceased leaves wife and one son

Input: Wife = 1, Son = 1
Logic: Wife gets 1/8 (spouse share when children exist). Son is residual heir and receives remainder (7/8).
Output: Wife = 1/8 → 150,000; Son = 7/8 → 1,050,000.

Example 2 — Daughter only (single daughter, no son)

Input: Daughter = 1
Logic: Single daughter with no sons gets 1/2 (prescribed). Residual: none.
Output: Daughter = 1/2 → 600,000; Remaining 600,000 distributed per Radd rules if eligible (none) → treatment depends on other relatives.

Example 3 — Complex: Wife, mother, father, two daughters

Input: Wife=1, Mother=1, Father=1, Daughters=2; Estate=1,200,000
Logic: Wife (1/8 — since offspring exist) = 150,000; Mother (1/6 if offspring) = 200,000; Father (1/6 with offspring) = 200,000; Daughters (2 or more without son → 2/3) = 800,000. Sum of shares = 1/8 + 1/6 + 1/6 + 2/3 = compute fractions and detect Awl if >1 → here 1/8 + 1/6 + 1/6 + 2/3 = 1 (calculator confirms consistency). Final amounts: Wife 150k, Mother 200k, Father 200k, Daughters share 800k (shared equally = 400k each).

Note: These illustrative numbers are simplified. A production calculator should show exact fractions and explain any Awl/Radd adjustments used.

Benefits, Limitations & Best Practices

Benefits: Accuracy, clarity, time savings, auditability, and educational value. Calculators reduce disputes by providing clear, documented allocations with references.

Limitations: Differences between schools of law; local statutory rules may vary; exceptional cases might need scholarly fatwa; legal enforceability varies by jurisdiction.

Best practices: Always enter net estate (after debts and funeral expenses), save or print results, and consult a qualified scholar for contested or high‑value estates.